Traynor YGM-3 design issues?

[Iplayloud]

I don't think these still need introduction, you can't live in Canada without stumbling into old Traynor amps left and right. Pawn shops, etc..

The YGM-3 model was always seen as an incredible value, literally a ptp Deluxe Reverb for half the price but... nobody seems to care/notice that they're totally missing the 3rd gain stage after the reverb recovery?

When looking at the schematic you can see the plate resistors in the preamp have very high values. I assume trying to sqeeze out more volume/gain from the preamp, to compensate for that missing stage. (BTW they crearly don't have the power and volume of a DR) I'm thinking, should they not have reduced the 3.3M/10pf combo instead? My understanding of this "brick-wall" was to prevent Fender amps from distorting like a Marshall. Is it possible that this huge resistor may not have it's place if the 3rd gain stage is missing?

I'm trying 150k plate resistors in the preamp now, and the amp lost alot of volume. I want to raise the preamp plate voltages to hopefully regain the fullness and musicality lost by starving the preamp. I'm considering ditching the vibrato to wire the lost 3rd stage.

Before I sack the vibrato, should I try a lower value for the (R8) 3.3M? Maybe 220k like the normal channel of AB763 circuit that also have only 2 stage?

Schematic:
https://music-electronics-forum.com/attachment.php?attachmentid=51588&d=1545229903

[Leo_Gnardo]

Part of the reason for that huge 3M3 mix resistor is to try & prevent a feedback situation from setting up between the reverb return & the stage driving the mix node. You could try sliding down a couple notches, try 2M2 or 1M resistors. As long as it doesn't start to howl, whistle or moo, you're OK.

How are the cathode bypass caps in your pre stages? Sometimes they quit working with age. A fast way to tell is simply clip in another similar size cap parallel to the existing one. If the gain perks up then cut out the old one & swap in new.

A friend of mine had one of these amps - long ago modded to use 6L6 instead of EL84. He also wasn't too thrilled with it. He mentioned he owned a tweed 4x10 Bassman way back when they were new. "Best amp I ever had!" Until it got stolen, all the way back in 1962 (!) With that in mind I changed the EQ in his Traynor to the 5F6A style and he got way happier with it. A bit of work but it may help.

Also, I've never encountered a stock 60's-70's Traynor that had decent speaker(s) so you may want to consider that. If yours is still the stock speaker most anything else would be an improvement.

[Iplayloud]

Great info, thx! It's been recapped already. Speaker swapped too. Seems like alot of people have owned one but then passed it along. I think they're very close to being a great amp. If not for the resale value I'd totally be ripping that vibrato and wire that 3rd gain stage. I'll see in the next couple months if it's a keeper and decide about that.

Do you think the huge plate resistors are there to sqeeze more gain/volume? Like the 470k plate resistor of the reverb recovery. Who in their sane mind would swap for such a value? It drops the plate volt from 180v in a Fender to 70v. Gee might as well put a transistor there haha.

It's weird because it's so not in-line with Peter Traynor's mentality, like the YBA-1a built like a 50w plexi but with huge xformers, a case fan, and marketed as a 90w monster. Then you make a DR clone and paralyze it by removing a gain stage. Oh well..

[uneumann]

Great info, thx! It's been recapped already. Speaker swapped too. Seems like alot of people have owned one but then passed it along. I think they're very close to being a great amp. If not for the resale value I'd totally be ripping that vibrato and wire that 3rd gain stage. I'll see in the next couple months if it's a keeper and decide about that.

Do you think the huge plate resistors are there to sqeeze more gain/volume? Like the 470k plate resistor of the reverb recovery. Who in their sane mind would swap for such a value? It drops the plate volt from 180v in a Fender to 70v. Gee might as well put a transistor there haha.

It's weird because it's so not in-line with Peter Traynor's mentality, like the YBA-1a built like a 50w plexi but with huge xformers, a case fan, and marketed as a 90w monster. Then you make a DR clone and paralyze it by removing a gain stage. Oh well..

Before you kill the reverb - you might just put a LND150 gain stage where the fender has it. Then you can set all the resistors to where you want them and keep the reverb too.

[Leo_Gnardo]

Great info, thx! It's been recapped already. Speaker swapped too. Seems like alot of people have owned one but then passed it along. I think they're very close to being a great amp. If not for the resale value I'd totally be ripping that vibrato and wire that 3rd gain stage. I'll see in the next couple months if it's a keeper and decide about that.

Do you think the huge plate resistors are there to sqeeze more gain/volume? Like the 470k plate resistor of the reverb recovery. Who in their sane mind would swap for such a value? It drops the plate volt from 180v in a Fender to 70v. Gee might as well put a transistor there haha.

It's weird because it's so not in-line with Peter Traynor's mentality, like the YBA-1a built like a 50w plexi but with huge xformers, a case fan, and marketed as a 90w monster. Then you make a DR clone and paralyze it by removing a gain stage. Oh well..

That friend of mine was strictly a jazz player - never needed to go into the crunch zone so he didn't care how far up he had to dial the volume control, as long as the noise level was low and he could get a good clean sound that worked with his D'Angelico.

I s'pose you could grab a pinch of gain back by increasing preamp plate resistors. It's not much but it might get you into the place you want.

YBA-1a funny that was my first bass amp. Served me well through the 70's. Two improvements : when I swapped out the cheezy stock 15" speakers with half-dollar size magnets for a couple of ElectroVoice EVM, wow what a huge improvement that was. Then the improvement I didn't know enough to make back then. Bridging two of the terminals on the "Low extension" (really midrange) pot would have allowed me to cut wooly low mids and get the sort of tone I was getting from a borrowed 100W Fender bassman head with the mid turned all the way down. It was a good tough amp that saw me through thousands of gigs. YBA-1 in all versions still is a sleeper when it comes to price with respect to quality. Smart people grab 'em cheap and put 'em to work after some maintenance and perhaps a few minor mods.

As far as the reverb recovery plate resistor and its effect on gain, if you have enough volume on the reverb who cares how far you have to dial up the pot. I know most Fenders it's too much if you go past 3, or on some even 2. My view is so what if your Traynor's sweet spot is at 7 or 8 or 9? As long as it sounds good, don't sweat it.

If the Guitar-mate still doesn't holler enough to satisfy, accept it for what it is, a clean-mostly amp, and put your choice of overdrive/boost/fuzz box between your guitar and its input jack.

[Iplayloud]

Before you kill the reverb - you might just put a LND150 gain stage where the fender has it. Then you can set all the resistors to where you want them and keep the reverb too.

Oh I'm not seriously considering putting a transistor there. I just meant, might as well because with a plate voltage that low, that reverb is going to sound cold. (Mainly comparing the circuit with the AB763 Fender Deluxe Reverb)

[uneumann]

Oh I'm not seriously considering putting a transistor there. I just meant, might as well because with a plate voltage that low, that reverb is going to sound cold. (Mainly comparing the circuit with the AB763 Fender Deluxe Reverb)

I know it's sacrilegious - but I am serious.
If you just need gain, a mosfet stage can be totally-transparent tone-wise, and by using it you can make all the tube stages work and sound the way you want them to. Can't see a downside for $2 investment. No holes drilled so it's easy to remove if you need to restore the amp as "vintage".

[Chuck H]

Just so's everyone is on the same page and tracking.

[Leo_Gnardo]

Just so's everyone is on the same page and tracking.

Thanks for the schemo Chuck. I looked it up on Prowess but had to turn my head sideways to read it. And, upon examination, AHA! If the reverb's sounding on the weak side, you can boost it by adding a bypass cap say anywhere from 1 to 25 uF across the recovery triode's cathode resistor.

[uneumann]

Just so's everyone is on the same page and tracking.

Thanks - looking at it now, another option is to re-purpose the trem osc triode for your gain stage and use an LND150 for the osc.
That keeps the signal path "pure". Just something to consider.

[Iplayloud]

If we go back to the elephant in the room with this amp, being the completely missing 3rd gain stage (versus a Deluxe Reverb). How terrible was that idea on a scale of 1 to 10? You build a huge plywood box, all PTP, big Hammond transformers, clone a famous circuit, then at 99% of the way, sabotage it... probably just to save .. how much did a 12ax7 cost in 1973? Why not rewire this and make a real useable/giggable DR !!

[Helmholtz]

Input to reverb driver tube(s) is drawn wrong in the schematic: 560p coupling cap should connect to the grids (not plates).

[Chuck H]

Yes. I noticed that too while I was constructing the simulation. I just hadn't gotten back to post about it before you did. Obvious typo.

[Chuck H]

Ok... Looking over the schematic there are a couple of simple things that could be done to raise the gain quite a bit.

Look at the NFB loop. It's basically hardwired like a presence control on ten. You don't need that with el84's. They're better off with no NFB at all in this case, JMHO. So disconnect the NFB loop. Along with that there are a couple of other changes to the PI circuit. Change the 470k PI grid loads to 1M. Change the 6.8k PI tail to 10k (this doesn't raise gain but it does improve balance). And change the 4.7k to a jumper (zero ohms).

Change that 3.3M resistor to 2.2M. Like Leo said, if the reverb seems too weak to balance well with the dry signal you can add a bypass cap to the recovery stage.

Change the 100k power tube grid loads to 220k.

Because there will be a little more drive to the power tube grids it's probably a good idea to add 470R screen grid resistors. I know 1k is the usual value here but you're not going to be driving the tubes all THAT hard and 470R sounds better (to me).

That's it. I'm guessing that your amp as it is doesn't start to break up until seven or even eight on the volume knob? These changes should have it starting to clip around six. Whereas a DR starts clipping around four or five.

Below is the spice examples of drive at the power tube grids for the stock amp and then with the modifications for more drive and better balance.

[g1]

I don't want to get too far into it, but the idea that Pete built this as a 'DR clone' is ridiculous and somewhat offensive.
It's one of the most popular vintage Traynor amps bone stock. If you don't like it, go ahead and mod away. But please don't imply design flaws.