# which vintage traynor YBA for plexi mod?



## Budda (May 29, 2007)

As the title states, Im considering getting a YBA and potentially converting it into a plexi. Which model usually gets this treatment?

My friend has a yba 3 custom special (wide beast) and it sounds huge with his bass. Another friend has a '76 of some sort with the plexi mod that im going to (hopefully) try next week.

Cheers!


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## keto (May 23, 2006)

Cheapest and easiest should be a mid 70's YBA-1, at a guess. Similar but not as good as the earlier models stock (according to some and to my own personal observation), so not as desireable ergo cheaper, and if you're having the circuit modded who cares?  It's what I should have done with my '77 when I had it a few years ago, but that was before I got into amp building. I bought it well used at L&M for like $200 or a little more 6-7 years ago.


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## traynor_garnet (Feb 22, 2006)

Yba-1 or Yba-1a. Neither will take that much of a "mod" as they are already close. If you get into changing trannies etc don't bother just get "a marshall"

TG


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## Budda (May 29, 2007)

How do the tones differ on a 68 vs say a 75? If the older one sounds good without mods at an extra $150 I'll just leave it stock and slam it with a pedal. Might add the fx loop though...


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## Budda (May 29, 2007)

Morris modded 68 YBA 3 custom special running 6550's in saint catharines, I know what I'm doing this weekend (hopefully). 

Still need to sell my Peters though...


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## parkhead (Aug 14, 2009)

all the yba-1 are good for plexi conversion. You will pay more for an earlier amp as they are already the 59 bassman jtm45 circuit. 
The bumper amps are best to mod... 70 -73. they are priced better and still have a good output transformer. Later the output transformer shrinks and the circuit gets further from the original. 

The biggest problem is identifying which Plexi circuit you want to convert to. The plexi mojo is not really in the pre amp 

p


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## Budda (May 29, 2007)

Any thoughts on the '68 YBA 3 custom special, before I make a trek?


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## bcmatt (Aug 25, 2007)

Budda said:


> Any thoughts on the '68 YBA 3 custom special, before I make a trek?


I'm sure it would work great for a conversion... but I wouldn't, because it is actually the best sounding bass amp for bass I've ever heard. My absolute favouratelate bass tone


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## Budda (May 29, 2007)

I wouldnt mod it, just looking for opinions on the tones it can get for guitar.


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## JHarasym (Mar 27, 2007)

Of course the YBA-3 is 100 watts, while the YBA-1 is 45 to 50. All of them are very loud.


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## Rideski (Feb 25, 2009)

Check this out: http://www.kijiji.ca/v-amp-pedal/ot...ab/1039357047?enableSearchNavigationFlag=true
If I hadn't just bought the new version of this head and cab I'd be all over this. No affiliation with this kijijii seller...


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## sammyr (May 7, 2013)

I have two mid seventies YBA's one YBA-1 and one YBA-4 combo. Same circuit just ones a head and ones a combo. The later ones are further from the jtm45 circuit but can definitely be modded to get some interesting tones. I rebuilt my yba-1 using a plexi style preamp but left the power section pretty well stock and added some bells and whistles for fun (ppimv, switchable v2 bypass cap, push pull for cascading inputs). I posted the process in an earlier thread on the forum here if you'd like to see some pictures for ideas and inspiration. Some might say its sacriledge but I find I really love playing it with the inputs cascaded and the master volume down low to really chunk it up but it also cleans up really nicely when you back off on the gain. Let me know if i can advise or help in anyway, these amps are a blast to work on. The guys here helped me out a ton as well so all credit is due to them  

link to thread http://www.guitarscanada.com/showthread.php?63753-78-Traynor-YBA-1/page3


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## Budda (May 29, 2007)

Sorry sammy! Damn phones.

I was all set to get the YBA3, but the lack of nibbles on the FSM makes me nervous to spend money and wait to recoup from a sale.

Im still really interested in the idea, but i think it will have to wait . I miss having cleans at home!


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## sammyr (May 7, 2013)

haha how rude! why I never! 

Keep your eyes peeled to the classifieds hopefully a reasonably priced one will come up although they seem to be getting pricier and pricier. I'm one of the lucky ones I found my yba-4 on the curb on garbage day downtown. 

Happy Hunting


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## bolero (Oct 11, 2006)

I have a stock YBA1 as well as a '60's plexi

I never bothered modding the YBA-1 it sounds great as-is. it's got EL34's though, which isn't as common as the 6L6 heads ( I think? )

they both take pedals really well, sound very similar actually. the YBA-1 stays a bit cleaner & sounds more Hiwatt-ish, but it get raunchy too if you crank it

cranking a 45w amp like that is going to be LOUD anyway, so I would just get a pedal


ps I sold an Ampeg SVT & 8x10 cab once I got a YBA3 & 8x10 "big B" it sounded killer for that oldschool bass sound


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## parkhead (Aug 14, 2009)

couple of things 

#1 the term Plexi is always misleading 
The Bluesbreaker was a plexi, the 1987 is a plexi... there were at least 4 different plexi models Guitar, Bass, Organ and PA versions ... and tremolo versions of each 
the Guitar circuit was revised continuously between 65 and 69 ... the other circuits stayed mostly unchanged but shared transformer and power supply revisions. 

IMHO the proper electronic definition of a plexi besides the cosmetic reference to the lexan control panel; is "any Marshall prior to the use of the 50/50 dual can filter caps" 
those amps have less overall filtering and a dirtier more spongy tone irrespective of the pre amp circuit..
The standardization of the filtering to double 50mfd cans in Marshalls started in late 68 and was complete by 1970 on all models. 
The Lexan (plastic) control panels were phased out in mid 69 as Marshall standardized things like the 50mfd cans. 
I talk to many people who think any JMP style Marshall is a Plexi and others who think any Marshall with 4 inputs is a Plexi. 
When I was buying Plexi amps I always looked for the earlier filter setups as an indication of the true desirability and potential tone of the amp. 
Amongst my old Marshalls the best sounding units are the ones with the most primitive filtering setups... including a throwback 1969 Metal front 1985 PA head 
that just defines that early ZZTOP raw Marshall tone. Being a PA head it is closer to a tweed bassman circuit than anything other than a 65 JTM45. 


Another great example would be the EVH plexi which features the very aggressive and bright lead circuit (about 7 pre amp changes vs the original JTM amps ) 
but has the power supply and filtering of the much earlier amps ...allowing it to be both very high gain and very dirty and "BROWN" sound 
Marshall made very few of these before they started building up the filtering to increase the headroom and punch... at the expense of the softer Brown tones

The first Traynor YBA-1's are a close relative of the earliest JTM style Marshalls sharing a lot of circuitry with the tweed bassman. 
The primary difference is that Pete Traynor was trying to build bass amps and immediately realized he needed more headroom and LARGER TRANSFORMERS 
Larger Transformers tend to make an amp sound bigger and louder all else being equal.
Pete realized that one of the keys to greater headroom was increasing the amps power supply filtering ...so all bassmasters have 40mfd filters for the mains and screens 
while marshall used 32mfd for the mains and 32mfd or even 16mfd for the screens (on 100 watt plexis) until 69 when they bumped all filters to 50mfd cans ultimately using 6x double 50mfd cans 
to double the voltage handling and ensure 50mfd in all filter nodes including the mains screens and pre amp
IMHO all of these Marshalls sound horrible compared to the real plexis which have less filtering overall and tend to use combinations of 32mfd and 16mfd cans. 
(the reissues all use 50/50 cans and don't sound like the old amps) 

Which brings us back to doing a Plexi conversion or more properly preparing a YBA-1 for guitar duty 
If you simply brighten the Pre amp Marshall style you will not get a plexi sound, you will get a 70's or reissue sound. 
YOU NEED TO REDO THE POWER SUPPLY to get the REAL sound! 

If you get an early YBA-1 amp you are almost home free since the circuit is already 90% 59 Bassman. 
It has been my experience that in most cases the Mallory 40mfd filter cans are now nearing the end of their lives.
Worn out Bias supply caps are the cause of 99% of YBA-1 Problems and these amps become 100% reliable with fresh electrolytics. 
So your best approach is to find a very good tech and have him replace those filters. 

Since you pretty much NEED to replace all electrolytics to make these amps reliable for regular use you can tweak some values. 
For a better guitar tone here are some value tweaks for new filters. 

Mains leave as stock, 40mfd, or you can upgraded to 50mfd or even slightly more. I use a double 32mfd can and jumper the terminals to get 64mfd for the main B+. 
Be aware that adding MFD can quickly harden up the tone and make the amp really harsh. 
The main B+ is the best place to add any filtering to reduce noise, having minimal impact on the pre amp voice. 
Beyond the B+ filter adding MFD will typically impair your tone and add harshness. 
If you want to experiment yourself go ahead... you will find over filtering the any amp a pretty frustrating experience as the "good sounding" distortion 
and harmonics move further up the dial towards 10. 

If the amp has a tube rectifier and you want to hear the authentic bouncy 59 bassman sound use 40mfd for the main filter. 
For the screen cap I reduce the filtering to 16mfd, 20mfd or max 32mfd. (add filtering here and things get ugly and harsh FAST) 
Fender used 22mfd on the bassman and Marshall used only 16mfd on the early 100 watt plexi (2x32 stacked to double their voltage handling) 
For the bassman sound go with 22mfd ... for the raw early plexi sound get the screen cap down to a nice brown 16mfd (just trust me on this ... ) 

continue to replace the filters with bassman or plexi values to get those sounds 

Traynor used 8mfd or 10mfd for the whole pre amp and you should stick with this value like the 59 bassman.

if the amp is still too bass oriented heavy you can change the 150mfd or 220mfd V1 bypass cap to 10mfd or 6mfd 
If you want the authentic bassman or JTM45 wooly THUNK stick with 220mfd ...
Leo was a genius he used the 8mfd pre-amp filter to limit the bass response of the pre amp by reducing the bass response 
of the power supply filter.. played softly the bassman has huge thumpy bottom end ...pushed hard the bass is stripped out by that 8mfd filter 
its acts like an automatic eq shift protecting the speakers and limiting the bass at high volumes ... 
if you upgrade this value as Fender did on the 59 bassman reissue (40mfd) the amp becomes clunky and the bass splatters instead of compressing 

finally the bright cap on the YBA-1 is 1000pf (very very bright) 
The bright cap on a post 68 Superlead is 5000pf (painfully bright at low volumes but... having a particular sound above 6 ) 
Fender used 100pf on the bassman 
Marshall also used NO bright cap, 100pf and 500pf depending on the amp 
I favor No Bright cap which suits pedals best 

follow these value tweaks with your fresh electrolytics and you will have 
a guitar amp that is already the most beloved circuit in the world fine tuned to 
cover all of those famous sounds 


to sum up the early YBA-1's were beefed up 59 bassman's 
if you de-evolve the amp using the 50's fender specs or early hand drawn scematic JTM45 specs
you will be blown away by this beast 

and if you play really LOUD and like HIWATT type sounds the stock early YBA-1 is already there !

P


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## Budda (May 29, 2007)

Parkhead brought the goods! Thank you!

I will see about the super early ones then. I want the option of being super loud and clean, so that it's there if I need it.


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## Latole (Aug 11, 2020)

I'm reviving the topic because this is the best I've found.
For a customer who would like his Traynor YBA-1 to be modified to a "plexi". 
parkhead in your answer #16, is there anything to add to your excellent information? 

Or others who have done these modifications successfully?

The YBA- I have would be, I believe a 1969.
The pots are numbered 481 BO6837 and 481 BO6902. It mean second week on 1969


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