Dead amp, dead amp, dead amp dead amp dead amp dead amp dead aaaaaaaamppppp :(

PolarityMan

My JVM died again only a year after replaced valves and a couple of blown resistors back in Aug. Was working fine then cut out with no noise whatsoever coming from the speakers, even on gain channels with volume cranked not even getting the usual hiss.

Looking that the valves through the grill I could see 2 of the power valves were definitely glowing more than the other 2 but I do think all 4 were glowing (although can confirm that once I try it in a better lit environment).

Any ideas what could be wrong this time?  Is it likely that there was an underlying fault last time that wasn't caught?

Kind considering moving it on once it's repaired and getting something else tbh.

Jalapeno

Whereabouts are you ?

Marshall factory in Bletchley/Milton Keynes do repairs.

DJH83004

I would suspect it is the HT fuse that has blown, possibly caused by one of the output valves flashing over internally. Its a while since I looked at one, but I believe the fuses are mounted on the pcb. That would be my first port of call. 

PolarityMan

DJH83004 said:

I would suspect it is the HT fuse that has blown, possibly caused by one of the output valves flashing over internally. Its a while since I looked at one, but I believe the fuses are mounted on the pcb. That would be my first port of call. 

Wouldnt a fus blowing stop anything working? The lights all come on, I can hear the mechanical channel switching clicks and the tubes do light up

Cirrus

PolarityMan said:

DJH83004 said:

I would suspect it is the HT fuse that has blown, possibly caused by one of the output valves flashing over internally. Its a while since I looked at one, but I believe the fuses are mounted on the pcb. That would be my first port of call. 

Wouldnt a fus blowing stop anything working? The lights all come on, I can hear the mechanical channel switching clicks and the tubes do light up

No, the HT fuse only stops the high voltage part. Most amps run the front panel lights, relays for channel switching, valve heaters which are the bits in the tubes that glow orange etc from other lower voltage transformer taps with separate fuses.

PolarityMan

So sounds like I should try replacing that first and see if it blows again before taking it to a tech

guitarfishbay

O [lack of] fortuna?