WTF Happened? Traynor YSR-1 Custom Reverb

[tubethumper]

Hello Gents, I inherited an intact and working 1970 Traynor YSR-1 from my uncle more than 37 years ago.

Ive used it as a bass amp into a 2/12 cabinet for all of that time and its been dragged around the country.
Someone at a local music store told me to put ruby 6550s into it back in 1994. Thats 30+ yrs ago. Its played "warmly" ever since that happened, both tonally and physically. (yes I know it needs the EL34s)

Recently (2024-2025) if it was on for more than a couple hours it would start sounding mudded out and break up, and I would turn it off.
It was for the first time actually critically over heating and I would turn it off.
One night people were over, and being distracted I forgot to turn it off one night, although it was on standby.
the next day flipping it from standby to active and playing through it, it MELTED down and blew the magic smoke.

It looks like major overheating inside, with the wires melting off the speaker output jack, and the resistor there. also a red wire melting off of one of the filter caps. Brown resin cooked out of the output transformer and all over the chassis around the transformer.

What failed first to cause this cascade failure?, and what all do I need to do to save her in you opinions?

A good tech in a distant city looked at for me (as I was passing through) and said the power output transformer cooked, after the overheating. This is very obvious. He said she is salvagable, with a new power output and some soldering and new tubes.

My intention is to stitch her back together, doing the following:
1. Replace output transformer (I have new one in hand from hammond),
2. replace 2 filter caps 40um at 450v with JJ electronics black cans with chassis clamps,
3. replace the 2 ruby 6550 tubes with JJ electronics El34L's.

What else should I do while Ive got the soldering irons hot? someone said to replace the other caps on the board.

Thanks for your input! see photos

[tubethumper]

more photos. Thanks

[tubethumper]

more photos thanks

[Stevem]

I think your basic reason for the amp failure is just the normal age thing, but possibly and likely pushed along by running the 6550s without adjusting the bias voltage on them .

They would have needed a good amount more negative voltage then the original 6CA7 / EL34 tubes would .

This is also why over time the amp started to worse and worse as you used it, not to mention the original filter cans going south more and more.

[didit]

My intention is to stitch her back together, doing the following:
1. Replace output transformer (I have new one in hand from hammond),
2. replace 2 filter caps 40um at 450v with JJ electronics black cans with chassis clamps,
3. replace the 2 ruby 6550 tubes with JJ electronics El34L's.

What else should I do while Ive got the soldering irons hot? someone said to replace the other caps on the board.

Electrolytic capacitors don't age well. Remarkable it's survived to 2026. Along with those two bulk power capacitors there are five more inside the chassis -- they all have shiny blue plastic sleeves over an aluminum body. Those should all be replaced regardless. The bias filter in particular is key to survival so I've started occasionally replacing these with film capacitors of roughly equal values.

0/Get the schematic and trace it against your amp. This will help understanding better what you're about to perform surgery on.
1/ No reason to assume that output transformer survived but you can confirm with testing. Having been evidently overheated it's wise to replace it regardless.
2/ Recommend some F&T 500V 50+50uF vs the JJ's you've tagged; since with a nominal 320VAC on the secondary of your power transformer 450VDC is easily exceeded.
3/ somewhat a matter of taste but EH 6CA7s would be my choice, or perhaps current production KT77s.
4/ install a variable bias control and read up on the procedures to using it during bring up phase.

Realize that you may have other components that have drifted off spec or been damaged during this catastrophe. Do you have a basic multimeter along with a decent soldering iron? Get a guide to bringing up an amp after building and/or repairs, and follow it cautiously and completely. Pause after the first few steps and confirm readings with another post to this thread and people will pitch in to assist.

Best ..

[tubethumper]

Thanks for the recommendations, looks like I ended up with the DD EL34L tubes in my order already on the way, but I had thought to try the 6CA7, maybe ill buy a spare set and change out to check tonal differences.
good rec on the F&T 500V 50+50uFs.

yes, im decent with poking around with a multimeter and have a collection of soldering irons from 5watt to 500 watt (huge).

two questions:
1. good replacement brand and type for board capacitors, and the bias capacitor?
2. can anyone point a direction to installation and use of a variable bias control?

Thanks a ton. all the best

[/quote]

Electrolytic capacitors don't age well. Remarkable it's survived to 2026. Along with those two bulk power capacitors there are five more inside the chassis -- they all have shiny blue plastic sleeves over an aluminum body. Those should all be replaced regardless. The bias filter in particular is key to survival so I've started occasionally replacing these with film capacitors of roughly equal values.

0/Get the schematic and trace it against your amp. This will help understanding better what you're about to perform surgery on.
1/ No reason to assume that output transformer survived but you can confirm with testing. Having been evidently overheated it's wise to replace it regardless.
2/ Recommend some F&T 500V 50+50uF vs the JJ's you've tagged; since with a nominal 320VAC on the secondary of your power transformer 450VDC is easily exceeded.
3/ somewhat a matter of taste but EH 6CA7s would be my choice, or perhaps current production KT77s.
4/ install a variable bias control and read up on the procedures to using it during bring up phase.

Realize that you may have other components that have drifted off spec or been damaged during this catastrophe. Do you have a basic multimeter along with a decent soldering iron? Get a guide to bringing up an amp after building and/or repairs, and follow it cautiously and completely. Pause after the first few steps and confirm readings with another post to this thread and people will pitch in to assist.

Best ..
[/quote]

[sluckey]

2. can anyone point a direction to installation and use of a variable bias control?

Adding a bias pot will be easy in that circuit. However, be patient. I urge you to fix what's broken before even thinking about a mod.

[TUBEDUDE]

It's amazing how many components will sacrifice themselves to save.a.fuse.

[tubethumper]

yeh and the fuse is a little undersized to boot, tiny little filament in there. surpassed the windings of the transformer. Makes no sense, other that chinese rating system on the fuse perhaps.

[tubethumper]

can you tell me where you suggest a bias pot would be best installed in that schematic?

2. can anyone point a direction to installation and use of a variable bias control?

Adding a bias pot will be easy in that circuit. However, be patient. I urge you to fix what's broken before even thinking about a mod.

[tubethumper]

q

[didit]

can you tell me where you suggest a bias pot would be best installed in that schematic?

Simple easy, as Steve noted.

If it was mine I'd do the following while the iron is hot replacing the pair of capacitors that provide bias filtering. And, using that schematic's component numbering, R47 (?) original 47K replaced with 39K and R48 is replaced by a 15K linear trimmer in series above a 25K resistor. The trimmer should be wired as a variable resistor with wiper tied above, which is safe even if the wiper connection fails.

This set of values preserves overall series resistance of ~88K and presumably puts upper range of negative voltage at a sane safe level. Depending on the actual line AC this provides ~18V of adjustment, from about -30 down. Different values could work -- .e.g, a 25K trimmer and 15K fixed should work,but doubtful that range of adjustment is necessarily helpful. Use good metal films and a quality trimmer.

Unclear if this amp came with Traynor's easy access chassis lid. If it doesn't, and you want ready external access, a through chassis 25K pot works but requires drilling etc. Recommend you also put a pair of one Ohm 1% metal films on the power tube cathode connections to ground to make your measurement easier.

Others may have other suggestions.

Best ..

[tubethumper]

thanks for this instruction, Im digesting all this.

can you tell me where you suggest a bias pot would be best installed in that schematic?

Simple easy, as Steve noted.

If it was mine I'd do the following while the iron is hot replacing the pair of capacitors that provide bias filtering. And, using that schematic's component numbering, R47 (?) original 47K replaced with 39K and R48 is replaced by a 15K linear trimmer in series above a 25K resistor. The trimmer should be wired as a variable resistor with wiper tied above, which is safe even if the wiper connection fails.

This set of values preserves overall series resistance of ~88K and presumably puts upper range of negative voltage at a sane safe level. Depending on the actual line AC this provides ~18V of adjustment, from about -30 down. Different values could work -- .e.g, a 25K trimmer and 15K fixed should work,but doubtful that range of adjustment is necessarily helpful. Use good metal films and a quality trimmer.

Unclear if this amp came with Traynor's easy access chassis lid. If it doesn't, and you want ready external access, a through chassis 25K pot works but requires drilling etc. Recommend you also put a pair of one Ohm 1% metal films on the power tube cathode connections to ground to make your measurement easier.

Others may have other suggestions.

Best ..