# 78? Traynor YBA-1



## sammyr (May 7, 2013)

Hi everyone,

I just got my hands on what I think is a 78 yba-1. I haven't had a chance to really go over it and im not too knowledgable about the yba's and was hoping for some helping ID'ing whats stock and what's not and whether or not this is a yba 1 or 1a or who knows what. I've got some pic's attached the bias pot I would imagine isn't stock and it doesn't appear to have a choke. It's even got a little mustard in there :smile-new: I'll try to update with more/better pictures a little bit later.

First impressions, this thing rocks! It crunches up pretty fast and the bass isn't as loose as I expected (my other amps are a modded silverface bassman and a metal panel marshall 1986 which can get pretty flubby/farty) 

Thanks for any help getting to know the circuit behind this bad boy


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## greco (Jul 15, 2007)

In addition, it is interesting to me that there are a couple of tropical fish caps and 4 carbon comp resistors (that I think I can identify) in the pics.

Main thing is that is working well and sounds great.

Thanks for the pics.

Cheers

Dave


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## sammyr (May 7, 2013)

Thanks for taking a look Dave any idea whats going on there with the bias pot shouldn't there be two electrolytics in the bias circuit


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## Lincoln (Jun 2, 2008)

I like the way the top comes off the cabinet to relieve the inner chassis. Good idea! Nice amp


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## greco (Jul 15, 2007)

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## sammyr (May 7, 2013)

Thanks dave I'm going to have to take a closer look at the way that bias pot is wired and see what resistance it is among other debugging. I've got some coupling caps coming from valvestorm I can get some bias supply caps from partsconnexion and then I'll be off to the races. 

and lincoln your absolutely right the pop top is fantastic its going to make biasing a breeze

edit: it looks like the eletrolytic cap in the bias supply is 68uf which i guess they threw in becuase its close to the 80 in that diagram and im hoping that square yellow guy is the other 8uf capacitor im going to have to look for some markings or labelling on it. hopefully that solves the mystery of the missing bias supply caps lol


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## jb welder (Sep 14, 2010)

That does not appear to be the correct schematic for your amp version. Try page 5 of this pdf:
http://www.lynx.bc.ca/~jc/YBA1Schems.pdf the bias circuit seems to match what you have (aside from trimpot).

The first three digits of the serial number will tell you the year it was made, if yours is 78, it should be 807 or something similar. (8 would be last digit of year, 07 would be july). The decade is figured out by the version, controls, etc. Looking at your amp, you know it's from the '70s, not the '60s.


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## dtsaudio (Apr 15, 2009)

jb's correct. This is a late model amp, the bias circuit is the one on schematic labelled yba-1 +yba-4 + eng.

Very unusual way of getting the bias out of a non-center tapped transformer. The little yellow cap is .047ufd. DO NOT make this an electrolytic. It is an AC path. If you take that cap out bias will be zero. You'll notice the 330k resistor is actually at ground.
That 68ufd is possibly original. That would have been the type used.
There has been a few other changes, I see different carbon comps and at least 3 metal film resistors in there, and the can cap to the right is not original.
While you're in there check the values of the 470 ohm 10w resistors. I've seen these way off due to age and heat.


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## jb welder (Sep 14, 2010)

dtsaudio said:


> Very unusual way of getting the bias out of a non-center tapped transformer.


I'll nitpick here Dan and say it's only _a little_ unusual :smile-new:.
Ampeg used this type of bias circuit in their V-series amps, as did Marshall with the JCM900's.

The only difference I see is Traynor has added the 330K resistor, maybe because of the lack of ground reference when standby switch open?


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## sammyr (May 7, 2013)

Thanks for the info jb and dan this amp's going to be a fun one to work on once i get a better idea of whats going on in there but my package from valvestorm came today so I've got a good selection of nos mustard, mojo dijons and mallorys and some nos silver mica and ceramics as well. Thanks for helping me get the ball rolling with clarifying the bias system and with links to some proper schems you guys are awesome. Thanks again!


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## dtsaudio (Apr 15, 2009)

> Ampeg used this type of bias circuit in their V-series amps, as did Marshall with the JCM900's


I'd forgotten about the Ampeg's. It's been a while since I've seen one. I've never seen a Marshall with that type of arrangement. Learned something new.


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## nonreverb (Sep 19, 2006)

Every JCM 900 I get, I replace that bias cap with a better quality. The stock ones have a tendency to go bad over time. Having said that, it's a perfectly good way of deriving the bias voltage...


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## dtsaudio (Apr 15, 2009)

It is a good way of deriving bias. In the case of this Traynor, I'd be inclined to replace it as well with a good quality poly cap.


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## jb welder (Sep 14, 2010)

Yes, that cap is super critical, any problem and you lose bias, red-plate the tubes, and maybe further damage. In the Traynor pictured, it is the square yellow one. I think that is a good quality one, but check the voltage rating, I like to see 600V for those.



nonreverb said:


> Every JCM 900 I get, I replace that bias cap with a better quality. The stock ones have a tendency to go bad over time.


When those amps first came out, they had a 250V cap there. We measured more than 250V across it when in standby. The cap would go bad, loss of bias, red-plating, and blown OP valve fuse. Sometimes the fuse wouldn't blow in time to save the OT, sometimes tin-foil saved the blown fuse at the expense of the OT :congratulatory:.
After replacing with 600V, we didn't see any come back.


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## sammyr (May 7, 2013)

thanks for all the info guys I'm going to try to replace that electrolytic for good measure and replace the the dual caps as well. My only question is where can I find a 68uf electrolytic they seem to be hard to track down


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## dtsaudio (Apr 15, 2009)

http://www.digikey.ca/product-detail/en/MAL213819689E3/4257PHBK-ND/263160

I think Newark has them as well.


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## jb welder (Sep 14, 2010)

100uf would be fine there as well. And you might want to up the voltage rating to 100V to be on the safe side.


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## sammyr (May 7, 2013)

I've replaced the dual can caps and I finally got around to getting that electrolytic for the bypass. Do you guys know how to throw a ppimv in there? I've had good success with the lar/mar but I'm a little confused as to how to adapt this to the yba with its 68k resistors (instead of 220k for a marshall) and tube socket wiring (also looks different than my marshall). 

this schematic appears to match pretty well. the schematic i have on the inside of the chassis is pretty bunged up but it a yba-1/yba-4 schematic. also there is a bias pot installed from before i got it


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## nonreverb (Sep 19, 2006)

Forgot to mention that in my post....most important, higher rating.



jb welder said:


> Yes, that cap is super critical, any problem and you lose bias, red-plate the tubes, and maybe further damage. In the Traynor pictured, it is the square yellow one. I think that is a good quality one, but check the voltage rating, I like to see 600V for those.
> 
> 
> When those amps first came out, they had a 250V cap there. We measured more than 250V across it when in standby. The cap would go bad, loss of bias, red-plating, and blown OP valve fuse. Sometimes the fuse wouldn't blow in time to save the OT, sometimes tin-foil saved the blown fuse at the expense of the OT :congratulatory:.
> After replacing with 600V, we didn't see any come back.


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## sammyr (May 7, 2013)

Thanks gents I got a 100uf electrolytic cap with a 600v rating I'll be plopping it in tomorrow and then we'll be off to the races. I'm excited to fire this bad boy and hear how she sounds with fresh caps.


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## jb welder (Sep 14, 2010)

sammyr said:


> Thanks gents I got a 100uf electrolytic cap with a 600v rating


Yikes, those are expensive!
Sorry about the confusion, we have been talking about 2 different capacitors here.
See page 5 of this pdf for your correct schematic (Yba1&Yba4): http://www.lynx.bc.ca/~jc/YBA1Schems.pdf
C20 is .047uF, yellow plastic in your amp. This is the one we were saying needs to be 600V. In your amp I think it will already be so.
C19 is shown as 64uf 64V. This is the one that should be replaced with 100uf, 100 or 150V. It does not need to be 600V, although that will work fine. If you have a parts source handy, get a 100uf of 100V and save your expensive 600V one for sometime when you need a big filter cap.


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## sammyr (May 7, 2013)

Thanks for clearing that up for me jb I do have a parts source I can get to so I can save that hv cap for something else. Thanks again for all the help getting this traynor back in order


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## sammyr (May 7, 2013)

Long delayed but I finally had a chance to sit down with a pile of schematics and layouts printed out and started doing some tinkering. I started by marshall'ifying v1 in the preamp and added bypass caps to the cathodes and did some tweaking to the tone stack caps brought down the big bass cap and the treble as well. Threw in a lar/mar master volume to try to save my poor ears and then for shits I added a push pull volume pot to have a switchable one wire/cascade mod (not very practical but wanted try it out. 

Been a blast working on this amp once I had the time to stare at the schem's (the unbyassed cathodes tripped me out im used to marshalls and fender bassmans) but once I wrapped my head around that quirk it wasn't too difficult to get it figured out. Thanks again for all your help and input gentlemen and without further ado, pics! *EDIT* HAPPY CANADA DAY! seems kinda fitting to be celebrating this amp today no?





















second edit: any ideas what to do with the slot where the ground switwch was. I found a replacement slide switch but im not sure what to do with it


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## sammyr (May 7, 2013)

I still wasn't quite satisfied and curiosity+boredom got the better of me so I rebuilt the preamp entirely using the marshall 1987 as a guideline.
Swapped out the pots for the tone stack to match but kept the 0.1 PI couplers in. 

I was able to use the ground lift switch to swap between bypass caps on the 820 cathode resistor on v2. Right now its wired to choose between the standard 0.68 uf, a 25uf electrolytic or no cap. Since I took the pictures I also reflowed the bias area and replaced the electrolytic for a new 100uf. 

I finally had a chance to really open her up and test it out today and boy is she loud but I really like the way it sounds now. The bright channel has tons of crunch and the standard channel is nice and fat. With the bright channel the harmonics just fly off the fretboard lets just say I'm one very happy camper
:sFun_dancing:

Here's some pics of the board and how everything looks. I need to do some cleaning up on the lead dress but so far no issues with hum or noise even with the channels cascaded with the push pull on the volume. Thanks again everyone who helped out with identifying the right schematic and any other advice along the way. This has been a really fun and challenging project for me. 

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## sammyr (May 7, 2013)

ill try to fix the pics later tonight i can't seem to get them right side up sorry guys


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