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My bandmaster has started crackling continuously once it's warmed-up (after about 20 minutes).

Does this indicate any particular valve is screwed, or could it be any of them?

Is this during play, sitting there but on, on standby?

Hmm.

Could be either preamp or power amp valves. Have you got any spares lying around?

It does it while sitting there, doing nothing. The power valves are the two 6L6s right? Unfortunately I aint got any spares. Think it's worth buying some to check?

timhulio wrote:It does it while sitting there, doing nothing. The power valves are the two 6L6s right? Unfortunately I aint got any spares. Think it's worth buying some to check?

I would say so, as expensive as they are, it's always a good idea to have at least 2 spare preamp valves and a spare set of power amp valves lying around.

Ah the crackling happens on both channels. I wonder if these use the same preamp valves?

They'll definitely use the same power amp valves.

How many preamp tubes are in your bandmaster mate? I'll look for a schematic.

OK that was easy:


They have a 7025 each and then share the 12AT7 Phase Inverter. The 12AX7 is fine as that's vibrato only and wouldn't affect the Normal channel.

So it points to the 12AT7 or the two 6L6GC's.

I would get a replacement valve set anyway, it might sound boss if you replace them. There seems to be a 10K bias point, are there bias probe points on your amp?

I looked on the Fender Amp Field Guide and it reckons:

Normal: 7025
Vibrato: 7025 and ½ 7025

Schematic says no.

There's probably a bunch of different circuits.

Can I swap the power valves without rebiasing? I'm not entirely sure what that entails!

You should probably be ok if you get some by the same manufacturer and a matched pair.

Mike wrote:Schematic says no.

There's probably a bunch of different circuits.

doesn't he have a bandmaster reverb?

That makes more sense. Bubbles to the rescue

I would look at the rectifier tube also, since it is common to both channels. You have my Super Reverb in a head basically.

Thanks chaps. I'll try the power tubes first, since I've just ordered some. If that doesn't work I'll swap some more at random til it does. Luckily it shares all the other tubes with the Deluxe Reverb I've got.

Oh noes. It's none of the tubes- I swapped em all: new power tubes, and swapped the others with those in the Deluxe Reverb, which I know are fine.

What else could it be? What do bad filter caps sound like?

That, or a dirty jack would be my next bet. Drop LDC a pm to direct him back to this thread - guy is the Fender BIBLE.