Lowering the Voltages on a Traynor YBA-1

[boy howdy]

I have a '68 YBA-1 (has a choke, SS rectifier, and EL-34s), which as you probably already know is very similar to a tweed Bassman or JTM-45. But of course a Bassman/JTM-45 that's been optimized for bass. The voltages are on the high side.

I'm new to the subject, so I'm looking to get a bit of education here.

Starting voltages were:

with R31 @ 4k7 and R32 @ 10k:

V1 pin 1 - 232
V1 pin 6 - 236

V2 pin 1 - 350
V2 pin 6 - 208

V3 pin 1 - 264
V3 pin 6 - 278

V4 pin 3 - 450
V5 pin 3 - 455

Current voltages (no pun):

with R31 @ 22K and R32 @10k:

V1 pin 1 - 172
V1 pin 6 - 173

V2 pin 1 - 258
V2 pin 6 - 153

V3 pin 1 - 193
V3 pin 6 - 205

V4 pin 3 - 439
V5 pin 3 - 442

Are these voltages okay? They seem a little low compared with most of the voltage charts I've seen. But then some Marshall charts I've seen are all over the map, with both higher and considerably lower voltages.

If you'd care to, I'd love to hear from you guys what effect I'm supposed to be hearing, if any, by lowering the voltages. I'm not at all sure I hear any difference at all.

Thanks, guys.

[Firestorm]

what are you trying to accomplish? Based on the available YBA-1 schematics, I'd say your starting voltages look pretty much spot on. If you do want to manipulate preamp voltages to "brown it out," the dropping resistor you really should play with first is R32 rather than R31. R32 sets the supply voltage for just the preamps; R31 also controls the voltage for the PI. If you drop that you'll reduce its gain and kill its headroom. To hear the difference in supply voltage tweaks, you pretty much need to crank the amp.

[billyz]

They look good to me. I usually install 1k 5w screen resistors . And 1 meg volume pots when the 5m pots get bad. An adjustable bias is usefull too. New power supply caps and your good.

[boy howdy]

Yeah BillyZ, already got all of that in place. Pretty happy with it, as in very happy.

Someone somewhere somewhen said that high voltages don't sound as good for guitar, so using a JTM-45 voltage chart I found online I set about lowering them.

I've tried several configurations at this point, including what you mentioned, Firestorm. I overshot just a bit from the JTM-45 chart though and wonder if it matters. I can't really hear any difference from the stock voltages and the new lower voltages though. That may be because I have to run it through an attenuator (Weber Mass 100) if I want to hear it cranked. Don't know.

If I knew what to listen for I'd know if I need to take the voltage back up or what. I think I'll probably just leave it as is unless someone says I should do something different.

[billyz]

I would not call 440 high , medium is more like it. 500+ is getting a little high. Every Carol Ann I have worked on has been over 500 and they sound really good.

[boy howdy]

Yeah well, I haven't done anything to affect the EL-34s, though they have fallen a little bit. I'm more interested in the preamp and PI voltages.

Particularly concerning is Firestorm's comment that lowering the voltage on the PI will reduce its gain and headroom. Headroom reduction would be fine (this thing is LOUD), but gain reduction would not be a good thing. Can anyone give a second opinion on that?

[boy howdy]

Yeah well, I haven't done anything to affect the EL-34s, though they have fallen a little bit. I'm more interested in the preamp and PI voltages.

Particularly concerning is Firestorm's comment that lowering the voltage on the PI will reduce its gain and headroom. Headroom reduction would be fine (this thing is LOUD), but gain reduction would not be a good thing. Can anyone give a second opinion on that?

[LeftyStrat]

Yeah well, I haven't done anything to affect the EL-34s, though they have fallen a little bit. I'm more interested in the preamp and PI voltages.

Particularly concerning is Firestorm's comment that lowering the voltage on the PI will reduce its gain and headroom. Headroom reduction would be fine (this thing is LOUD), but gain reduction would not be a good thing. Can anyone give a second opinion on that?

Given the fact that the LarMar PPI Master Volume is popular in Marshall-like amps, I don't see a problem with lowering the gain of the PI. This is essentially what the LarMar is doing, dumping gain before the power tubes.

Reducing the headroom of the PI will make it distort sooner, reducing the gain just means it won't be as loud when it is pushed to clipping.

[billyz]

It really depends on what sound you are after and exactly which YBA1 circuit you have. I have seen 3 different ones.

First, if you want more distortion then make sure V1 is bypassed. might try a .68mf cap on one side and a 22/25uf on the other. Yes separate the cathodes and use 1.5K or 820 or 2.7K to your taste. Then Bypass V2a with a 22/25uf or 10 or even 4.7uf cap , again your taste. If that is not enough , try 220K Plate load resistors on V1. I'm pretty sure that will get you there.

I think your voltages are fine even on the preamp.