# YBA-1A Bass Master Mark II - Many Pics - Service Recommendations?



## keto

*EDITED *Here are the questions I still have, I will change this list as I learn more. I am working from this schematic http://www.0rigami.com/vb/traynor_bassmaster_mkii_yba1a.pdf - the only variance I physically see *so far* is the diodes, see question #2 below.

1. Changing out the power cord - I intend to bypass the courtesy plug and the ground switch - can I wire the fan directly to the on/off AC switch?
2. What product could be used to hose down the interior, is there such a thing made for cleaning electronics?
3. The schematic shows PH204 diodes, but I don't see any in the amp. I physically see 5 @ 1N5061 - I don't know how to test them, are they something that should be replaced? If so, with what modern spec part?
4. Schematic shows varistors 6RS20XXXX - I don't even know what they look like, though I know they come off the OT and are said to be subject to failure - where am I looking?
5. Some talk of changing NFB. My tech knowledge in this area is essentially zero - what am I looking to gain, which part(s) are involved.

*WHAT I DO KNOW
*1. Change all (6) electrolytic caps. This doesn't count the cap cans, which look to be a huge pain to get out. Was advised below to try it with them in and see if any hum.
2. Job 1 is change out to a proper 3 pronged plug. I'm actually going to bypass the ground switch and courtesy outlet (going through the AC switch and fuse, adding a chassis ground for the cord), though the parts will be left in the amp. (see #1 above)
3. Going to change R25 (which may have been changed already) to [email protected] 1K 10W, one going to each power tube socket (instead of 1K @ 10W servicing both sockets), and remove the bridge between sockets
4. Check power tube sockets for arcing. Retension/clean all sockets. Clean all jacks.



So, this belongs to the bass player in the band. He says it was given to him, don't know when or by whom. 



Would I be correct in assuming this is a '69 or '70?


I know the fan (or, at least, *a* fan) is original. Haven't checked function yet, I know it runs wall voltage. I took it out, it spins fairly freely by hand. Cleaned it up, but not internally.


I can't begin to tell you how much iron is in this thing. I bet just the chassis is close to 40 lbs.


Tube chart's mostly gone.


He was told it has fresh tubes. LOL. I have no way of testing them other than throwing them into one of my other amps.


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## keto

Anyways, he says it's blowing fuses - I don't think he's ever heard it working. So, I asked him to drag it along to band practice and said I'd take a look and see. There's a great link with schematics, owner's manuals, and some details here http://www.0rigami.com/vb/models.html#bassmastermkiiyba-1a , so I printed off some of the schems. When I opened it up, well, it's a filthy mess in there...and my untrained eye says it's probably never been serviced. *EDITED the one possible exception is the big cement resistor, schem says 470R 10W, in the amp it's 1K 10W, which I read is common to change. I intend to further change it, see first post above.*




I know the 80 MFD caps need to be changed out. The cap cans I was advised below to not change them at first, if amp still hums then change them but it will be a huge pain.


Going to change this to a proper 3 pronged plug setup, going to bypass the courtesy outlet and the ground switch/death cap.


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## dcole

Hey Keto,

That thing has definitely not been touch by a service tech. I can answer a few questions for you but not all:

1) The fan is shown on the schematic and should be a 120Vac model thus do not try a 12Vdc fan there.
2) The power cord should be replaced with a modern 3 conductor cord and the chassis grounded accordingly.

If you are unable to do it yourself, I would take this amp to a tech to troubleshoot. He should be able to check the tubes and replace all the electrolytics as well as update the power cord. It will cost some money but in the end your bass player would come out a head if he decided to sell it.

Thanks,

David


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## J-75

Ditto re: add a proper grounded power cord. You may want to do a search on "death cap" and compare with your circuit and take necessary action.
Replace the three 8 Mfd. electrolytics. The 40/40 Mallory cans can be tried out as-is, since they seem to last a long time, so if you get a lot of hum, then replace them (tedious job).
That charred blue wire laying across one of the rectifiers is suspicious (how hot does/did that rectifier get?), or is it just accidental from a slip of a soldering iron during assembly?
I highly recommend using a tech who knows tube amps to do the work.


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## keto

Ah, so those little guys are rectifiers, I was going to ask if they were diodes. To me it looks like an iron touch on the wire - it's on the top side moreso than underneath where the parts are. *EDITED the wire above the diodes, with the burn mark, the burn mark is 100% on the top side of the wire, it is clean green and pristine on the underside close to the diodes (ok it's blue, blue didn't rhyme.). It also sits quite far above them, the pic is deceptive, there's a good 1/2"-3/4" gap there.* After I posted the original topic I looked closer and realized those cap cans are totally soldered in - and a lot of the soldering on the guts looks more like welding lol. They had a HOT iron when they built this thing.

Yeah, he's a young father of 3 without a lot of spare change, that's one of the reasons I'm looking at it, rather than a pro tech, and asking advice here. I know enough to discharge caps, have good soldering skills and can change out parts. The grounded cord would be easy enough, I was sure I was right but wanted a 2nd opinion (thanks). Where I fall short is in experience and knowing where to look first to diagnose the blowing fuses.


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## loudtubeamps

J-75 said:


> Ditto re: add a proper grounded power cord. You may want to do a search on "death cap" and compare with your circuit and take necessary action.
> Replace the three 80 Mfd. electrolytics. The 40/40 Mallory cans can be tried out as-is, since they seem to last a long time, so if you get a lot of hum, then replace them (tedious job).
> That charred blue wire laying across one of the rectifiers is suspicious (how hot does/did that rectifier get?), or is it just accidental from a slip of a soldering iron during assembly?
> I highly recommend using a tech who knows tube amps to do the work.


Agreed..or, if u are comfortable doing the work, I would start by cleaning the _whole_ thing up, freshen up _all_ of the electrolytics (all are available in the same packages as the original caps) and tubes as well as the required maintenence for a _stock_ amp such as this.
Re-tension tube socket clips, inspect for any signs of carbon arching on tube socket bases,inspect all solder points and wiring.
After the basics have been addressed, the fuse problem will probably go away, if not at least U will have eliminated the obvious weak points.


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## keto

loudtubeamps said:


> ........................... *(all are available in the same packages as the original caps)* ...................


Even the big cardboard/paper ones? Where?

Re: cleaning - is there a product used for hosing down (lol) old electronics?? The thought of going in there with a wet rag is not appealing. I already ran the air duster in there (after the pics) but it doesn't give a great result.


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## keto

So I hadn't looked at the schematic prior to posting the above, now I've had a go through it.

The 2 electrolytic 8MFD caps,* those are bias supply, correct?* (I know they get changed regardless). They look leaky/slightly popped on the ends.

The schematic shows [email protected] diodes listed in the box at the bottom, but only 1 in the circuit - there are none I can see on the amp. The box listing shows [email protected] If my analysis is correct, they have used 4 @ 1N5061 *in place of* 6 @ PH204 (coming off the PT), and 1 @ 1N5061 *in place of* the PH204 leading to the bias supply portion of the circuit. Does this sound correct, and are those diodes candidates to be replaced, or should they be fine?

I get the fan part of the circuit now. I took the fan out of the headshell - nice heavy construction, though no idea whether it works or how gunked up it might be inside. Recommend to replace, or try it and see?

I also understand about cleaning and retensioning the tube sockets, as well as cleaning all the input/output jacks.


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## loudtubeamps

keto said:


> Even the big cardboard/paper ones? Where?
> 
> Re: cleaning - is there a product used for hosing down (lol) old electronics?? MG Chemicals - 409B-340G - Chemicals - Cleaners & Degreasers - Allied Electronics
> The thought of going in there with a wet rag is not appealing. I already ran the air duster in there (after the pics) but it doesn't give a great result.


 Hi keto. The caps won't be in cardboard anymore but those axial lead types are readily available. U may have compromise slightly and go up or down in values a bit.There are people selling NOS caps that would be similar, if the not the same in value and construction. I _would not_ use any of the NOS _electrolytics_. Here a some links to get U started.
High Voltage Electrolytic and Film Capacitors for Tube Radios

Capacitors | Antique Electronic Supply

Aluminum Electrolytic Products
I'm sure some of the other forum members who are doing repairs on a daily basis may point u to the exact caps required.


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## keto

OK I know what axial electrolytics are, and their ratings. It was more the packaging I was curious about, but modern packaging/production seems the way to go. The guy at justradios actually lists 80MFD, though I figure 100UF would be a suitable replacement if needs be.

People talk online about changing the negative feedback. That's some theory I don't know and don't know which parts on the schem supply it. Any thoughts?


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## nonreverb

Apart from what others mention here which are necessities such as cap. replacement, I see some blackening around one of the power tube sockets. Perhaps an arc. The YBA-1A is higher voltage than it's earlier cousin the YBA-1 and I've had to replace bad sockets on them before. Since it's blowing fuses, I'll bet you have a toasty power tube.


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## keto

Thank you nonreverb (and others above).

I have consolidated a list of questions a) still remaining and b) asked and answered, in the first post at the top. I also edited some comments in the 2nd post to reflect what I now know.


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## loudtubeamps

2. What product could be used to hose down the interior, is there such a thing made for cleaning electronics?

MG Chemicals - 409B-340G - Chemicals - Cleaners & Degreasers - Allied Electronics
Just don't hose down the rivet board too much.A bit of spray and a toothbrush to lift the gunk and a bit more spray to rinse.
"Keeps the doctor away."

1. Changing out the power cord - I intend to bypass the courtesy plug and the ground switch - can I wire the fan directly to the on/off AC switch?

If it's a _120vac_ and _not a 12vdc_, should be good to go. I know this sounds silly , but I've seen it done before!! POW!

3. The schematic shows PH204 diodes, but I don't see any in the amp. I physically see 5 @ 1N5061 - I don't know how to test them, are they something that should be replaced? If so, with what modern spec part?

Those 5 diodes that constitute your rectifier(s) _should_ be just fine. They very rarely go south.
See this link. Re: your rectifier layout.740104_YBA1.gif 2065×3105 pixels

4. Schematic shows varistors 6RS20XXXX - I don't even know what they look like, though I know they come off the OT and are said to be subject to failure - where am I looking?

They are, I believe, a set of diodes that were used in some amp designs (as a safety feature) to protect the circuits and O/P transformer if the O.P. tubes decided to have some kind of melt down. I haven't seen many old Traynor amps with these, if any?? Can't recall!!

Reading on...........The dual electrolytic cans are no problem if U have, let's say, a Weller soldering gun









or a big old, ugly iron









and a good tight, clean, well tinned tip. I would cut the leads off at the can terminal lugs, cut the can ground lugs off with a good pair of side cutters, remove the old cap can and then go in with your Weller and remove the remaining lugs ends and old solder.This method works best for the simple reason that with the cap(s) can gone, U have just removed a big heat sink which would be sucking up all of your heat that needs to be conducted into the chassis.


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## Lincoln

loudtubeamps said:


> or a big old, ugly iron


A brake drum & rotor lathe? 



Sorry for the thread hi-jack/detour Keto


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## keto

Can you read C19 and R31 in that schem? It appears to vary a lot from the earlier one I'm using. http://www.lynx.bc.ca/~jc/740104_YBA1.gif


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## parkhead

c19 looks like 10uf at 160 volts 
r31 cannot be read in the scan go with matching whats in your amp 
since that is the bias supply and might be subject to change 



clean it out with some brushes and your shop vac 
replace all electrolytics including the bias caps 
if you can't match the MFD rating on the caps its ok ... use a few less MFD especially towards the pre amp 
you will probably need new output tubes 


once all this is done and the amp is quiet and stable you can tune the pre amp for guitar 

here are some suggestions 

minimalist: 
take the .001 cap attached to the bright volume control lift one leg ... solder a 270 to 470k resistor between the lifted leg and the pot 
so you .001 is now in series with the resistor ... this should take some edge of the brightness

2nd degree minimalist 
option 2 is to lift that capacitor completely and if the legs are long enough solder it over one of the 100k channel mix resistors 
this will produce a bright lift fairly close to the marshall frequency 500pf over 270k .... 1000pf over 100k 
don't use a cap on the volume control 

using a bright cap on a volume makes the brightness jump around when you hit the amp with a drive pedal .... not cool 


Part 2 
a little more invasive but worth it if dialing in a traditional ac/dc big Malcom Young kerrang 
...you need one or two new .01 caps at 400 volt 

remove the bright channel .02 v1 coupling cap replace it with a new .01 
remove the big .1 @ 400volt bass mustard cap put your .02 mustard just removed in its place, as the bass cap 
remove the .1 200volt back of the phase inverter cap and replace it with the larger .1 removed from the bass tone stack
remove the phase inverter input cap .02 and replace it with .01 

the amp will sound almost identical but the bottom end will sound muscular and tight instead of wobbly and loose 
harmonics will be more balanced 

part 2 
if any of the original coupling caps are already replaced or have failed feel free to use higher values in certain spots 
.02's sound great replacing .1's in the power section 

there is a Marshall mod guy in my area who moves the .002 v1 coupling cap to the Phase inverter and the .02 from the inverter
back to the v1 on lead type amps ... very subtle but a very cool idea his amps look stock but sing nicely 

the key way to look at the process is that you want to reduce some non musical frequencies and that should open up some gain and resonance for some of the more ringing guitar harmonics... you do want to be subtle since you could simply reduce all sorts of coupling caps to .002 or .001 end up with a modern sounding nasal amp 

There was a great thread on one of the Marshall build forums a while back where the guy could not get .02 mullard Mustard caps to build his jtm45 amp. He got his hands on a bunch of .018's and used them wherever the circuit called for .02 caps. He then made a bunch of clips of the amp and it sounded pretty great ... 
He then got his coveted .02 caps and redid those in the amp and the new clips were no where near as magical... I think he was frustrated ... 

which leads to Parkhead's number one rule of secret vintage cap MOJO 
maybe people want brand X vintage .02 caps because they sound more like modern .01 caps not because they have some build secret ...

also keep in mind it's said you have to move a part value by a factor of 10X to hear any audible change 
so .02 try to .002 even if you select .01, because .002 will clearly tell you where you are heading ... 

exiting V1 .02 is passing as low as 79.2 hz, .002 is passing above 792. hz 
and .01 is passing 159hz 
this does not mean you do not hear anything below 79 or 159hz ... but that is where the 6db rolloff starts 

incidentally 792hz and up is the frequency Marshall designers LOVE to goose 

if you look at the inverter input cap .02 & 1meg give a high pass of 8hz 
so swapping in a .002 should be inaudible at 79hz and may tune out some unwanted rumble 

very subtle stuff but I think its more effective to listen to an amp and look at tuning issues using this technique rather than assume 
great old amps sounded a certain way because the capacitors were made by Magic elves using unobtainium 

don't forget when the fender, Marshall and vox folks chose their cap values they settled it by ear when they heard what they wanted 
using the potentially crappy low cost supplier parts they would use in production and had on hand & that's why first run vintage stuff usually sounds the best 


P


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## nonreverb

Great explanation Parkhead.


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## J-75

Can anyone explain why restored old guitar amps *must* have Mullard _mustard_ caps, while restored old Hammonds *must* have Sprague _orange drops_?
Is brand/colour that important? :sSig_Idontgetit:

Caps come with a value, tolerance, temp. coefficient, breakdown voltage. The first two parameters are what really matter in tone circuits. Would it make any difference if you measured 18 inches with an aluminium yardstick versus a plastic one? When I was a kid, we all had to have a certain brand of running shoe - no other would do. Now that I've aged considerably, nothing has changed.


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## keto

J-75 said:


> ..........*Would it make any difference if you measured 18 inches with an aluminium yardstick versus a plastic one?* ........


Depends on the ambient temperature, sure!

I have no dog in the caps debate. Thanks for the explo, parkhead, but this is strictly low budget 'get it up and running doing as little as possible', at least for now. Owner has a link to this thread, so I'll make sure he see's the info.


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## parkhead

J-75 said:


> Can anyone explain why restored old guitar amps *must* have Mullard _mustard_ caps, while restored old Hammonds *must* have Sprague _orange drops_?
> Is brand/colour that important? :sSig_Idontgetit:
> 
> Caps come with a value, tolerance, temp. coefficient, breakdown voltage. The first two parameters are what really matter in tone circuits. Would it make any difference if you measured 18 inches with an aluminium yardstick versus a plastic one? When I was a kid, we all had to have a certain brand of running shoe - no other would do. Now that I've aged considerably, nothing has changed.


Easy... if you use the wrong parts on a restoration its not a restoration...

there was a guy a while ago selling a tremolux and he asked me why is everyone walking away after they look at it 
& all the astron caps had been replaced with orange drops every one !

IMHO (and the buyers opinions) that amp was ruined, since who ever did the work obviously changed some parts that were still good 
since ALL the signal caps were new... 
since the person who did the work was too stupid to be respectful and selective in his work there is no doubt in my mind other issues would become apparent with his work over time 

I personally CAN hear the difference between orange drops, and mallory 150s ... one or two won't ruin an amp 
but when possible I use the correct make of vintage signal cap on a vintage amp 

on the other hand people trying to build a Marshall clone are trying to get the right parts because they do not know 
which parts were actually part of the magic... in fairness they are taking the right approach if they are trying to establish 
a baseline and build their tone from there 

conversely 
Many people do not understand the critical importance of REAL PAF's in reproducing allman, early clapton, kossoff and other burst tones...
they are mislead by the fact that visually the gibson pickup is almost unchanged over the years and Gibson does a lot of marketing of their current 
reproduction offerings 


Strats are the opposite scenario I have pre cbs strats and I like any strat with the right repro pickups ... they all sound like strats 
different strats but strats ... the right trem blocks are needed but we should all know that now thanks to callaham & Eric Johnson 

Tele's forget about it ... if you've played a real black Guard 50 -53 tele your life is ruined... I have tried and never duplicated the ones I have played 
it took me 15 years to find the right pickups and bits to replace my retired 63 tele and the new guitar is very different but at least its cool 


P


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## nonreverb

Parkhead, here's some thoughts on some of your statements:

*"IMHO (and the buyers opinions) that amp was ruined, since who ever did the work obviously changed some parts that were still good 
since ALL the signal caps were new... 
since the person who did the work was too stupid to be respectful and selective in his work there is no doubt in my mind other issues would become apparent with his work over time "
*
Let's take a different perspective for a moment and suppose the "stupid" person was told to change the parts in the customer's amp. The amp belongs to the customer and they are insistent. 
Whatever they wish to do with it is their business regardless of your beliefs. If you're a tech, you have every right to bring to their attention your concerns BUT that's your job and if they are happy with the result so be it. That's what matters. Besides, you can make make sure they keep the parts so it's possible to revert it back.
Don't get me wrong, I don't change stuff that doesn't need changing and most self respecting techs won't but there are customers out there that are just as much at fault as there are techs.

*I personally CAN hear the difference between orange drops, and mallory 150s ... one or two won't ruin an amp 
but when possible I use the correct make of vintage signal cap on a vintage amp 

*I thinks resistor drift creates far more audio variation than any perceived cap difference. Unless of course they're wax caps as they are usually extremely far off spec. Blind audio test is the only fair way to test one's claimed cap sonic sensitivity.

*Many people do not understand the critical importance of REAL PAF's in reproducing allman, early clapton, kossoff and other burst tones...
they are mislead by the fact that visually the gibson pickup is almost unchanged over the years and Gibson does a lot of marketing of their current 
reproduction offerings

*You're dredging up this discussion again? I thought it was beaten to death the last time....


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## parkhead

sometimes the stupid person is the customer who read ... ON THE INTERNET that orange drops are better 

I can hear the difference in caps ... it's probably a curse 

The PAF thing is worth repeating 

Bottom line just because its written on the internet does not mean its true 

now I must go feed my uncle and mentor to 120 ravenous dogs... as punishment for plotting against me 

p


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## nonreverb

Indeed, the same rational can be applied to the whole PAF mythology. There are 4000 reasons that people believe they're better and each is worth a $.
PAF's and early patent numbers were made for round 8 years. Not all of them are good and the fact that they underwent significant changes during production further underscores the fact that much of the mythology is just that. Compound that with the undeniable fact that the magnets under ideal conditions have naturally demagnetized by at least 5% since new or worse, have been degaussed by general use/abuse,and you wind up with a pickup that does not sound the same as it was when new. 
Sure, there are some sets that have weathered well since new and sound great. I'm sure there's a few sets of Thobak MXV's that sound spectacular too.....at a mere fraction of the price.




parkhead said:


> sometimes the stupid person is the customer who read ... ON THE INTERNET that orange drops are better
> 
> I can hear the difference in caps ... it's probably a curse
> 
> The PAF thing is worth repeating
> 
> Bottom line just because its written on the internet does not mean its true
> 
> now I must go feed my uncle and mentor to 120 ravenous dogs... as punishment for plotting against me
> 
> p


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## LydianGuitars

nonreverb said:


> Compound that with the undeniable fact that the magnets under ideal conditions have naturally demagnetized by at least 5% since new or worse, have been degaussed by general use/abuse,and you wind up with a pickup that does not sound the same as it was when new.


I see this statement every so often on the 'net about magnets demagnetizing. 

Magnets will demagnetize when heated (over the curie temp), which is not possible on a guitar.
You can also demagnetize with a strong magnetic field - also highly unlikely on a guitar.
The last method of demagnetizing is via shock. Unless you bring a hammer to the pickups, I'm not sure how this can happen.

Given the above, its pretty much impossible that a magnet loses "at least 5% since new or worse", unless I'm missing something? Maybe this is a phenomenon reserved to humbucking pickups only where each bobbin has opposing magnets? Over time, I could see how the constant opposing fields could weaken the filed of each magnet. I'd be surprised that the loss would be significant though. I'm actually curious about this because it would affect some types of speakers more than others.


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## nonreverb

alnico magnets do not hold their magnetism forever. Over the course of decades, it slowly demagnetizes. alnico also has the particular distinction of being easily affected by strong magnetic fields or being stuck. Ever wonder why some old Strats sound "glassy"? They didn't necessarily start out that way. The alnico slugs are slowly weakening. 
Since the last PAF was made over 50 years ago now, rest assured, the magnetic filed in most of those magnets is not what it once was.



LydianGuitars said:


> I see this statement every so often on the 'net about magnets demagnetizing.
> 
> Magnets will demagnetize when heated (over the curie temp), which is not possible on a guitar.
> You can also demagnetize with a strong magnetic field - also highly unlikely on a guitar.
> The last method of demagnetizing is via shock. Unless you bring a hammer to the pickups, I'm not sure how this can happen.
> 
> Given the above, its pretty much impossible that a magnet loses "at least 5% since new or worse", unless I'm missing something? Maybe this is a phenomenon reserved to humbucking pickups only where each bobbin has opposing magnets? Over time, I could see how the constant opposing fields could weaken the filed of each magnet. I'd be surprised that the loss would be significant though. I'm actually curious about this because it would affect some types of speakers more than others.


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## keto

Let's keep this to old Traynors, and the servicing thereof....mmkay?


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## nonreverb

Indeed, I've played a part in hijacking this thread. My apologies.




keto said:


> Let's keep this to old Traynors, and the servicing thereof....mmkay?


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## jb welder

keto said:


> Let's keep this to old Traynors, and the servicing thereof....mmkay?


Good to see this back on track!

OK everyone. Now that he's changed all the caps, cleaned out the chassis, added a 3 prong, replaced a socket, modded the heck out of it, what if it turns out it was blowing fuses because the PT or OT is gone? :frown-new:
Four F rule : fix f'n fault first!
It was apparent right off the top that the owner didn't have much of a budget for this. I'm guessing first order of business would be to verify the iron.

P.S. There seem to be a few things not matching the schematic, there are quite a few versions, is this the closest one?


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## jb welder

Sorry if that sounded a little harsh, but in a shop situation for this particular scenario, if I did anything before finding out why the fuse is blowing I would probably be putting my job on the line. :smile-new:

Keto: do you have a light-bulb limiter, or a bunch of 5amp slow-blow fuses? Bulb limiter is easy to make and is very handy. I'll bet once you fix this amp, it won't be your last, so might as well build one.
First off, try the amp with the power tubes removed. With power on but in standby mode, does fuse blow? (or light bulb limiter glow bright) If not flip standby switch. Fuse still ok or blown?


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## keto

No, that's OK jb..I know you're right, but the path of least resistance (whoo bad pun) = where I have the most knowledge, and swapping out caps and cord is what I can do in my spare time at little expense with the knowledge and tools I have....I don't know anything about testing transformers. I see you're giving me a head start, but new caps should land tomorrow and I've already removed some of the old ones, so too late to go down that path first now 

I did stock up on a few fuses, so after caps change (and a couple resistors) if it pops a fuse I'll be back in here as fast as lightning.


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## jb welder

I wasn't singling you out Keto, rather those of us who should know better. And I wasn't trying to imply I haven't done the same myself, I have found out the hard way!
No longer working for someone else, like others here, it's easy to get carried away rather than dealing with the fault first. Sometimes you get beat, spend too much parts and labour only to find out there are other problems leading to the repair being declined.
But even worse, especially for a novice, is the possibility of creating other problems before getting to the original fault. It happens a lot. Someone inexperienced tackles other jobs, or does mods, or blind parts swaps, then repairs the original fault, but now finds there are other problems. Often those "other problems" turn out to have been created by the other "non-critical" work.
For these reasons among others, fixing the fault before other work is the cardinal rule.
The other "red flag" in this particular case is that it seems the owner has never had it in running condition. So it really could be anything causing the fuse to blow.
So try to do as little as possible before dealing with the fuse issue, and triple check your work!
Good luck, I'm sure you'll have plenty of help available here, and a captive audience waiting to hear the outcome.

P.S. You can try the tests I suggested before you install the new caps. Post your results.


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## parkhead

I dont agree with this 100% 

pull the tubes replace the fuse fire it up if the fuse blows you have a diode or cap problem 

if the fuse does not blow you have bad power tubes...

just looking at those MIJ el34s I suspect one has a short ...

the odds of a bad power transformer are aout 2% OR LESS and there should be physical evidence like no pilot light burns or an acrid burnt 

smell

one should never tweak a broken amp, but considering the amp is 40 years old and neglected the simplest course of action is to 

referesh all theitems past their best before date and then move on ....

if there was evidence (none described) of a transformer problem it would be a different story 

....I have also found that its a waste of time to trace faults on an amp that is full of expired capacitors 99% of the time the issues are caused 

by the worn out junk 

p


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## nonreverb

In my experience, an amp with one fuse only, it's usually a bad power tube, rectifier tube or diode in the power supply. Much depends on how fast/what happens when the unit is turned on. If it blows instantly, diode. completely shorted power tube or shorted cap and yes, on occasion transformer. If it takes it's time, rectifier tube, heater shorted power tube or some intermittent on the board. Years of doing this gig gives you the experience to look at right places for specific problems.
Of course with a mains fuse and HT fuse, diagnosis is much simpler.
To give you an idea, I probably replace around a dozen transformers a year due to failure. Marshalls being the most common.


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## WCGill

Like Parkhead says, yank the tubes and see what happens. Measure the filter caps with your VOM meter-any wonky readings compared to normal or new indicates problems here. Transformer problems tend to be rarer in these parts.


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## loudtubeamps

The only instance I can recall of a Hammond xformer (O/P in my case) failing was due to user error.The customer was using a shielded patch cable to connect the amp to the cab and pushing the amp pretty hard, happened twice!! After the first replacement, I asked him to bring in everything he was using when the second tranni failed. That was over 20 years ago and as far as I know the amp has been fine.
Jb's comment Re: bulb limiter is a good thing to have. Cheap to make and saves fuses and frustration.Measurements from the schematic cannot be made accurately because of the significant voltage drop, but for troubleshooting a live amp that would be otherwise continue blowing fuses , they are great. Also good (apparently)when replacing and initially powering up fresh electrolytic power supply caps.
If on _that tight budget_, re: to the original tubes, a goood chance the pre- amp tubes can be re-used, may even be better than new replacements. With respect to the El's, as mentioned, look for carbon arching on the tube base and tube socket and scrape off any if found. They may be salvaged as well. I have some oldies from that far back that are still stable. The test parkhead suggests is going to direct your troubleshooting to the right area of concern. As suggested........Once the amp is up and running,then u can play with modding.
Cheers, d


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## loudtubeamps

found this .............Dump find! Yba-1 re load tester.
cheers, d


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## nonreverb

Indeed, the bulb limiter is a must have when servicing solid state amps in particular.



loudtubeamps said:


> The only instance I can recall of a Hammond xformer (O/P in my case) failing was due to user error.The customer was using a shielded patch cable and pusing the amp pretty hard, happened twice!! After the first replacement, I asked him to bring in everything he was using when the second tranni failed. That was over 20 years ago and as far as I know the amp has been fine.
> Jb's comment Re: bulb limiter is a good thing to have. Cheap to make and saves fuses and frustration.Measurements from the schematic cannot be made accurately because of the significant voltage drop, but for troubleshooting a live amp that would be otherwise continue blowing fuses , they are great. Also good when replacing and initially powering up fresh electrolytic power supply caps.


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## jb welder

parkhead said:


> I dont agree with this 100%
> 
> pull the tubes replace the fuse fire it up if the fuse blows you have a diode or cap problem


Except if it's a bad transformer or bad wiring or an arced socket or a few other things. I agree with you that it will almost always be a diode or cap. But there's still the small chance it's something major.
The owner has never had it running.

Imagine someone was thinking of buying it but brought it to you to see if he should buy it. It's blowing fuses and he doesn't have much money to fix it if it's a major repair.
You're not going to check out the transformers? 

Like the others have commented, shorted transformers are rare, especially these big Hammonds. In hundreds of Traynor's, I don't know if I've seen any bad ones. But I've sure seen tin-foiled fuses, 25A automotive fuses, etc.
Starting out by eliminating the most costly components as suspects is just good practice. I'm not going to argue any more, we'll just have to agree to disagree. I'm fairly sure the actual fault will prove I was overly cautious, _this time_. I sure hope so.

Edit: To be clear, I'm not insisting on some specific or extensive transformer testing. Just eliminating them as a cause of fuse-blowing before doing other work.


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## parkhead

Keep in mind this is the internet so this is INFO -TAINMENT 

I am assuming you will get the amp up and running if you service all of the components that are overdue 

Though many assume I am some sort of tech I am not and I always defer to wisdom of those who have more shocks that I 

While I am not a tech I an not a noob to this toob amp thing ... unfortunatly having many years of experience in these matters 

(panicked people) 

99% of the time time the owner makes two assumptions

A: its just dusty have a look see, it can't be more than your minimum bench fee... in fact I really believe this will be one of those 

feel good experiences where you turn to me and say Justa a loose bolt no charge ... RIGGGHT???? 


B: oh my GOD I have blown a transformer ... its gotta be a transformer ...or some other expensive part ... this is the END OF 

THE WORLD ....

in scenario B it's always a Bad Patch cable, Dead Battery, loose input Jack, pot turning and grounding out ...loose euro plug AC 

cable is #1... batterys #2... Patch #3 

in scenario A its always ... really DUST how 'bout some basic service since you have had this 20 years 

this Leads to Parkheads #1 rule of Diagnosis 

Start with the cheapest components first ... 

anyway all this talk about the proper way to do things is not fun lets talk about making that sucker scream ....

get her working and have some FUN 

p


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## nonreverb

There keto....see how easy that was?


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## keto

Meh, I'm not scared of changing out a few caps and resistors and rewiring the power cord (though I am going to draw it all out and have you guys vet it before I wire it up and plug it in). I ordered parts from justradios but still don't have them, and have removed the old caps so I'm sitting in stasis on this for now.


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## loudtubeamps

While you're waiting for parts, spend 10 bucks and build yourself that load tester, assuming u don't have one already? Money well spent!
Cheers, d


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## keto

OK so I drew out the stock power cord connections:


And then what I imagine the 3 prong cord mod should look like, bypassing the courtesy outlet and the ground switch. But I'm a bit thrown by the fact that the AC switch is just 2 poles unlike the 2 amps I've built. Is it correct, that I hook the transformer directly both wires to the switch? Also, in the original, the standby switch comes from a wire from the transformer (and what I imagine is the corresponding/partner wire from the xformer goes to ground). Is this left 'as is'? Also, I forgot to add in the fan connections, which I imagine I could run to the 2 fuse connections or to the 2 AC switch connections...yes?


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## nonreverb

Looks like you have the hot and neutral tied together via the switch and fuse.......bad idea.
One of the AC mains wires should go directly to the transformer (usually neutral) the other follows through the fuse and then on to the switch and then to the other wire of the transformer. The third green wire is correct.


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## keto

Yeah, I suspected something wrong. I'm not wrapping my head around this though. Black power cord to the switch, as I have it. White is neutral of the cord, it goes to the end of the fuse, neutral transformer to the side of the fuse, one side of the fan can go there too (I know I should probably have to observe polarity on the fan or it will spin backwards). Power side of the transformer to the switch, also the other end of the fan. 

Like so??


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## dtsaudio

The white wire of the power cord goes directly to the transformer and the fan, NOT through the fuse. The black wire of the power cord goes to the fuse first; then goes to the switch. The other side of the switch then goes to the transformer and fan. 
There is no polarity to the fan. It will only rotate in one direction.


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## keto

so the black wire goes to both sides of the fuse, with a gap obviously?


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## WCGill

Hot wire in (black) to the *end* of the fuse, out from the side connection to the switch. Switch to TX and fan, white directly to TX and fan, much as you have it.


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## loudtubeamps

Some googlee wooglee........
here are 2 examples I pulled up in about 15 seconds off of the WWW.
Cheers, D
see link ....How To Ground An Old Guitar Amp? - Gearslutz.com










I prefer switch first and then fuse. like this one....FWIW
Safest hook up to fuse holder would be _incoming hot feed to fuse holder *tip* lug_, and your _fused feed_ transformer connection ,connects to _fuse holder_ _lug nearest fuse holder cap._
Fan would/could go to SA2 and neutral/white AC lead.




 link here to info as well.....Amp Shocks


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## loudtubeamps

WCGill said:


> Hot wire in (black) to the *end* of the fuse, out from the side connection to the switch. Switch to TX and fan, white directly to TX and fan, much as you have it.


 *Right on! *I posted my 2 cents and then saw yours.My bad. Cheers, d


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## keto

Whew, thanks men!


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## WCGill

loudtubeamps said:


> *Right on! *I posted my 2 cents and then saw yours.My bad. Cheers, d


Picture's worth a thousand, or thereabouts, words.


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## TheRumRunner

One thing I like to do with Traynor heads that have a fan is to wire in an on/off switch for it.


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## keto

Forgive the fuzzycam but how the heck do you remove the power cord retention/strain relief piece? I've pulled and pried at it in a few different directions but I haven't figgered it out yet.


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## nonreverb

I use a set of needle nose Vise Grip pliers


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## keto

And pull in what direction? Does it come apart? Or just destroy the thing


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## jb welder

Strain relief: there are special tools for this but you can do it without them. In your photo, you would squeeze it together and push it out so it comes out the underside. Pulling on the other side of the cord might help it along. Pliers, vice-grips, I use channel-locks.
Rumrunner mentioned a switch for the fan, as you are bypassing the ground switch, there's a good use for it.


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## keto

What an excellent idea on the switch/fan, thanks!


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## keto

Like so?


I did get the strain relief out, and the new cord in with the strain relief on. Thanks.


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## jb welder

That looks good except in modern amps the black goes to the switch first, then the fuse. I'm not 100% sure but I believe this is because a user will at least turn off the power switch before checking the fuse, but they may not unplug the unit.
Then you can also consider whether you want the fan to be available when amp power is switched off, fused via the main fuse, or fused with it's own in-line fuse.


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## Rski

Cleaning the tube sockets would be my first item. Use contact cleaner on the tube pins, insert a few times, the power tube pipe cleaner works. That wire with a burn isn't any concern, the burn is facing up, no worries.

Those old cards I adopted using in my builds, the cardboard donot use any spray, air only. The problem with the cardboard is during high humidity in the summer, the amp could start sounding weird, one of my builds did, so I resorted to letting the summer sun dry out the components, the damp mens den aggravated that issue. 

The potentiometers probably need cleaning, good ole WD 40 with the red tube supplied will hopefully restore the dodgy dail if needed.

Great find...though


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## keto

One thing about justradios - don't be fooled like me and think his shipping is any sort of expedited, it's just regular mail. Cost me $7.90USD and cost him $2.35CDN. Got the stuff today that I ordered on the 13th. Onward we go, cap job ahoy.


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## loudtubeamps

Rski said:


> Cleaning the tube sockets would be my first item. Use contact cleaner on the tube pins, insert a few times, the power tube pipe cleaner works. That wire with a burn isn't any concern, the burn is facing up, no worries.
> 
> Those old cards I adopted using in my builds, the cardboard donot use any spray, air only. The problem with the cardboard is during high humidity in the summer, the amp could start sounding weird, one of my builds did, so I resorted to letting the summer sun dry out the components, the damp mens den aggravated that issue.
> 
> The potentiometers probably need cleaning, good ole WD 40 with the red tube supplied will hopefully restore the dodgy dail if needed.
> 
> Great find...though


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## keto

No worries, I got Deoxit (Sp?)


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## keto

OK, that didn't go so well! But nobody got hurt.

I will get no marks for neatness. I didn't want to pull the board, so I snipped component ends and attached the new components to the old ends.

Well, I replaced the electrolytics, including this one that I actually don't see on the schematic but it was in the amp and definitely original.


As per a suggestion I read, I put in 2 resistors in place of one, ran an end to each tube socket individually, and removed the bridge between sockets. Additionally, the bias circuit is on the right - the resistors tested fine but I replaced them (and the caps) anyways, with higher wattage rated resistors.


I put in a new power cord, and wired it as per this diagram.



And I replaced the big caps. I kept the retainers from the old big cardboard caps, and just zip tied the new caps down.


So, I plugged it into a cab, and turned on the power with no tubes. Fuse did not blow. Some noticable hum.

Put in the old Sylvania 6CA7's into my Bias-Rite, plugged that into the amp, and some misc old preamp tubes. Let it warm up, turn off the standby and snap crackle pop smoke sparks blown fuse, nope that did not go well but the tubes were suspect.

Put in a new fuse, no tubes, turn on power, lights up fuse does not blow.

Put in some JJ EL34's. Standby off, no smokeshow. Plate voltage reading 400, which is low should be ~520. Can't get a bias reading, meter shows 1.----. Within a minute, the tubes are redplating. Fuse did not blow. Noticable hum. Turned it off and here I am, not sure where to turn next.

Cap cans?


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## jb welder

Do not install the power tubes again until you have proper bias and plate voltages. You can leave the preamp tubes in. With power tubes out, check pin 5 for bias voltage. Should be -46V or whatever is shown on the schematic you are using. Without proper bias, the power tubes will red plate and the fuse will blow. 
It looks to me you have the bias caps in backwards. This is a common mistake. Because the bias voltage is negative, the + end of the bias caps go to ground. That may be the cause of the redplating.
After you get proper bias on pin5 of the sockets, check plate voltage. It may have dropped a lot due to red plating, but I think there still may be other issues.


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## keto

That could be true - I admit I was confused about the polarity of the old electrolytics. I first thought the black band has to be negative. But on the one cap, the + is very close to the black band, and they have a grooved rim on the bottom, so I thought maybe *that* was the indicator for negative. Even by that standard I screwed up and the 250uF in the tone stack would be backwards, but could actually be correct.

So, if the black band is universally negative, then yes I have the bias caps in backwards *duhrr*.


To measure the bias voltage with no tubes, do I still take it out of standby?

Any chance I've cooked the bias caps?


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## jb welder

Yes, without the power tubes you can take it out of standby to check voltages.
The bias caps may have fried if it was more than a few seconds. Is there any bulging of the bodies or at the ends?
If not, you may have got lucky. The 250V rating probably helped.


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## keto

OK -41 on pin 5. Is that too cold or too hot, the negative is throwing me. 560v on the plates LOL. The hum is greatly reduced, although there is still some present...at the lower end of audible.

If I redplated the tubes previously, can I still use them for bias checking? See below, it's the same set as previously used and redplated.

Now, the tubes are still seeing way too much voltage. Weber bias calc, class A, 560v, says 41ma, but they're seeing like mid 70's. I suppose what I should really do is put in a pot (in line with the 15K I'm assuming? It's R32 in this schem http://www.0rigami.com/vb/traynor_bassmaster_mkii_yba1a.pdf ). Or suggested next step?


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## jb welder

-41V seems to low there, should be more negative like the -46 shown on schematic. Is that the voltage with the power tubes out?
If it get's more negative with power tubes out, then probably a bad tube. If still -41V with power tubes removed, then something must be wrong with the bias circuit. Can't see R31 clearly, is it 47K? Make sure R33 is 150K, lift one end to measure.
A bias pot would go where R31 is but get the circuit working right first. Something like a 50K pot in series with a 22K would replace R31.
If all the resistors check good, and it still won't give more than -41V with no power tubes, those new bias filter caps probably got damaged when they were reversed.

P.S. The higher the negative bias voltage (more negative), the lower the idle current will be, so tubes run cooler. (more negative = colder bias).


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## keto

Thanks. -41v is with the tubes out, I didn't measure with tubes in. That thing is a beast to flip over lol.

R31 is 47K, it's one of the resistors I replaced. I'll check R33 tonight.

Thanks for all your assistance.


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## keefsdad

parkhead said:


> Keep in mind this is the internet so this is INFO -TAINMENT
> 
> I am assuming you will get the amp up and running if you service all of the components that are overdue
> 
> Though many assume I am some sort of tech I am not and I always defer to wisdom of those who have more shocks that I
> 
> While I am not a tech I an not a noob to this toob amp thing ... unfortunatly having many years of experience in these matters
> 
> (panicked people)
> 
> 99% of the time time the owner makes two assumptions
> 
> A: its just dusty have a look see, it can't be more than your minimum bench fee... in fact I really believe this will be one of those
> 
> feel good experiences where you turn to me and say Justa a loose bolt no charge ... RIGGGHT????
> 
> 
> B: oh my GOD I have blown a transformer ... its gotta be a transformer ...or some other expensive part ... this is the END OF
> 
> THE WORLD ....
> 
> in scenario B it's always a Bad Patch cable, Dead Battery, loose input Jack, pot turning and grounding out ...loose euro plug AC
> 
> cable is #1... batterys #2... Patch #3
> 
> in scenario A its always ... really DUST how 'bout some basic service since you have had this 20 years
> 
> this Leads to Parkheads #1 rule of Diagnosis
> 
> Start with the cheapest components first ...
> 
> anyway all this talk about the proper way to do things is not fun lets talk about making that sucker scream ....
> 
> get her working and have some FUN
> 
> p


Yeah, it's a great old amp, and I'm sure it will sound amazing when you get it working!


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