Traynor YBA-1 Plexification

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Traynor YBA-1 Plexification

Postby Tman on Tue Feb 09, 2016 8:56 am

I picked up a '71 Traynor YBA-1 a few weeks ago. I've been hip to these for years but never had a chance to try one and when one popped up nearby I jumped on it. Pete Traynor designed these using a modified Bassman circuit. They are really only a few component changes away from being a Bassman or a Marshall Plexi. I did some research on the web, planned the mods I wanted to try then placed a parts order. My parts order was delayed a little over a week due to the snow storm backing up USPS shipments but the parts came last week and I couldn’t wait to get into it.

I went out in my barn at 5 am Saturday morning to do the mods to my YBA-1. It was 25 deg and I froze my ass off but it was worth it.

Here is the before picture:

Image

And the after (picture taken before I added the cathode bypass cap and changed the feedback resistor):

Image

The work done:

I installed long overdue new filter caps.

I removed the 470k linear volume controls and put new 1 meg logarithmic volume pots in their place. I used a switching pull pot for the bright channel to control some preamp changes.

I swapped the 100k mixing resistors replaced with 220k. Antique Electronic Supply was out of 270k and naturally the local Radio Shack didn’t have them either so I used the closest value I had.

I replaced a .1 cap in the tone stack with a Mallory .022, replaced the slope resistor with a 33k and swapped out the 320pf cap with 500pf silver mica. That makes the tone controls a lot more useful.

I connected a 2.2k resistor and a 22uf cap to the switch on the pull pot which connects parallel to V1B's 1.5k cathode resistor when pulled. That provides a nice gain bump when engaged and is at stock value when off.

Lastly I replaced the 100K feedback resistor changed to 47k.

Everything is working perfectly. The volume controls are no longer on/off controls and the amp has definitely shifted to the Marshall camp in the tone department.

Here’s my frozen fingers test clip through a V30 loaded 212 cab. :lol:

Les Paul straight in, no pedals at all.

Last edited by Tman on Wed Feb 10, 2016 9:15 am, edited 1 time in total.
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Re: Traynor YBA-1 Plexification

Postby Unit_1 on Tue Feb 09, 2016 7:34 pm

Sounds great Tman!

I just slapped some vintage =C= KT88's in my JTM50 plexi clone. At full volume it sounds like over 100 watts. Crazy chunky grunting break up.

And clean with my tele I'm getting Gilmour sounds. Pinch me, I must be DREAMING!
:highfive:
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Re: Traynor YBA-1 Plexification

Postby Tman on Wed Feb 10, 2016 9:12 am

That sounds like perfection. The mods are o fresh in this one I'm still discovering what it has in it's bag of tricks. I tried a few OD pedals in front of it yesterday and it love a clean set SD-1 just like my '93 1959SLP-ri used to.

Not for the faint of heart. :say_what:

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Re: Traynor YBA-1 Plexification

Postby Tman on Sun Apr 10, 2016 7:00 am

I've found my desert Island amp. No dirt pedals required, just plug in and let it rip.

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Re: Traynor YBA-1 Plexification

Postby Unit_1 on Sun Apr 10, 2016 6:06 pm

Sounds very plexi-ish! :highfive: congrats!

I'm running nos =C= 6550's in my 'circa 1967 model 1987 plexi clone with MM iron, mustard caps and I get a lot more dynamic chunk and not quite as much grind although it's certainly not timid by any means :mrgreen:

it's also through 2 x g12h + 2 x g12m so it's VERY loud. I get scolded if Ms.Unit is any where near :shock:

:jam:
Image
The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

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Re: Traynor YBA-1 Plexification

Postby Tman on Sun Apr 10, 2016 10:30 pm

:lol: I've found myself in that position before.
The attenuator helps keep me out of trouble. :wink:
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Re: Traynor YBA-1 Plexification

Postby Tman on Sun Apr 17, 2016 10:17 am

Tried it with a MIM Telecaster and a few pedals on Friday. I think I'm in love. :lol:

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