1970 Traynor YGM-3 O/T problem?

[galaxiex]

Hello all.
New poster, long time lurker.

Sorry if this is a bit long...

I'm working on a 1970 YGM-3 that seems to have an O/T problem.
When I got this amp it had been extensively modified with triode/pentode switch,
hole drilled in the back for a master volume, Fenderish TMB tone stack with the mid control in the 3rd input jack hole.
Oh, and a hole punched in the chassis for an extra 12AX7 preamp tube.

It also showed evidence of a fire at one time with a big burn/scorch mark above one of the EL-84 sockets. V3
Must have been bad cuz the socket had been replaced and some wiring, and the other wires nearby look a bit toasty too.

I replaced the cheap fiber socket with a good phenolic type.
The other socket looks fine.

So I rewired it as much back to original as I could, with stock parts values, pots etc, from the schematic.
Removed the extra 12AX7.
Added adjustable bias and 1ohm cathode resistors.
Added 2.2K screen resistors.
Replaced all electros with new, including the cans.

B+ ~ 435V

Got it up and running but with the bias set to -15.5V per the schem and measured ~50ma at the 1ohm cathode resistors,
it red plates the output tubes, but sounds awesome.

Adjust bias closer to -20V which gives ~30ma at the 1ohm cathode resistors.
Sounds like crap with crossover distortion. No more red plate tho.

It does have a tiny hum, never notice it when playing.

Tinkered with it for some time and went to take a voltage reading at the plate of V3
and as soon as I touched the Fluke 110 voltmeter + lead clip to pin 7
There was a tiny spark and the hum went away and there was noticeable background hiss.

It does not do this if I hook up to V4 pin 7.

V3 plate 395V
V4 plate 405V

Disconnected the O/T primary leads and took R readings.

V3 side to C/T 119.3 ohm
V4 side to C/T 163.6 ohm

Is my O/T done?

TIA

[g1]

Have you tried other power tubes? Although the 2 sides of the OT primary seem a bit far apart, I think any fault in the OT would give you other symptoms as well. Seems more likely a bad power tube was giving the hum and you 'scared' it into cooperating.
As far as the bad sound and crossover with a more conservative bias, I'd be interested to see how that is affected by going to 1K screen R's, rather than the 2K2's you have in there now.

[galaxiex]

Thanks g1,

This was with new JJ EL-84's matched pair 12hr burn in 32ma from Tube Depot.

A bit more testing... or I should say... poking at it with a stick...

I powered up this morning and put the meter probe on pin 7 V3.
Nothing seemed wrong.
On a hunch turned the vol control up,
and at 3/4 volume and up, the hum goes away, and got kinda loud hiss from the speaker.

Repeated the same test on V4 and no change in hum, no hiss.

Interesting that it does this ONLY when the meter probe is on the pin 7 V3, and not when I probe pin 7 V4.

Paying a bit more attention now, I noticed the hum is actually from the PT and the fact it goes away kinda worries me.

I think something is shorting somewhere, but why only when I probe that pin 7 V3?

Also, with no probing any pins, turning up the vol at 3/4 there is a "glitch" sound from the speaker.
Sorry, can't describe it any better than that.

[g1]

Could be oscillating I suppose.
Try swapping the power tubes around and see if the issue remains at the V3 socket or follows the tube.

[galaxiex]

My mistake, the tubes were Mullard EL-84's.

Anyway, I swapped the tubes around and no change.
I do have a pair of JJ's so tried those and still no change.

I pulled the Tx and got strange resistance readings on the primary if I tap on the Tx the reading changes.
Going from end to end it reads ~278 ohms but tapping on the Tx causes the reading jump higher.
I saw it go as high as 400 ohms but only once.
Consistently jumps up to ~ 310 ohms.

I've ordered a Hammond replacement 1750S Tx.

[galaxiex]

Got the new TX installed and the amp sounds much happier now.
No more strange noises.

The new Tx is somewhat smaller than the original... seems to work just fine.
Did not have to drill any new holes. The original holes are slotted and the new Tx just bolted in.

Maybe I'll get the original rewound...

[galaxiex]

So I've been tinkering with this amp...
I don't feel bad about it cuz the poor thing was heavily modded when I got it. (first post details previous mods)

Decided to do almost a complete re-wire, esp the pre-amp, reverb, and tone stack.

Here's a schem of what I did...



Surprisingly... or not... this is almost exactly like the Blues Junior conversion I did in this thread....

http://music-electronics-forum.com/s...158#post501158

Doesn't sound the same tho...

[g1]

Just as long as another Traynor doesn't get marshallized. People get their citizenship revoked for that.
Up here Traynorizing a marshall is ok though.

[galaxiex]

So after all the monkey business this amp has gone thru...

There is quite a bit of ugly flux all over the board.
I know that flux can become conductive, but so far nothing bad seems to be happening.
No-one's gonna see it, but I'd like to clean it up some.

Should I bother?
If so, how would you do it?

I was thinking some isopropyl alcohol and an old tooth brush.
I have access to compressed air as well.

[The Dude]

I'm not sure I'd be concerned about the flux. That said, I'm sometimes a bit anal about that sort of thing, myself. I just scrape it off with a little screwdriver and blow the rest with compressed air or a toothbrush (if you're so inclined).

[galaxiex]

Thanks, I'll try scraping/blowing first. See how it goes...

[galaxiex]

Bumping my own thread as I dug this amp out and have been playing it, and something I never noticed before...

I had never turned the reverb up full before,

and now when I do that, the amp makes some very distorted reverb noises.

So digging into it I scoped the reverb and got a nasty looking wave form.

Turns out the reverb TX was out of phase...

With that out of the way, at 10 the reverb still sounds quite distorted, just not as nasty as before.

So I tinkered with some values and got it better, but would like some more experienced eyes on this.

Here's the updated schematic as the amp is now.
Please compare to the schem in post #7.



Changes:

Reverb pot arrangement, wiper now goes to C14

Added C27

R29 changed to 1meg.

I basically copied the Princeton Reverb B1270 schematic reverb section.

Anyone see anything that doesn't look right?

Thanks!

[Helmholtz]

Turns out the reverb TX was out of phase...

I don't think that reverb transformer phase really matters as the tank acts as a multiple delay line after which specific phase relations of frequencies to the original signal are lost. But if it sounds better with reversed phase - fine.

[galaxiex]

I don't think that reverb transformer phase really matters as the tank acts as a multiple delay line after which specific phase relations of frequencies to the original signal are lost. But if it sounds better with reversed phase - fine.

Thanks,

When I say "out of phase" I mean the primary and secondary with respect to each other.

I don't know if it matters, but I switched the primary leads and left the secondary alone.

The nasty, raspy, buzzing noise with the reverb control at 10, got way less, and the waveform on the scope looked better.

Edit;

Here's the spec sheet for the TX.

I swapped the blue and red wires.

40-18034.pdf40-18034.pdf

[Helmholtz]

but I switched the primary leads and left the secondary alone.

I swapped the blue and red wires.

Yes, that's what I meant with reversing reverb driver phase.