So I've got this SVT CL in for repair , and someone's had a go at it in the past I see (tell tale leftover scorch marks on the Fil transformer 6.3VAC lead going to the power tube board (see picture). Whoever looked at it previously obviously cleaned up the board and put 220R 1W Rg2s in (I could detect faint traces of alcohol cleaning marks), but they didn't replace the scorched heater insulation wire.
So today - in between jobs, I thinking, hmmm... could these carbon traces on the wire present a potential short circuit problem:
a) to the other components on boards or
b) in terms of a bad experience with the filament transformer itself
I don't know the full history of this particular amp, but before he brought it in to me, the owner tired to replace a full set of output tubes and ran into biasing problems and it died. I managed to resurrect the power (diodes in the +/-15V power supply for the bias sensor circuit had shorted, so I replaced all of those and the filter caps there and its powering up again, and it can withstand all the pre-amp tubes being loaded in it (1.5A) (but I haven't started to load up the 6550's yet and they are 1.6A each).
The colour of the filament transformer 6VAC lead worries me slightly.
Was it just collateral superficial coloration from a (likely) previous Rg2 fire (it seems to be on the wrong side of the board for an Rg2 fire don't it?)?
Or was it the filament transformer itself?
Why would only one lead be dirty?
I can try putting in an inline 15A fuse on the fil transformer secondary - which would at least possibly help to isolate the problem a bit. Trouble is that to order a new fil tranny here is about $500+ just for the part, and the owner seems to think the amp was working fine before he tried to put the new 6550s in.
Or should I just chuck some heat shrink over that scorched wire insulation?
Opine away...
So today - in between jobs, I thinking, hmmm... could these carbon traces on the wire present a potential short circuit problem:
a) to the other components on boards or
b) in terms of a bad experience with the filament transformer itself
I don't know the full history of this particular amp, but before he brought it in to me, the owner tired to replace a full set of output tubes and ran into biasing problems and it died. I managed to resurrect the power (diodes in the +/-15V power supply for the bias sensor circuit had shorted, so I replaced all of those and the filter caps there and its powering up again, and it can withstand all the pre-amp tubes being loaded in it (1.5A) (but I haven't started to load up the 6550's yet and they are 1.6A each).
The colour of the filament transformer 6VAC lead worries me slightly.
Was it just collateral superficial coloration from a (likely) previous Rg2 fire (it seems to be on the wrong side of the board for an Rg2 fire don't it?)?
Or was it the filament transformer itself?
Why would only one lead be dirty?
I can try putting in an inline 15A fuse on the fil transformer secondary - which would at least possibly help to isolate the problem a bit. Trouble is that to order a new fil tranny here is about $500+ just for the part, and the owner seems to think the amp was working fine before he tried to put the new 6550s in.
Or should I just chuck some heat shrink over that scorched wire insulation?
Opine away...
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