RockerVerb 50 blowing HT fuses

[DoyleFan]

Blowing fuses with NO POWER TUBES in. Very strange. This happens intermitantly, and when it does the plate voltage drops to around 200 volts. I have replaced the on/off/standby switch. I'm drawing at straws. Any help?
Thanks,
doylefan

[hasserl]

Got a schematic?

Does the amp have a rectifier tube? That could be the culprit. If not, there is a short circuit somewhere on the PT secondary HV circuit, it could be the power transformer itself.

[Enzo]

I think so too. Disconnect the center tap wire from the output transformer. Now watch the B+ and see if it still sinks. if not, then the output transformer may well be bad. If the B+ still droops to 200v with the transformer disconnected, you more likely have a failing filter cap or an arc somewhere like a tube socket.

[PlinytheWelder]

Schematic is here:
http://www.shortscale.org/forum/view...6a24c523219363

[DoyleFan]

thanks guys, i'll try these suggestions now and let you know how I make out.

[DoyleFan]

I think I tracked it down to C5 (filter), I'll try replacing it. Tough because this is an intermittent problem.

[DoyleFan]

No luck. seems to be ok when i disconnect the choke. strange because I disconnected the preamp, removed the power tubes, lifted the bias circuit to isolate the problem and it's still there. You can see the fuses arcing inside.

[Alex R]

- just had this same problem. On this amp it was caused by C3 shorting out. I put new fuses on, fired it up on the light bulb and traced it by the smoke .

I'll put the schematic page on here.

So what's C3 for?

[Enzo]

Transient suppression.

[Alex R]

Thanks Enzo. It looks like an accident waiting to happen sitting there, but (here comes the confession) as I haven't quite fully grasped cap-fed bias I didn't know whether this was some strange permutation of it, so instead of binning it as I was tempted I replaced it with a 1kV. Couldn't read the rating of the little burned blue disk I took out. Maybe it really did get a transient!

There to satisfy some safety reg. or other I guess?

[Enzo]

Or noise.

[janne]

..

sorry to reopen this..

I am having something similar.. Blowing HT fuses constantly.
Have umplugged the Choke to confirm the 1st section and the TP6 to completely eliminate the transformers etc.

I am coming up with Cap 5?

Thoughts?? Is this common?

Thanks

Janne