Internet amp tech help: no valve lights or heat

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Re: Internet amp tech help: no valve lights or heat

Post by Bg »

tubeswell wrote:BG said it earlier. If the heaters aren't glowing, the tubes won't conduct.

Its a power supply problem (of some kind), and it probably needs a good overhaul.

If its a blown fuse, that will be because some part of the power supply circuit after the fuse is drawing too much current - and merely replacing the fuse won't fix things. My guess (from this distance) is that one (or more?) of the filter caps is shorted. I'd say all the caps (including the bias supply caps) are probably overdue for replacement. There could be other problems related to the power supply. Only way to find out is pull it apart and starting metering everything. Try taking some DC voltages at the various power supply filter cap nodes. Look for cooked/exploded components.
Yep this, I should have added in my post that fuses don't blow from old age :) There is always a reason, even if the reason is the wrong fuse type.
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Re: Internet amp tech help: no valve lights or heat

Post by Single coil »

Yeah fuses are funny.

I’ll look for cooked shit when I have it in bits again. Unsure how far away this will be.
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Re: Internet amp tech help: no valve lights or heat

Post by RectifiedAmps »

I've seen this same issue with a ValveKing recently - the DC-powered heater/filament circuit was to blame in that case. Although the heater fuse was blown, two of the four diodes in the rectifier section were also shorted and needed replacing. Not sure if a power tube short pulled too much current through them before the 3A fuse blew or if they just died. Peavey uses 1N4003 diodes, which are rated for 1A max - pretty close to the 0.9A that 6L6GCs typically draw during normal operation. Not a smart idea in my opinion, so if you have to replace them use something with more current handling.

Hopefully your issue is just the fuse, though.

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Re: Internet amp tech help: no valve lights or heat

Post by RectifiedAmps »

Also, the fuse you want to check should be labelled F203 on the board - it'll be a 3 amp slo-blo/time delay fuse.

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Re: Internet amp tech help: no valve lights or heat

Post by Single coil »

Ain’t it a fucker you’re at the other end of the country! :lol:
werdna wrote:Well at least I can still make toast in the bath without anyone telling me it's unsafe.

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