Traynor YBA-1

[jharasym]

Newby trying to learn about working on amps without killing myself, just acquired a '72 Traynor YBA-1.

Couple of questions:

- earlier versions originally had 4M A volume pots, and I've read it's recommended to change these out for 1M A pots. Mine has 500k Linear pots. What's recommended here (1) leave them as is, or (2) change them for audio pots @ what value?

- what's the story on speaker impedance - will I do any damage running non-8 ohm speaker setup (2 x 8 ohm in parallel or series, ie. 4 or 16 ohms) ?

- I noticed the caps were all drained a couple of days after operating the amp. Is this normal - were there draining resistors in the factory circuit - how would I recognize these if installed?

- what sort of MV would be recommend, pre or post PI?

Thanks a bunch

[Chuck H]

earlier versions originally had 4M A volume pots, and I've read it's recommended to change these out for 1M A pots. Mine has 500k Linear pots. What's recommended here (1) leave them as is, or (2) change them for audio pots @ what value?

It depends on what circuit you have and what you want the amp to do. There were a few different circuits for that amp. Some completely different. You can find the schematic under the hood. Take the top panel off, the schem should be pasted to the underside. Then try to find a link to a matching schem on line so that we can know what circuit we're dealing with.

what's the story on speaker impedance - will I do any damage running non-8 ohm speaker setup (2 x 8 ohm in parallel or series, ie. 4 or 16 ohms) ?

Those amps have an impedance switch on the back.

I noticed the caps were all drained a couple of days after operating the amp. Is this normal - were there draining resistors in the factory circuit - how would I recognize these if installed?

I don't know if any of the models had resistors that would drain the circuit. I do know that most caps don't hold a full charge. Some drain can also happen through the tubes when the amp is shut off. It is possible for high voltage to remain on filter caps with the amp off. So we always assume this to be the case for safety reasons. In reality there is typically less than twenty volts on the caps after the amp has sat off for a few minutes even when there are no drain resistors. NEVER assume this to be the case though. Being cavalier can kill you. I'm just saying that what your seeing is normal.

what sort of MV would be recommend, pre or post PI?

That also depends on what you want the amp to do. Even though a post PI MV can make for more distortion, it's probably best suited for vintage OD tones because it allows a stage after the EQ to be clipped. This effectively nullifies any actual EQ and makes the tone controls more like distortion character controls. With the amps final EQ being left to the OT and speakers. A pre PI MV won't generate as much distortion, but would allow you to NOT clip the amp beyond the EQ. So as long as you don't crank the amp into clipping the power tubes your EQ adjustments remain defined. This is better if you play metal because you can dial in that V notch EQ sound. Of course, you'd need a high gain preamp or pedal to generate that uber gain sound entirely before the PI.

[jharasym]

You can find the schematic under the hood. Take the top panel off, the schem should be pasted to the underside. Then try to find a link to a matching schem on line so that we can know what circuit we're dealing with.

I have the schematic- I'll try to find a match online.

Those amps have an impedance switch on the back.

No switch on this one. thought I read somewhere that these big Hammond transformers can tolerate a wide mismatch in impedance.

That also depends on what you want the amp to do. Even though a post PI MV can make for more distortion, it's probably best suited for vintage OD tones because it allows a stage after the EQ to be clipped. This effectively nullifies any actual EQ and makes the tone controls more like distortion character controls. With the amps final EQ being left to the OT and speakers. A pre PI MV won't generate as much distortion, but would allow you to NOT clip the amp beyond the EQ. So as long as you don't crank the amp into clipping the power tubes your EQ adjustments remain defined. This is better if you play metal because you can dial in that V notch EQ sound. Of course, you'd need a high gain preamp or pedal to generate that uber gain sound entirely before the PI.

I guess I'm after more vintage tones, but would prefer to maintain versatility. Where does that leave me?

[jharasym]

Here's a link to the closest schematic I could find online:
Prowess Amplifiers - Traynor - Schematics - Bassmaster Yba 1 - Version 2

There are some differences which may include drawing errors?
First info is the online schematic, second is mine:
R4&R8 : theirs 1.8K, mine 1.5K
R38 : missing, 6.8K (in series between R37 and Low Range Expander)
C8 : 0.01 uF, 0.02uF
C7 : 0.01 uF, 0.1 uF
R32: missing, 180 Ohms (from tip of speaker jacks to ground)
C15&C16 : 40F, 40uF

Some in the same position but with different labels:
C28=8uF, C20=8F (last capacitor is C22)
C29=64uF, C19=68uF
R39=27k, R31=39k (last resistor is R38)
R32, R38 (same value)

Thanks
John

[Regis]

YBA1-A's are 8 ohm output impedance.

A friend of mine fried the screen resistors running his YBA-1A into a 16 ohm cab, I wouldn't do it.

They do not have switchable impedance.


I just built a detuned 1x12 cab for mine and it rocks.

Have you played the thing much? They are pretty killer amps without any mods at all. The only thing I did was internally jump the channels.

[Chuck H]

They do not have switchable impedance.

My later model did. Didn't know the older ones didn't.

Have you played the thing much? They are pretty killer amps without any mods at all.

Absolutely. I dredged and rebuilt mine as a different amp. Aside from an OD channel the new circuit had nothing over the stock circuit.

[jharasym]

Have you played the thing much? They are pretty killer amps without any mods at all. The only thing I did was internally jump the channels.

I just got mine and am playing with it. It's of course very loud, so I am thinking about a MV. I see posts recommending an attenuator instead of MV mod, but my experience with a Hot Plate on my Vibrolux Reverb was not favourable.
I would like some more "crunch" out of it.

[g1]

Any of these schematics match? http://www.lynx.bc.ca/~jc/YBA1Schems.pdf
He also has some mods & other information & links for these amps here: Traynor Amplifier Schematic Archive

[Chuck H]

Revoice one channel and stack it in front of the other channel. Then install the post PI MV and a pre PI MV. When you want metal V notch EQ tones use the pre PI MV and run a boost or distortion for "uber" gain. When you want more vintage OD tones use the post PI MV for that saturated sound. Lots of guys have done it. There are interesting options using both in combination too.

[jharasym]

Any of these schematics match? http://www.lynx.bc.ca/~jc/YBA1Schems.pdf

Yup - last one (page 9) at http://www.lynx.bc.ca/~jc/YBA1Schems.pdf

[jharasym]

Sounds interesting. How re-voice? Do you know of a description of this on-line?
Thanks
John

[jharasym]

Revoice one channel and stack it in front of the other channel.

How is one channel stacked in front of the other ? Does jumping the inputs accomplish it, or could you direct me to a circuit description of this?
Thanks
John

[Chuck H]

It would require rewiring a couple of things. I'm working on a drawing but I need to get to work just now. Hope to post it later.

[Chuck H]

Took a break this morning and drew it up. This may not be your exact schematic, but you should get the idea. FWIW if that amp has any original electrolytic caps in it they should probably be replaced.

[jharasym]

Wow - great job on the schematic. That's a lot to absorb, but I'll work my way through it and try to grasp what each change represents. Does the first switch leave the circuit more or less original in the one position (and stacked channels in the other)?