Traynor YGM-3 Add Adjustable Bias

[Steely]

I recently came across a '77 Traynor YGM-3, and have been happily tinkering away...

It had a blown 6BQ5 power tube, so I have replaced with a new matched set (EL84 EH) - but they run extremely hot (glowing plates!)

I'd like to change the fixed value bias to adjustable, but need some assistance...

The schematic for this model is here:

http://www.informatik.uni-bremen.de/...mate_ygm3a.pdf

I know I have to replace the fixed resistor with a pot, in series with a smaller resistor (to protect from a direct short to ground), but I'm not certain which resistor. I have it narrowed down to either R38 (15K) or R39 (22K).

Is there anyone out there who can tell me which resistor to replace, and recommend a pot value?

Any advice would be greatly appreciated.

George

[sportster4eva]

Yup, it's R39 or/and R44 you would change to increase or decrease bias voltage.
There's a couple of ways you could do it.
You could place a 15-25k pot between R39 and ground, With the wiper connected to the CCW terminal, and the CCW terminal connected to ground, and the CW terminal connected to R39. Turning the pot clockwise(CW) would then shunt the resistance of the pot, reducing the bias voltage, raising the output tube's current.

Another way would be a 100k 2w resistor and a 50k 2w pot with the wiper connected to the CCW terminal. that end would go towards R44 or diode, depending on which way you pick to wire it. (diode/resistor/pot - or - diode/pot/resistor, it doesn't really matter) the CW terminal would connect to the wire or trace that goes to the power tube grids, or to R44 if that's the way you picked. Wired this way, as you turn the pot clockwise, the negative bias voltage would drop, and the tubes would draw more current.

I like the first method, since it's on the ground side of the bias circuit, and if the resistor or pot ever fails, it will drive the tubes toward cutoff, instead of red plating them.

However----- this amp uses a bias varying tremolo, and there's a possibility that if C27 is leaky/bad it could be sending voltage to the grids, screwing up the bias point, even more so when the intensity is set high. That needs to be ruled out.

Guys, if I missed anything, chime in.

Hope this helps, and please be careful inside there.
Paul

[Steely]

Thank you, Paul.

I think I'll pick up a few different pots and resistors, and try various methods.

It had already dawned on me, that there probably wasn't just one solution, as there are several resistors that effect the bias voltage. But, as you point out, there is probably one "Better" or "safer" method.

Thanks for the tip on C27 - I hadn't really considered the impact of the tremolo circuit.

Thanks again!

George

[Mr. Droopy-Drawers]

Don't Touch R44!

I mean it! Take out R39 and replace it with a 10K pot. Wire up the ends of R38 and C29 to the first terminal, and add an 18K resistor (for now) between the third terminal and ground (the back of the bias pot is fine). The middle terminal (wiper) of the bias pot goes to the third terminal of the Tremolo 'Intensity' pot. You can get a 'reissue' CTS bias pot from people like Mojo or AES.
What's strange is that many of the YGM-3's I picked up had a bad output tube! They must have come right from the factory with a bias voltage way too low. Or else Philips 6BQ5's were built like a brick outhouse compared to Russian junk these days.

[Rob Mercure]

MDD,

Do you mean "whore to culture?" This was one of Dick Peak's - former Chair of the English Department at Clinch Valley College many years ago - favorite jokes about 30 years ago!

Rob

[Steely]

Mr. Drawers,

I have replaced R39 with a 10K resistor and a 25K, 20-turn trim pot. Works like a dream.

While adjusting the tube bias, I've discovered that my "matched" Electro Harmonix EL84 tubes, purchased recently on-line, are not even close to a match. Using the cathode resistor method to measure and calculate static dissipation wattage, one tube was at 12.1 watts (and starting to red-plate), while the other was 8.4.

I tried another set, Sovteks, and they were a much better match (11.3 and 11.9)

I had read, somewhere, that Traynors have higher than normal plate voltage - mine is running about 400V. Since the spec for EL84s is 300V, this may be responsible for the tube failures you've come across.

Since you seem well versed in Traynor amps, I have a quick question for you...

My amp has a 16 ohm Celestion G-12M. Is this the stock speaker, from '77 (The speaker itself dates to '76), or was it added sometime in the last 30 years? Also, would I see any benefit from changing to an 8 ohm speaker?

Thanks for all the info that you, and everyone contributes to this forum. I'm learning loads of great info!!!

George

And since your into puns...

"If you're not part of the solution... Your part of the precipitate!"

[Hyperborea]

My amp has a 16 ohm Celestion G-12M. Is this the stock speaker, from '77 (The speaker itself dates to '76), or was it added sometime in the last 30 years? Also, would I see any benefit from changing to an 8 ohm speaker?

That is not the original speaker. The YGM-3, and from what I understand most of the original Traynor amps, had Marsland or CTS speakers (both Canadian brands). It was also an 8 ohm speaker.

I came across this post and joined the forum as I was searching out info on the YGM-3. I have recently bought one and need to replace my electrolytic caps (ordered and waiting on them).

[Regis]

That is not the original speaker. The YGM-3, and from what I understand most of the original Traynor amps, had Marsland or CTS speakers (both Canadian brands). It was also an 8 ohm speaker.

I came across this post and joined the forum as I was searching out info on the YGM-3. I have recently bought one and need to replace my electrolytic caps (ordered and waiting on them).

I have a YGM3A and the Marsland was indeed the speaker that came with it originally. Sounded like ass, I replaced it with an Eminence Private Jack.

[Enzo]

CTS (Chicago Telephone Supply) is a Canadian brand?

[AL30]

I have a YGM3A and the Marsland was indeed the speaker that came with it originally. Sounded like ass, I replaced it with an Eminence Private Jack.

Gotta agree with that. I replaced mine with a Celestion G12H30 - HUGE improvement. I'm running JJ EL84's and have had no problems. I also wired an adjustable bias but it's been a while and I can't remember exactly what I did. I think this is a really nice sounding amp. Lot of amp for a little $$$.

AL

[Hyperborea]

CTS (Chicago Telephone Supply) is a Canadian brand?

Whoops. I wasn't sure but I thought it was and that the 'C' in the initials stood for Canada or Canadian. Thanks for the correction.

I don't know the board etiquette on related questions in a thread so I'll ask here and move it if I should later.

Screen resistors: I see a number of discussions on the web about adding / upgrading the screen resistors on the Traynor amps. On the YGM-3 that would be R40 (470 ohm / 2W) shared for both the output tubes, right? What should it be changed to? I also see reference to that single resistor being replaced with one on the pins of each tube socket but in the current standard circuit it's not. Why do this?

I'm doing a full electrolytic re-cap of my YGM-3 is there anything else that I should be doing for durability / reliability at the same time other than the adjustable bias (I'm going to do that)? Not worried about tone mods or such until I get mine back up and running right to try it out for a while first. I'm pretty much a newbie with tube circuits though I do understand the theory and I have done a fair bit of low power analog and digital circuit work.

Thanks.

[Mr. Droopy-Drawers]

You almost WISH that was an RSC speaker!

The original was a Marsland. They aren't bad per se, but very inefficient. Just a boring side story; a few friends of mine gathered with some pizza, beer, and our Super Reverbs. Just having some fun comparing them. We even invited along a bass player and drummer. We had four samples, and one was a very clean '65 that was purchased without any speakers. My friend had an old Traynor 4x10" cabinet laying about, so the Marsland speakers went inside the Super Reverb. My 'almost' stock '67 just absolutely buried the '65 with Marsland speakers. Switching chassis/speaker arangements, the conclusion was the Marsland just didn't have the sensitivity of the Jensen speakers. Other guys had Naylor/Eminence or CTS, and the volume difference was unreal. In the end, he had the last laugh, as he could 'dime' his Super Reverb, and get a great tone at a managable stage level. There's no point here other than sometimes those inefficient speakers save stage problems.
Those other speakers from Canada? RSC, which stood for Radio Speakers of Canada, and were assembled up here in Canada with Jensen parts. Having a vintage RSC is exactly the same as having a vintage Jensen.
My YGM-3 has an Eminence Legend in there now, but a Red Fang just sounds like God. Using a 16-ohm Celestion will cause an impedance mismatch, and you'll lose some power.

[trood]

YGL-3 Mk3

Sounds like you guys know your stuff, My Mk3 has decided to cut the sound out as I increase my tremelo intensity going completely silent @ 10. It is the opto version not the variable bias. I have check for shorted caps and/or bad solder broken wires etc. The one thing I see is pin 8 of V3 is supposed to have 35V but is actually 10V. I replaced the tube with no luck. Reverb works fine.

[Animatic]

Hello y'all
I joined because I saw this thread. I bumped into a YGM-3 last week and threw some cash down to hold it till tomorrow. I pretty sure it's 74-75, decent condition, trem/verb sound fine, and just some noisy pots. It has a Celestion in it now.

6QB5s might need changing. But I'll play it in a bit first. It's a bit hard to find NOS 6QB5 here, but there are a few floating around Bangkok. I have matched sets of TAD and JJ El84's but don't want to risk them to red plating quite yet.

I attribute much of the imperfection during the test to the crapola Tele clone I had to try it through.

I've seen some good mod ideas on Ytube and this bias thread is useful of course. 1st coupling cap likely to go to a .01 rather than 0.1, will check out taking out the presence cap, and adding 100pf fizzy cap. And eventually a PPIV. Posasibly a mid pot to at some point.

But I suspect I just got a sleeper amp that appeared on an island out of the blue. The clips of both mod'd and stock amps sound like a sound I can be very happy with this baby in the studio's collection.

I've built a 50w Dumble clone w/Celestion 12" tone ring cab, and/or 15" tone ring cab,
A 5F6a w/4-10 Webers, that very much pleased Charlie Musslewhite last winter.

And an SE amp 1st tube a Vox'd 12ax7, feeding Marshal'ish tone stack, into mostly Dumble 12AX7 overdrive 2nd tube, to an EL84 and 6V6 each with MV, into 25OT and 2-10" Mojos. Great sounding little amp that holds up well next to the 5F6a for live volume.
I have an 18 Marshal partly assembled, but this Traynor will be a great addition, and likely a fine match for the 18w live. I agree these amps are a great value and under rated in general.

[akimball442]

You will love it- especially if you love modding amps.

I removed the feedback loop and the 'presence' resistor altogether on mine. Wakes it right up. I'm running a massive EVM-12 speaker.

Changing the first cap to a lower value is an absolute must. .01 or even 500pf is good.

I added a 12ax7 to mine and installed a 5F6-A tone stack- as I did not care for the stock tone stack. It's very 'hifi' which I don't like in a guitar amp.. it's a personal preference thing for sure.

A vox tone stack is pretty tasty in this amp too.... It responds better than any amp I've ever had as a test-bed for mods. And with a good speaker it gets impressively loud- loud enough to gig with, and it's very well built and extremely reliable. I've never had any tube failures, even with the high B+.