Loud pop - now no sound...

Chuffola

Just turned on my Vox AC10C1 - usual warm up period then a loudish kind of pop and now.... nothing. The jewel light is lit but not even a hiss if volume turned up full.

Before I open it up - any hints as to what it might be?  Valve (just recently changed these and never have volume above home levels)?  Likely to be pre-amp / power amp valve?  Something more serious?

I'm a total noob so treat me with the contempt I deserve.

jpfamps

Most likely a power valve has shorted and blown the HT fuse which is inside.

Pilot light will still turn on fine, but you will get no sound.

You probably need to change the power valve/s and replace the fuse.

Chuffola

Thanks for the reply.

I've just opened it up. All the valves are glowing and I found the old valves in a box, so swapped them one at a time but still no sound. Not even a hum when everything at 11. 

If a power valve had blown the HT fuse, would the valves still get power?  i presume not, but as I indicated - I'm know very little about amps!

Cheers.

DartmoorHedgehog

The heaters of the valves (the bits that you see glowing) are usually (always?) powered by a different circuit so they'll still glow even if the HT fuse has blown.

stuartm1962

Are the valves lit up?

stuartm1962

If the HT fuse had blown, the valves would not light up. If they are all llit ,i would guess it's a faulty circuit board.

Chuffola

Two entirely different propositions there!  Who's right?

hywelg

stuartm1962 said:

If the HT fuse had blown, the valves would not light up. If they are all llit ,i would guess it's a faulty circuit board.

You've contradicted your own hypothesis there. HT stands for High Tension, and thats the bit that applies 400+ volts to the anodes. HT is not applied to the heaters, they only get 6.3volts from an entirely separate circuit. Quite likely the heater circuit is unaffected, hence why they light up.

ICBM

What jpfamps said most likely - faulty power valve, blown HT fuse. This will still allow the valves to light up orange, but you won't get the faint blue glow that you can sometimes see through the slots in the plates.

Chuffola

Thanks all. 

I'll order valves / fuse later.  Wisdom all round

P.s. Anything I can do to prevent another short or is it just pot luck?

ICBM

Chuffola said:

P.s. Anything I can do to prevent another short or is it just pot luck?

Pure pot luck.

What to do is not change the valves unless you actually need to - the failure rate is much higher with brand-new valves.

darthed1981

Chuffola said:

Loud pop - now no sound...

I murdered my noisy neighbours as well

Chuffola

Just to close this out...

New power valves and HT fuse and all is working again. Thanks for the assistance chaps.