Trace Elliot speed twin gone bang

[TFI919]

Newbie question:

I bought a Trace Elliot Speed Twin C100 on ebay, and as soon as I got it home and turned it on (after warming up obviously!) sparks were evident from a vent above the preamp pcb.

The sparks stopped pretty quickly, and there was still some background noise from the speakers (background noise sounded similar to dirty volume pots) but no volume from the guitar.

The power valves still glow, and I can still hear the background noise, but no guitar! Having looked at the 5 12AX7s in the preamp (these are situated below the PCB so I can't imagine that I would be able to see sparks from them from above) only one of the 12AX7s glows.

There are a couple of things I may have done wrong and would appreciate any help anyone on here could give me:


- This amp has a switch allowing either El34 or 6L6 valves. The switch was in the El34 position (as it was when i received the amp) but the valves fitted were Sovtek 5881's - which I now understand are actually 6L6 alternatives.

- The speaker impedance sitch was set to 8 ohms, and the speakers are 16 ohms wired in parallel (I think this is correct, but thought I should check)

- My guitar cable went into the OUTPUT of my tuner, then the INPUT of my tuner went to the INPUT of my effects pedals which went to the INPUT of the amp. I can't see how this could affect anything, but it made my head hurt and I thought I had better check with the experts!


I would appreciate any and all help that anyone can give, as I am now amp-less for rehearsals this week and have a gig coming up too!!

Thanks in advance,

Toby

[steve]

Toby,

I can't help you with the techical problems, but I have the schematic and will post it in this message.

Is the attached schematic the right one?

steve

[TFI919]

Thanks Steve,

At least I can give this to someone more experienced along with the amp itself to repair!

Toby

[Mars Amp Repair]

hello,
not certain if you've gotten all your answers by now...just stubbled on your post. If this is a Speed Twin, the preamp tube filiaments are wired in series...meaning if one goes out, some of the others depending on how it's all wired, will also go out.

This amp as I recall has a propensity for the regulator IC to run VERY HOT to the point of unsoldering itself. The one in particular has a black heatsink on it & another one piggy-backed on top of it (for obvious reasons). That might not be a bad place to start.

As I recall they have a couple of 470 ohm resistors in parallel with each other & in series with the preamp tube filiaments. You'll probably see that they have blackened the board near the first 12AX7 & probably unsoldered themselves, too. That would be your preamp filiament issue. I'd replace them with higher wattage resistors (like 2 or 3watt cement types) & stand them off the board. Really dumb in my mind to try to drop filiament voltage with resistors.

BTW, the

I also had shorted rectifier diodes & a blown power transformer in the one I worked on. The new power transformer rans extremely HOT. I never found anything that was causing excessive current draw & had to figure that is that way it was designed. It never came back.

Hope this helps....glen