# 1974 YBA-1 mk II ... let the Modding begin



## copperhead (May 24, 2006)

Just scored this for $100 bucks & it's in great condition .Everything works & it Very loud & I have not notice any hiss or hum .
I has a 3 prong plug but i'm not sure if safe or correct ?
I want to turn this into a JTM or plexi & even a jcm 800 style but i didn't find much info on that mod .
so Master volume ppi,internally jumper the channels , replace the big caps & what ever mods to turn this into the Marshall beast . & some help to find the right mods
found this which is interesting 
Traynor Tweaks - Modding your Traynor Tube Amp


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## sammyr (May 7, 2013)

the traynor tweaks mods are a great way to get the most of the natural traynor sound thats in there. a yba-1a is extremely loud so a ppimv is definitely helpful in taming the beast. you can tweak the bypass caps on v1 to get a more marshall flavour and if if its still not to your liking you can tweak the tone stack values to better match your instrument. 
congrats on a great score


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## copperhead (May 24, 2006)

I GUESS first thing is to look at the 3 prong plug ?
it has 3 wires the middle (green) goes grounded to the chassis . 
Both White & Black wires go to the power plug ,the white comes from the plug to Fuse .
the Black goes to the on/off switch marked A/C . It still has that yellow cap going from the ground switch to the Chassis . is this Safe & SHOCK Resistant ....lol


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## sammyr (May 7, 2013)

I'd clip that ground cap for safety. I typically remove ground switches but if im not mistaken and i very well could be mistaken, you should be fine clipping the ground cap and leaving the ground switch in place. the ground switch just becomes a clunky expensive two terminal strip.


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## copperhead (May 24, 2006)

I wonder why this mark ii has the 3 large filter caps where most of the others have 2


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## PTWamps (Aug 5, 2016)

copperhead said:


> I wonder why this mark ii has the 3 large filter caps where most of the others have 2


The two firecrackers in most YBA1s are usually two-section caps, each containing a pair of 40uF/ 475V sections. The one in yours up by the pots looks to have only one wire coming from it. Is it a single section cap? You can tell by the writing on the outside. If so, one of the others probably is as well. And the third would be a conventional 2 section cap.


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## copperhead (May 24, 2006)

Both say MFD 80 450 volt ,Can't see whats written on the far left cap


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## PTWamps (Aug 5, 2016)

copperhead said:


> Both say MFD 80 450 volt ,Can't see whats written on the far left cap


Interesting. At any rate, they should be replaced and the amp will be much quieter and efficient. TubeStore.com has Spragues and JJ caps that can do the job. 

One other thing: If you remove the ground switch and cap (redundant once you have a 3-prong cord) the hole leaves you space on the back for your PPIMV if that's what you want. 

Best of luck....


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## copperhead (May 24, 2006)

Thanks , I need pots as well as a few other which i think they dont carry
another question 
my amp is the YBA-1A Mark II which is the 90 watt version & the 3 big filter caps inside are 80 uf i can buy a 80 uf cap but how would i mount them they are probably smaller than what im using ,it has 2 can caps that are 40/40uf so i'm wondering if i should go with all 4 50/50uf JJ style radial style the type that uses the clamp 
or the 32/32uf I don't see 40/40 uf only in the can cap but they are too costly


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## copperhead (May 24, 2006)

PTWamps said:


> Interesting. At any rate, they should be replaced and the amp will be much quieter and efficient. TubeStore.com has Spragues and JJ caps that can do the job.
> 
> One other thing: If you remove the ground switch and cap (redundant once you have a 3-prong cord) the hole leaves you space on the back for your PPIMV if that's what you want.
> 
> Best of luck....


this amp has the 3 prong cord ,now how do i correct this ? i want to remove the ground switch or something on the back to get my master volume in it's place


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## PTWamps (Aug 5, 2016)

Do you read schematics? They are a big help in determining values and the re-routing of wires. Google Image your model number and it'll be there.

Do you know the safety procedures to follow before working on the insides of any tube amp? Know those first.

Ground switch: You literally just "cut out the middleman." You'll see wires leading in from the AC cord , through the aux AC outlet, through the ground switch, through the power switch, etc, and into the PT primaries (usually also black). Disconnect the ground switch and just resolder those wires on the path they take before and after the switch. If you follow along the schematic, it is quite easy. (Sorry, I don't know your skill level -- so go to a tech if you aren't sure what you're doing).

For the filter caps, the biggest pain is finding the place to put them. If you already have can caps under the chassis, those spots can be used to mount comparable JJ's, but you may need to enlarge the holes as the JJ's are physically fatter in size. Another way is to use Sprague Atoms (the blue axial ones found in many old amps that have had cap jobs) mounted inside the chassis. These take up less room than the firecrackers but are individual caps, so you need to mount them on some type of eyelet board to keep them secure. Again, you'll either figure this out -- or else get a tech involved.

Good luck!

Edit: Sorry, one more thing: Those unconventional values (32uF, etc) that turn up in old Traynors are near impossible to find exact matches for... unless you go with the numerous cheap kind you find on DigiKey (Rubicon is one brand I see often). The better caps like Spragues, etc, all seem to come in rounded off values -- 40uF, 50F, etc. Tolerances allow some deviation (10% is common) from the exact values... and if you actually measure new caps, you'll often find even higher deviations from the marked value. In my old Fender I was forced to replace a couple of 70uF filter caps with 100V. The values on the other FCs were all exact matches. The amp runs perfectly and has no bias issues.


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## copperhead (May 24, 2006)

Sorry I have built an amp before & i am aware of tube amp safety ,draining filter caps ...that stuff .. I can read a schematic 
as for the power chord i guess you mean remove the ground switch & the yellow cap & reconnect the wires that were on the ground switch in the same order ? 
the turret board is a good ideal to replace all 5 caps


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## PTWamps (Aug 5, 2016)

copperhead said:


> Sorry I have built an amp before & i am aware of tube amp safety ,draining filter caps ...that stuff .. I can read a schematic


Okay, great. Just being cautious on my part for the obvious reasons. 



copperhead said:


> as for the power chord i guess you mean remove the ground switch & the yellow cap & reconnect the wires that were on the ground switch in the same order ?
> the turret board is a good ideal to replace all 5 caps


Yep, pretty much all there is to it. If you locate the ground switch and "death cap" on the schematic, blank them out and you'll see where the wires are supposed to go.


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## copperhead (May 24, 2006)

awesome thanks 
Anyone familiar with the youtuber Patfurlan i'd really like to pick his brain .


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## copperhead (May 24, 2006)

For the 3 80uf caps inside the chasis i was considering going with these (maybe i can use the existing clamps ) 80 uf Capacitor - JJ Electronics, 500V, Axial Lead Electrolytic
& the think removing the cans & using these the marshall style caps with the clamp & drilling holes to mount the clamp & i will enlarge the holes with a dremel .
& use these ,50/50uf Capacitor - JJ Electronics, 500V, 50/50µF, Electrolytic i cant find 40uf can style should 50 do the trick ?


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## copperhead (May 24, 2006)

In this Video they use the use 50/50uf & a 32/32 uf in place of the 2 40/40 uf can caps ,its a YBA-1 would that be the way to go ? instead of 2 50/50uf caps


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## PTWamps (Aug 5, 2016)

When I bought the blue Spragues for a couple of Traynors I repaired, labelled 40uF on the outside, I was getting meter readings of 46 - 50uF for each of them. Which is to say, tolerances are so wide even on these highly favoured caps that by going with 50uF caps in place of 40uF, you're probably going to be fine. People who replace filter caps without testing each one individually like I do, are probably running values as much as 10uF off spec, without even knowing it. 

For my own experience, it is rare to be able to do a complete cap job on any old amp where every new cap matches the old cap values precisely. The type of improvising you are doing is fairly normal, as caps today are simply not as widely varied as they were when everything from your radio to your Mom's Bontempi used them. Even manufacturers were wildly inconsistent at times. This past weekend I recapped a pair of almost identical 69 dripedge Bassmans. Both had the original bias caps, both different brands and values. One of them 50uf/ 50v; the other was 50uF/ 70V. If Fender could get away with such variations, I'm sure we can too. 

The Marshally JJs would probably do the trick -- since you mentioned Marshallizing the amp anyway. 

The internal clamps might not fit -- those old firecrackers have a narrower diameter than most of the new ones -- but the bolts on the chassis to which they anchor should be good as far as placement.


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## sammyr (May 7, 2013)

as a general rule of thumb I always assume that the cap value in filter caps is usually higher than the actual labelled value. eg on jj can caps the tolerance is usually -10 +30 if im not mistaken. so if you're replacing a 40 uf and you have the option of a 32 or a 50 I tend to go 32. I've replaced the mallory dynamite logs with jj multi's and used zip ties to connect the cap to the old mounting ring and then hot glue/rtv to hold them in place. it's not pretty but it can work. but if you've got a dremel id mount them permanently.


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## nonreverb (Sep 19, 2006)

The reason they're 80uf @ 450VDC is that this amp uses series/ voltage divider circuit to get 40uF along with the 100 KOHM resistors. The result is they get 900VDC rating. The two aluminum extruded can caps are the other half the the divider. This is something you might want to keep in mind when replacing them. Yes, the Spragues are rated @ 500VDC BUT if B+ is anywhere near that (and with today's 125VAC mains voltage it might be)....you don't want to have them too close to the rated voltage.....might not last too long.



copperhead said:


> Both say MFD 80 450 volt ,Can't see whats written on the far left cap


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## PTWamps (Aug 5, 2016)

Sammyr and nonreverb: Both good tips when working on these old Traynors. Thanks.


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## copperhead (May 24, 2006)

First thing I'm going is to add the PPIMV control 
but I'm not entirely sure how to wire it I've located the 2 100k resistors (which i'm suppose to remove ) & I've located wires coming from the tubes pin 6 

http://www.kilback.net/Traynor_Tweaks_rev12_sk2007.pdf
on the pot side i was following this ppimv diagram here 

Not sure how to do this as the capacitors & the wire from tubes are together on the board


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## PTWamps (Aug 5, 2016)

Page 5 and 6 on this PDF may be helpful, with a diagram showing the modified schematic. http://www.kilback.net/Traynor_Tweaks_rev12_sk2007.pdf


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## copperhead (May 24, 2006)

That PDF what I'm using basically on page 5 it shows 220k resistors for R23,R24 which mine are 100k
so couldn't we use those on the board ? as well as the grid wires that come from board .there all solder , to the .01uf bright yellow caps that is on the board .
found this ,though it's not a yba1 , thought could be just as simple 
Vintage Traynor and Garnet Amps Thread


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## copperhead (May 24, 2006)

PTWamps said:


> Page 5 and 6 on this PDF may be helpful, with a diagram showing the modified schematic. http://www.kilback.net/Traynor_Tweaks_rev12_sk2007.pdf


THE DIAGRAM in the pdf whats the that blue dotted line ? through both sides of the pot ?


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## PTWamps (Aug 5, 2016)

copperhead said:


> THE DIAGRAM in the pdf whats the that blue dotted line ? through both sides of the pot ?



I believe that blue line is for the ganged pots, to indicate how both move in tandem. Otherwise it would look a bit like there was 2 regular potentiometers side by side. 

The job you posted above looks simple and clean. I'll look at my schematics to map out quite what he's doing there.


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## copperhead (May 24, 2006)

Thank you 
if i were to follow the directions from the traynor tweaks if figure i would lift one end of the yellow .o1uf cap (c12,c13) on the end towards the tubes where they connect with r25 & r22 , thats where i would insert this ppimv 
i wonder what the pinout is for this pot dual Alpha pot ? i may be confused about that


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## PTWamps (Aug 5, 2016)

Okay, I spent some time with this. So, the YSR guy basically did what your diagram posted 3:48pm yesterday shows. Only difference is he uses eyelets on the board (probably left over from the removal of 220k resistors or whatever were there) to connect his centre pot lugs with the V4/ V5 grids. He needs to do this because he's got shielded cable so can't separate the wires they way it's shown on your 3:48pm diagram. That diagram can't use shielded cable because the black and red wires are split apart.

On my 1975 YBA-1, I have 68k resistors where you have 100Ks and Traynor Tweaks (the PDF) has 220Ks. Tweaks leaves his in, contrary to the diagram above that removes them. It looks like Tweaks would have pulled his 0.1 caps from the eyelets they share with his R22 (82K) and R2 (100k) resistors on the tube side of the board, and inserted his Ken Fischer circuit right there. Tweaks takes nothing out, just adds his ganged pot and hangs his two new .01 caps and 100k resistors off of the lugs P2P style.

Tweaks maintains that he needs that extra pair of 0.1 caps to "of course... block DC from the pot" -- but the neither the diagram above nor the YSR guy seems to bother with them. So that part of it I don't understand.



copperhead said:


> Thank you
> if i were to follow the directions from the traynor tweaks if figure i would lift one end of the yellow .o1uf cap (c12,c13) on the end towards the tubes where they connect with r25 & r22 , thats where i would insert this ppimv
> i wonder what the pinout is for this pot dual Alpha pot ? i may be confused about that


Yes to the first part.


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## copperhead (May 24, 2006)

I've followed the tweaks version & it works quite well , I also replaced the 3 80uf caps with new JJ 80uf & old dynamite sticks were mostly close to spec except one being about 106uf .
I will replace the cans in a couple of days , replaced the 470k pots with 1 meg push pull & i think i may sound a little bassier ,the yba-1a has 470k pots not 4 meg pots ..
cascading channels on vol 1 push/pull i may add the .68 uf cap "plexi mid boost" to the other push pull 
hopefully i get time to do some more tomorrow


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## PTWamps (Aug 5, 2016)

Interesting to know the Tweaks version works well. I might try this on my own YBA-1, though I'm thinking about relocating the High Range Expander (presence) to the back and putting my MV pot on the front. 

Or I might just leave it alone and build a YBA clone in a new Hammond chassis where I can do the layout as I want and be able to switch certain mods in and out. 

Been good haggling through circuits with you, Copperhead.


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## copperhead (May 24, 2006)

It's been fun ,
I do notice the controls don't really do much ,the bass control is more noticable but the treble & mid & presence is not that noticable through out the sweep


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## PTWamps (Aug 5, 2016)

copperhead said:


> It's been fun ,
> I do notice the controls don't really do much ,the bass control is more noticable but the treble & mid & presence is not that noticable through out the sweep


Do you mean that the effect of the tone controls has been diminished by the addition of the PPIMV?


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## copperhead (May 24, 2006)

I don't think it has any thing to do with the PPIMV 
I notice even before i did any mods or replaced the caps that the treble ,middle or Presence they all work but don't really have a large impact on tone on other words on 1 to 10 there is not that big of difference like some amps .


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## jb welder (Sep 14, 2010)

PTWamps said:


> Tweaks maintains that he needs that extra pair of 0.1 caps to "of course... block DC from the pot" -- but the neither the diagram above nor the YSR guy seems to bother with them. So that part of it I don't understand.


I don't see a schematic aside from the tweaks pdf and I won't discuss layouts without accompanying schematic. 
For the tweaks pdf, the coupling caps from PI block DC to the pot. This must be the case for the other versions also. At the power tube grid end of the pots would be the negative DC for the bias. You want to block this DC from the pot so you don't alter the bias when you adjust the master.


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## PTWamps (Aug 5, 2016)

jb welder said:


> I don't see a schematic aside from the tweaks pdf and I won't discuss layouts without accompanying schematic.
> For the tweaks pdf, the coupling caps from PI block DC to the pot. This must be the case for the other versions also. At the power tube grid end of the pots would be the negative DC for the bias. You want to block this DC from the pot so you don't alter the bias when you adjust the master.


Okay, I see. So in effect without those caps your master volume would act more like a bias pot?


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## PTWamps (Aug 5, 2016)

copperhead said:


> I don't think it has any thing to do with the PPIMV
> I notice even before i did any mods or replaced the caps that the treble ,middle or Presence they all work but don't really have a large impact on tone on other words on 1 to 10 there is not that big of difference like some amps .


Thanks for clarifying. On my YBA-1, the entire tonal response improved when I clipped out the little 0.001 (C5) brightness cap for Channel 2. Tweaks replaces his with a 120pF (the cap is at C3 on his amp).... but I simply took mine out. Especially for guitar, that Channel 2 was so ridiculously bright it rendered both the treble and presence pots almost useless. Clipping that cap makes the tonal response of Ch.2 more like that of Ch.1. You may not want that, but for me it works beautifully when bridging channels -- nice and fat, still as much treble response as any other amp; and my tone controls now do a lot more.


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## copperhead (May 24, 2006)

I've replaced the other can caps today & now I notice a little more hum , the hum gets louder when i turn the volume up . its pretty darn quiet with all volumes at 0


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## sammyr (May 7, 2013)

If the volume control affects the hum it would be reasonable to assume the issue lies somewhere before the volume control. Do you know the frequency of the hum whether its 60 cycles or 120hz? this can help isolate the problem. 

Since the hum appeared after the recap I would check the grounds on the caps and make sure all the connections are sound. As well look at your wire routing and see if anything has changed. You can also try pulling preamp tubes one at a time to see which area of the circuit is the noisiest. As well, depending on where the mv is placed it can pick up noise. The other thing you can do is clip a known good capacitor over the new filter caps and see if that kills the hum (this trick can be useful for finding bad caps).


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## jb welder (Sep 14, 2010)

PTWamps said:


> Okay, I see. So in effect without those caps your master volume would act more like a bias pot?


Without seeing the whole schematic I can't say for sure. I would think it will impact the bias somewhat as you are changing the resistance of the power tube grid circuit as you move the master. If it had a major impact on the bias, I would think they would have revised those mods.
If nothing else, it will keep DC out of the pot, which I think would make the master 'scratchy' when moved.


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## copperhead (May 24, 2006)

Strange thing is that i can get rid of probably all the hum by moving around ,or finding a spot in the room where the hum is at its minimal . it did all the playing with this amp at my feet on the floor which wasn't a problem before ,now if i stay kind of the the side of it there is very little hum ...


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## copperhead (May 24, 2006)

SO FAR I've replaced all the filter caps 
-Added the PPIMV 
-Changed 500k pots to 1M push pull pots 
-replaced the bright cap with 120 pf silver mica cap 
-cascade channels in vol1 push pull 
-.68uf cap "plexi mid boost" parallel with the cathode resistor -on vol 2 pull control --love the mids & slight gain this adds 
-Replaced 100k mixing resistors with 220k
-Tone stack shift – replaced .01 & .1 caps with .022 caps .used sprague orange drops 
-Tone stack shift – replace slope resistor with 33K & replace 320pf cap with 500pf silver mica cap 
Did I miss anything ? anything else ...THINKING playing with the feedback resistor 100k stock ? 
The tone is a little on the bassy side but using a boss SD-1 as a clean boost really turns this into an awesome sounding amp with strong mids & tightens up the tone .very Marshall like ..I love it with the overdrive pedal .
at the same time & really nice tones the treble tones are almost harsh sounding ,clean or dirty they are quite bright on the high E & B string .
one thing I have not tried was swapping the stock tubes ,Not sure but they could be all original .
Westinghouse 6ca7's 
V1 has Sillvania 12ax7
V2&V3 Philips 12ax7's 
as i said in my previous post I getting some hum or interference that I've not noticed befere changing the last as can caps ,but if you move around with the guitar you can pretty much eliminate it


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## PTWamps (Aug 5, 2016)

Nice list of mods. Watch those old tubes (yes, I think those Westinghouse 6CA7s are original). My amp conked out on a gig when the old power tubes finally packed it in. The amp won't turn on at all when they go, so you'll know. Stuck in a pair of Ruby El34s I had on hand, but my plan is to order up a pair of JJ 6CA7s by the time next summer's gigs come around.


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## copperhead (May 24, 2006)

whats the deal with power tubes for this amp . I know i bought this from the original owner .
This is the Beast YBA1A mark 2 90 watt ,I don't want to look for NOS 6ca7's if i have to pay an NOS price ,I'd rather go with a modern tube like ` the el34l 
if they don't make a modern 6ca7.
something that withstand the 560+ plate voltage


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## PTWamps (Aug 5, 2016)

Get the JJ 6CA7s from TubeStore. Affordable and they'll withstand a Traynor as well as anything. Running 90-watts on a pair of 6CA7s is nuts -- is there only a pair in your amp?. www.thetubestore.com - JJ 6CA7 Audio Tubes

I have one of the late Silverface Super Reverbs that runs 70-watts on a pair of 6L6s, which is equally nuts. That amp used to eat tubes for lunch until I put in JJ 6L6s three years ago, and they've been fine since.


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## copperhead (May 24, 2006)

Thanks & There is only 2 power tubes


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## nonreverb (Sep 19, 2006)

If this is indeed the venerable YBA-1A, you're going to go through new production EL34 on a fairly regular basis. The plate voltages are really high and combined with slightly higher mains voltages now, it's even harder on them. You might try upping the value on the screen resistor by separating the single resistor to two separate 1Kohm 5watt ones. ( a much better option IMO). Even with these mods, I find new production stuff just doesn't do so well in these high plate voltage amps. 6550's might be an option for reliability though.



copperhead said:


> whats the deal with power tubes for this amp . I know i bought this from the original owner .
> This is the Beast YBA1A mark 2 90 watt ,I don't want to look for NOS 6ca7's if i have to pay an NOS price ,I'd rather go with a modern tube like ` the el34l
> if they don't make a modern 6ca7.
> something that withstand the 560+ plate voltage


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## sammyr (May 7, 2013)

+1 on what nonreverb said. On almost all of those old traynors its never a bad idea to split the single screen resistor into separate resistors for each tube especially on a 1a with that high voltage. 

One of the more knowledgeable fellas can correct me here if im wrong. but you could probably knock the b+ the down to a more manageable level with some zener diodes in series with the PT center tap. It will change the tone and feel of the amp im sure but in conjunction with the separate 1k screen resistors you could probably save some wear and tear on new production tubes. You'd have to check to make sure the zeners are the right rating and won't overheat but I found an example on the marshall forum where someone used a turret strip to mount the diodes and shave 80 volts off his yba-1a's b+.


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## jb welder (Sep 14, 2010)

A heatsinkable high power zener on the chassis is also another option. The above uses that many 5W zeners to handle all the power that needs to be dumped as heat.

As far as the higher modern line voltage goes, I always like to check what the heater voltage is running at. If it's too high, reducing the voltage at the primary side of the P.T. should be considered. This can be done with a bucking transformer. See RG Keen's 'vintage voltage adapter'.
This will also knock down the B+ somewhat.


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## nonreverb (Sep 19, 2006)

The bucking transformer is a good idea.....The zener option will work as well but it's unfortunately reverting the amp back to a YBA-1 in a way. Part of the YBA-1A's distinctiveness is it's higher power and consequently different sound and response.....albeit LOUD!!



jb welder said:


> A heatsinkable high power zener on the chassis is also another option. The above uses that many 5W zeners to handle all the power that needs to be dumped as heat.
> 
> As far as the higher modern line voltage goes, I always like to check what the heater voltage is running at. If it's too high, reducing the voltage at the primary side of the P.T. should be considered. This can be done with a bucking transformer. See RG Keen's 'vintage voltage adapter'.
> This will also knock down the B+ somewhat.


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## copperhead (May 24, 2006)

Wow ..decisions decisions .. Thanks lets keep this thread going as i do some research on the zener diode


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## copperhead (May 24, 2006)

Modded to the JCM specs now ,Still got a little work but I must say this thing sounds killer .my ears are ringing .it has lots of gain now .not really much hiss but so i will possibly be adding 100pf cap on v1 few things i need to check out , my PPIMV now turned all the way down is fairly loud ,if you turn it up it gets louder .that's something i will look into .a few minor details .


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## copperhead (May 24, 2006)

Something that i kind of forgot about is the small electrolytic capacitors on the board ,some of these tested way out of spec reading incredibly high (especially the dual cathode sets from V1 )
Even though all filter caps replaced in both of these amps (my yba-1 & Mark II) I think the old Mallory's were still doing there duty even after 40 years ....Must of been quality caps


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