How Bad is my Bassman Cooked ?!?

[Birdy]

Okay...Buddy hooked up a THD Hotplate into my just re-done '68 Bassman
head wrong...plugged into the line out input instead of the speaker output on the back of the Hotplate.

Amp volume was on 9. Light show flashed from back of head(tube gas ?), no smoke, no smell. Amp was hooked up wrong for about 10 seconds.

Amp now pops a bit, sometimes just hums with no sound until you turn it off, then on. Last night it cut out in mid song and just hummed. Rear fuse did not blow. Hotplate is fine. Amp does it with or without Hotplate, both channels.

All tubes lightup normally, just hums though thru speaker cab. All tubes(JJs) were done as amp was recently completley done.
I'm thinking the powertubes are cooked ?
Any suggestions ?(Besides not letting beer drinking buddies hook up my amp ?)

[scopeboy]

It does sound like you Foobar'd the power tubes. The light show was probably the screen grids getting melted. I would replace them, and if it still messes up, replace the screen resistors too.

[Rossl]

It does sound like you Foobar'd the power tubes. The light show was probably the screen grids getting melted. I would replace them, and if it still messes up, replace the screen resistors too.


Soundslike a good suggestion. I would open up the amp and see if anything if fried. There should some signs of something burnt. You should also be able to see if the tubes are damaged.

I would also check the the PS caps and take some basic voltage readings.

[VacuumVoodoo]

Check also tube sockets for traces of arcing, both on top of chassis and inside. These are black traces between pins. Same on tube bases. If there's evidence of arcing replace the sockets.
Your output transformer could've taken a beating too (that's the worst case scenario) so have it checked as well.

[Birdy]

Thnx for the input guys, muchas gracias :AOK

[Johnny Z]

A few things come to mind I'll try to put then in the order of most likely to least.

1. A bad cable.

2. A bad tube, most likely a Power tube, try a known good 6L6 in each socket or better yet get the tubes tested, a faulty plate or screen such as an open circut could cause cutout in operation. A short would blow something like the screen grid resistor and fuse. Just because a tube lights don't mean it's good.

3. A bad connection between the output Tranny and the power tubes or worse a bad tranny.

4. A stupid friend who didn't know what he was doing and now you're screwed. (I just had to add that, no offence)

RULE #1
I would never let anyone hook up anything to my amp without knowing what they were doing.

RULE#2
Never start out with your amp cranked with things like that, and I don't even recommend using them as a general rule.

Good luck I hope you get it working soon.

[Birdy]

Thnx Johnny Z.
My buddy is comming clean with new tubes and whatever the bill is.
Lucky me, I know other guys that this has happened to and it's like
"whoops", and they have to pay for it all, all over again.

[Johnny Z]

Thnx Johnny Z.
My buddy is comming clean with new tubes and whatever the bill is.
Lucky me, I know other guys that this has happened to and it's like
"whoops", and they have to pay for it all, all over again.

He's a friend in deed.:BEER