Trouble with Bassman

[MysteryFever]

I brought my Bassman head back from a gig about a month ago and shelved it, since I had bought a new amp that was more suitable for what I've been playing.
I plugged it in the other day and I've got a weird buzzing sound when it comes off standby and if I try to play through it, it blows a fuse.
Anybody know what could have happened? It was working fine last time I used it.
I replaced the power tubes with spares and the problem persisted, but when I pulled the power tubes completely the buzzing stopped.
Also, it's SS rectified. Any help is appreciated.

[selloutrr]

fuses blow for a reason.
you can rule out a bad fuse. put it on a variac and meter the amperage as you bring it up to operational voltage. or put in a fresh fuse and let it blow.

next - Filter caps and faulty tubes.

When was the last time the filter caps were replaced?

Did the amp take a hit during travel, a sudden stiff jolt?,or get dropped< damaged tube. It's not uncommon after running the amp all night if you move it roughly before letting the tubes cool it can cause tube failure.

You can test the tubes or replace them with known good tubes.

[brentm]

Have you had a chance to inspect the guts of the chassis and under the filter cap pan?

[Structo]

I would pull the tubes.

Replace fuse, if you don't have a variac you can make a light bulb current limiter.

Monitor the current as you turn it on.

If OK then the culprit is most likely a power tube.

[The New Steve H]

Now that I have a Variac, I have to admit: I like the light bulb thing better. If it's really bright, you know you have a short or something sucking way too much power. If it flickers, you know something weird is happening. If it's totally dark, maybe there's no current draw at all. With a Variac, you don't get all that.

[BTF]

Mys:

I just helped a fellow in PA who had this same problem with his Vibrolux. Hope this helps:

If the amp will not blow the fuse until you play it, and the noise is a BUZZ and not a HUM, turn the amp on, let it warm and pull the last preamp tube (the one next to the power tubes- this is your driver stage). If the buzz stops, then the problem will most likely be localized to your preamp area. If it is here, your most likely culprit will be a leaking coupling capacitor. What you want to do is check for DC voltage on the side of the cap OPPOSITE the B+ high voltage- i.e. the side opposite the tube side of each cap. A small DC voltage leaking through can make a HUGE buzzing sound through a Fender.

If the buzz doesn't stop when the driver tube is pulled, your problem will be in the power section, perhaps a bad filter or leaking coupling cap from the driver tube.

I helped with the Vibrolux over the telephone and until the fellow found the leaking caps (one in the Reverb channel tone stack, one coupling cap) you could barely hear him over the buzz.

Good Luck! Bill.

[MysteryFever]

I feel a tad foolish, but I found the problem and to my utter relief, it was a quick fix. On the rectifier board, the small electrolytic cap had come loose from it's solder joint. Thanks all you guys for your info, I appreciate it greatly!

[selloutrr]

Now that I have a Variac, I have to admit: I like the light bulb thing better. If it's really bright, you know you have a short or something sucking way too much power. If it flickers, you know something weird is happening. If it's totally dark, maybe there's no current draw at all. With a Variac, you don't get all that.

You get all that and more if you bought the correct Variac.

Does your Variac have an Amperage meter? If not you can clip your volt meter to the mains and set it to read amperage. When you bring up the current read the amperage on the meter if it starts to rise or shoot up power down. You have a problem.

[The New Steve H]

My Variac was autographed by Thomas Edison. It doesn't have any of those girly accessories.

I kind of like the light bulb. Very simple.

[John_P_WI]

Variacs tend to vibrate more when there is a short. You will learn the feeling when "turning the knob"....