Traynor YGM-3 B+, B++, and Plate Voltages, Too High or Normal?

[misterc57]

My late 1960s YGM-3 voltages seem high (to me). I do not want to cook my output tubes. Not sure what a pair of 6BQ5 max voltage are.


My VDC are

B+ 397
B++ 300
6BQ5 plates 390



I am looking at the reissue factory schematic for voltage references. The reissue uses (3) 32 uF caps in the power supply filtering, my amp uses (3) 40 uF.

The reissue VDC are

B+ 372
B++ 268
6BQ5 plates 367



Is it a concern? Tube specs indicate 300 VDC max on 6BQ5 plates, yet even the reissue shows 367 at the plates.


I can reduce B++ with higher value dropping resistor, I got B++ down to 273, but then my 6BQ5 plates go up to 406.

Thank you. MarkO

[Chuck H]

Your amps stock voltages look about right to me. Traynor probably reduced voltage on the reissue for their own reasons, but the originals always run closer to 400Vp. el84's aren't great with that and tend to wear out or become microphonic a lot faster than when more conservative voltages are used, but a lot of people did it. Including Mesa, Fender (in two different eras), Peavey and others. They're cheap after all.

[Dave H]

Schematic says B+ 400V, Plate voltage 398V

Traynor_guitarmate_ygm3.pdf

Edit:simulpost

[misterc57]

What about the V5 12AX7 plates? Those seem excessive high also?

I have 375 VDC.

Thank you

[g1]

Using the schematic from post #3, what is your DC at supply node after the 470R ?

[g1]

Never mind, you have the reverb transformer and probably the supply is more like the YGM1. Reverb driver voltage will be similar to standard Fender, pushing 400V.
So there is not much drop between B+ and V5 plate, 375V doesn't sound far off.

[misterc57]

I have been experimenting most of today with voltages and different resistors.

My VDC are now

B+ 399
B++ 234
6BQ5 plates 396

Regarding reverb transformer and V5. I dropped V5 plates to 268 VDC (from 375). Would this cause any problems? The reverb still works and seems more responsive now in that there is a larger range of reverb, nothing useful after 3 or 4 on the pot.

I'd be fine going back to 375 VDC. I was just concerned about it being to high a voltage and burning up the tube.

[g1]

If you like the sound with the lower voltage then you are good.
But you don't need to worry about the voltage. Like I mentioned, classic Fender BF circuits run the 12AT7 at 400 volts in the same type circuit. 12AX7 has the same voltage limits as the 12AT.

[misterc57]

Thank you all for the help!

[66 Kicks]

That redrawn schematic is really bogus. I added up the current going across the 22K dropping resistor and got 2.87mA. 2.87mA across a 22K resistor would be 63V, but he is dropping 170V. He is dropping 10V across a 470r dropping resistor for 21.3mA, but the reverb driver alone is pulling 22.7mA and then there are the screen and preamp currents. I drew you up a couple of schematics with what I consider to be plausible voltages.

Excessive voltage on the 12AX7 plates doesn't scare much of anybody, but idling a 1W tube at 2.9W might raise a few eyebrows. You might try restoring the high plate voltage on the reverb driver and then cooling the idle down by using a 470r cathode resistor instead of the original 68r resistor.

[g1]

That redrawn schematic is really bogus.

Thanks for doing the math, I knew something was fishy.
Nice job!
(for reference, the questionable redraw is here: https://music-electronics-forum.com/...1&d=1551704086)

[misterc57]

Thank you for the new schematics.

I am seeing this after having buttoned up the amp. The way I last left the amp was a 470R followed by a 56K for the dropping resistors in the supply.

I also brought the V5 12AX7 up to 368 VDC by using a 1.5K dropping resistor where the stock was a 220R. I previously used a 15K to drop the plate to 268.

This left me at

B+ 399
B++ 234
V5 plates 368

Some of these discussions get beyond my knowledge. I am always learning. The reason of cooling the idle down at V5 is something I need help to understand.

There are a few other things I notice that I would like to understand better.

V1 uses a 12AU7 and I read low plate voltages (around 38 VDC), if I place a 12AX7 the voltages go much higher. I know there is a difference in amplification factor, but did not realize it causes a change in plate voltage.

A 12AT7 is often seen as the reverb driver and phase inverter. Would I benefit to change from 12AX7?

The three inputs, look the same to me on the schematic. Yet I believe that I hear input 1 being louder and brighter, input 3 is more bass sounding and not as loud. Is this my imagination or is there a reason they have 3 different inputs on this amp.

Thank you. MarkO