Ampeg VL-503 Blowing Fuses

[pastorking]

My Ampeg VL-503 keeps blowing the 1 amp slow blows that help protect the tubes. I put in a new fuse and it immediately blows. The tubes have checked out to be fine.
Anybody got any ideas?

[52 Bill]

Anybody got any ideas?

If it's not the tubes, then it could be a bad transformer, a shorted cap, a shorted diode, anything really.

If you remove the tubes and power it up does the fuse still blow?

[Enzo]

And how did you check those tubes. I agree, the tubes are by far the most likely cause of fuse blowing.

[akillian]

Hello Partorking

I get the same problem...

It start with an awful general sound of the amp when i was playing... i tryied to play with the bias of the tube, and then it blown a tube and the fuse...

i have retubed the all amp... both stage, preamp and power... replaced the fuse...
switched the amp on with the bypass on, ... everything ok... i have let it warm, and when i switched off the "by pass"... bang, the fuse has blown !

Same amp vl 503... did you solve your problem ?

it would help me a lot...

regards,
Edouard

[Chuck H]

It sounds like these amps may have an issue with the bias supply. Since the OP's tubes test OK (though IME this doesn't always mean they are) but is blowing fuses and akillian's amp blew a tube and a fuse when he messed with the bias. And then blew the fuse after installing new tubes.

pastorking and akillian, you need to pull the tubes and take a DC voltage reading at pin 5 of each power tube socket and report back.

If you don't know how to safely work on tube amps, there can be lethal voltages present even with the amp unplugged, take it to a qualified tech.

Chuck