Trace Elliot Trident

[Dmoney]

Here is one some people might want to see.
A friend brought this round last night for me to fix it. hes had it in storage for 4 years. The current power valves are marshall branded EL34's installed 7 years ago. He's owned the amp 10years. All the preamp valves are 7025's and I think they might be trace elliot branded.

Its a weird amp. Clean channel 1, Channel 2 is like a JCM800 with an extra EL84 pentode stage after the tone stack????, channel 3 is SLO lead.

It wasn't making any noise.
So first thing I found was a blown mains fuse. Secondly... a totally missing screen grid resistor (red circle), and some heater wiring missing its push on connector soldered directly to some pins (blue circle)
When he dropped it off i noticed it was in 'triode' mode. he said it blew a valve and he got the marshall valves installed... looks to me like whoever did that chopped out a screen resistor and flicked the amp into triode mode, hoping it would never see pentode mode again. weird.

It does make noise but it sounds pretty poor. The power stage is probably a bit worse for wear, and the preamp is a bit screwed. Channel 2 seems pretty dull and borderline microphonic. channel 3 squeals/whistles if you use the boost switch on it.

Probably needs a good overhaul in the valve department as well as a new 1K/5watt resistor. The footswitch also seems a bit off, maybe its not, but worth checking.

thought id stick this up to demonstrate a "quality" repair job from the past!

[Frank]

Certainly it looks like someone's had a good old poke around in there without the faintest idea of what he was doing. Maybe he ran out of spare resistors. It's certainly a sloppy repair job, I'd guess someone was pressed for time or just couldn't be bothered doing a proper job on a cramped PCB.

Not sure about the EL84, is it a reverb driver by any chance? Like you say, a new set of tubes and replaced components should make a huge improvement but I'm always wary of amps that blow fuses. Proceed with caution.

EDIT: schematic shows a 12AX7 as reverb driver and the EL84 as a straightforward volage amp right after the EQ, very unusual.

[HTH AMPS]

EL84 as a reverb driver was my first thought too - VHT used to do this and I'm sure they changed away from it after having problems with it.

I see its a Paul Stevens-designed amp - that guy knows his onions, sound bloke.

[jpfamps]

The EL84 seems to be there simply tp give some pentode tone to the pre-amp.

The reverb driver is a Darlington pair driven from the plate of a ECC83. This is a cheaper method than using a transformer.

This era of Trace amps (and the Trace-made Gibson amps) have a poor reputation for reliability, with the OTs and the switching being the main problem areas. However, many people like how they sound.

[Dmoney]

It probably sounds ok to most. Channel 3 is an almost exact copy of the SLO100 lead channel. So that ain't going far wrong. The head doesn't have the reverb circuit either.

Turns out that this thing was running stuck in triode mode, with both valves on one side of the OT primary in a failed state.

[HTH AMPS]

The EL84 seems to be there simply tp give some pentode tone to the pre-amp.

The reverb driver is a Darlington pair driven from the plate of a ECC83. This is a cheaper method than using a transformer.

This era of Trace amps (and the Trace-made Gibson amps) have a poor reputation for reliability, with the OTs and the switching being the main problem areas. However, many people like how they sound.

good spot, I just cast a quick eye over it and assumed the EL84 was the reverb driver.

that a cool little trick, will have to try that out - curious to hear how it sounds.

[jpfamps]

I've seen an EL84 used in a bass pre-amp (can't remember which) as a little single ended amp.

The Garnet Hertzog also use a small SE amp with a dummy load as a "distortion pedal".

[Dmoney]

this amp now works in pentode mode!
horribly delicate board traces on this thing. also, the connectors used to jump signal or voltage around have actually been glued into place by some idiot. This is probably why one connector is missing from 6.3vac line.

it still doesn't sound right. using the boost switch on channel 3 makes it squeal at any volume. I have a bunch of spare sovtek and JJ ecc83s, and even with those in it still does it. channel 2 sounds terrible, but im guessing the EL84 might be shot and I don't have a spare. . Clean is seems to be ok.

[HTH AMPS]

I've seen an EL84 used in a bass pre-amp (can't remember which) as a little single ended amp.

The Garnet Hertzog also use a small SE amp with a dummy load as a "distortion pedal".

I've made something similar - 'inspired by' would be a better description...

http://www.youtube.com/watch?v=V2POQEkInmw

I gigged with this little Champ slaved into a Plexi type amp for a while going back maybe 18 months.

[hunter]

Guytron GT-100

EL84 Class A stage in the preamp, feeding into a Class A/B power amp 100W 4xEL34

http://www.guytron.com/images/manuals/GT100-Tubechrt-060628.pdf

[jpfamps]

Guytron GT-100

EL84 Class A stage in the preamp, feeding into a Class A/B power amp 100W 4xEL34

http://www.guytron.com/images/manuals/GT100-Tubechrt-060628.pdf

That's quite an interesting circuit as it uses a transformer for the EL84 stage, rather than resistive loading.

My guess is that this would be deemed excessively costly to the average manufacturer.

There are a few amps that use a transformer PI (eg the Fender Musicmaster).

I thought it might be an interesting idea to use an EL84 combined with a transformer in single ended configuration as a PI, but it's never got off the drawing board.

[hunter]

That's quite an interesting circuit as it uses a transformer for the EL84 stage, rather than resistive loading.

My guess is that this would be deemed excessively costly to the average manufacturer.

Well, he surely passes that cost on to the client.

The Guytrons are very highly regarded though, as you get that AC30ish compression/mid thing as well as the EL34/Marshall bite.

http://www.youtube.com/watch?v=itdmuEdhl7M

http://www.youtube.com/watch?v=NKSok9Ohlrk

[Dmoney]

Found some more things in this amp.
looks like the 10K resistor which should be between the heater centre tap has previously burnt out.
it also looks like the heater centre tap is wired to one of the 6.3v wires, and not to the resistor/cap which look like they have both been replaced, although the PCB is still dirty.
the heater wires are throwing enough noise out to make the amp squeal on the higher gain channel, they are heating the valves though. This has been repaired by some place in Romford, and some old dude in Brighton... although I dunno who did what to it in the past.

[jpfamps]

My guess is that a power valve shorted screen to cathode, and thence cathode to heater thus imposing the HT on the heater winding.

This wouldn't have done the 10k resistor a lot of good......

Can you do the usual 100 ohm resistors to ground either side of the filament supply?

[Dmoney]

well... i just fixed it!
all those wires look like they used to be in some plastic connector. The heater wires had been pulled out and wired directly to the back of a PCB mounted octal socket.
the centre tap was then wired onto the pin which would have made it like the drawing above... the wrong pin formerly in the connector... however... it looks like that pin has burnt at its base, and doesn't conducted. So i moved the centre tap over to the pin connecting it to the new 10K and cap someone else has put it, and it worked!

so it was actually like the centre tap was not attached to anything, and this was making the heater wires beam out noise like there was no tomorrow, and that was getting picked up in the preamp valves and ended up as high F squealing when enough gain stage were in circuit.

I might pop and see you soon with an EL84 that could do with testing... i might also buy an EL84 of you. ha.