Trace Elliot Speed Twin C50 Power Transformer Specs ?

[guitarspaz]

I have a Trace Elliot Speed Twin 50 watt combo that I "think" needs an output transformer. It's symptoms included somewhat reduced output for a while, then really bad sounding breaking bottle like distortion on real loud notes, then almost no output altogether Have to crank all controls wide open then you just barely head output)

I have done the following:

-Replaced all tubes and biased
-Checked all power supply voltages
-Replaced all High Voltage caps
-Checked coupling caps between amp stages
-Checked value of all pertinent power amp resistors.
-Verified that preamp runs fine by using the effects loop output into the poweramp of another amplifier.
-Tried a different speaker

A also performed some DC resistance measurements on the output transformer, which I know are of limited use, but they are:

Primary:
One end to center tap:37.5 ohms
Other end to center tap: 60 ohms
End to End:67 ohms

Shouldn't the overall equal the sum of the two parts ? Is this suspect ?

Output side:

Common to 16 ohm tap: 0.1 ohm
Common to 8 ohm tap: 0.6 ohms
Common to r ohm tap: 0.4 ohms

Does ANYONE know where I can get a spec to identify a replacement ? There are no markings on the transformer, and no part number listed in the service manual. Any assistance would be greatly appreciated.

[Enzo]

Did you try inputting a signal to the power amp in jack? (FX loop return)

Did you patch a cord from send to return on the FX loop?

Yes, the two sides of the OT primary should add up to the reading from end to end.

Disconnect the wires from the tube sockets and remeasure.

If you think the OT is bad, sub almost ANY other OT in there with clip wires. REmove the wires to the existing OT. DOn't worry about impedance or the NFB line, just clip the test OT primary to the tube sockets and B+. COnect the secondary directly to a speaker - don't conect it back to the amp output stuff. Does it work more or less? Or does it have the same issues? I keep an old Fender Bassman OT on the bench for this use.

I don't know the age of that model. Peavey is the current distributor of Trace in the USA, so if you are here also, contact their parts department and ask if that is a model supported. If not, ask if they know who has the parts for older models.

[guitarspaz]

Originally Posted by Enzo

Did you try inputting a signal to the power amp in jack? (FX loop return).

Did you patch a cord from send to return on the FX loop?

Yes, the two sides of the OT primary should add up to the reading from end to end.

Disconnect the wires from the tube sockets and remeasure.

If you think the OT is bad, sub almost ANY other OT in there with clip wires. REmove the wires to the existing OT. DOn't worry about impedance or the NFB line, just clip the test OT primary to the tube sockets and B+. COnect the secondary directly to a speaker - don't conect it back to the amp output stuff. Does it work more or less? Or does it have the same issues? I keep an old Fender Bassman OT on the bench for this use.

I don't know the age of that model. Peavey is the current distributor of Trace in the USA, so if you are here also, contact their parts department and ask if that is a model supported. If not, ask if they know who has the parts for older models.

Yes. I checked ths speaker by trying another, the poweramp by using a different preamp to drive it (didn't work), the preamp by having it drive another amp's power section (which worked fine), checked all of the voltages in the system for all of the tubes and the hand full of op amps on the effects loop, checked for coupling caps between stages for leakage, etc. Also did a full retube, replaced all of the high voltage electrolytics while I was in there, etc. Another possibility is that one of the op amps in the effects loop circuit between the effects in jack and the inverter/poweramp is bad, (because it is not truly bypassed even when not running effetcs. There's still a buffer amp in there on send and return) but there are no dead shorts I can say for sure. I don't have a scope or a signal generator to run it dowm more thoroughly. I would have tried replacing those op amps first (they are cheap), but when the DC resistance measurements were funny on the transformer, I was suspicious. I pulled the transformer off entirely and disconnected, and the measurements were the same (already had disconnected available plugs in the amp amyway). I'm wondering if I have bee getting a gradually more assymetrical signal over time due to some primary winding funnyness, and it finally let go.

Symtoms were: gradually reduced and worse tone output over a faiurly short period of time (a few weeks), then eventually really ugly breaking bottle like dustortion on real loud notes, and ultimately, no output other than a distorted whisper with everything wide open.

Trace guitar amps are/were supported by British Audio Service in Chicago. I emaield them, and got one back back saying the transformer was no longer available. Trace hasn't made "Guitar" amps in quite a few years. Peavey supports the bass line, but I haven't received responses form them yet.

I took a chance and ordered a 50 Watt Marshall JCM800 compatable transformer. I found a schematic for one on the net and it looked very similar (Resistor values and all) to my Amps schematic, so I'll keep my fingers crossed.

Thanks very much for taking the time to reply. I really appreciatre it. I'll update after I receive the new transformer and let you know how it goes.

[guitarspaz]

Fixed!!! It was the output transformer. Obsolete from Trace. I poked around and found an aftermarket unit designed for a Marshall 50Watt. I compared the Output circuits and values for the marshall to my Trace Elliot and they were nearly identical, so I ordered one and tried it. Bingo. It's physically a bit larger than my original, so I'll have to drill a hole or two, but I can deal with that. Thanks very much for your assistance.