Bandmaster Reverb Issue

[talldavid]

Hey Everyone,

I found this site through Weber's site the other day and read through some posts, and wanted to see if anyone might have some pointers about my Fender. It's a late 70's (maybe '76 or '77) I'm the original owner and it's 100 % stock. The problem is that it blows the reverb tube as soon as it starts to warm up...like after 20-30 seconds.

Before it blows, you can hear reverb, then it blows and when you turn up the reverb volume, there is alot of nasty crackling noise. So, i just turn it all the way down. Everything else is great, just put a new set of Winged C tubes in and it sounds sweet. I called a couple of local repair guys but they wanted <$200 just to look at it.

Any thoughts about what might be wrong?

Thanks,

David

[soundguruman]

The reverb driver transformer can short or other related parts may be bad also, like the cathode bypass cap for that stage could short..
I don't usually charge more than $75 labor + parts to just "fix" a thing. But there is rent to pay, and that can be high.
but it can read good, and then when the power is on, it shorts, or it could be shorted all the time.
You will find the number on the driver transformer and try to find the correct replacement. A Fender dealer or Fender parts center will get the right one for you..
if that reverb driver transformer primary shorts, conceivably, it could blow the drive tube. If the secondary wiring is open, it may cause a problem. If the cathode bypass cap shorts, it could conceivably draw too much current.

[talldavid]

Thanks Soundguruman,

Normally I would just take the amp in, but I can live without reverb for now. Frankly, working on an amp is something I've never done and I don't want to screw something up...or kill myself for that matter. If something else were to go wrong, i would definitely take it in for servicing, I just can't afford to spend the money to fix the verb.

Are replacing/troubleshooting those parts fairly straight forward? I really want to learn how to work on my stuff and even start building kits...

[soundguruman]

It's really pretty dangerous to try to work on it, even when it's un-plugged, it can hold a charge of power in the capacitors.
That's why you let the tech get shocked, instead of you.

[nickb]

First remove the offending tube! Power on, warm up, standby on, power off (leave standby on). Leave for five minutes. This will bleed the caps so something safe.

If you are careful you and have thin probe tips on your meter you can probe the socket of the bad tube. Connect the negative to the chassis and the positive to pin 3 check the resistance it should be around 2.2k ohms, if too low the bypass cap is bad. Next power up and switch to a voltage range and check pin 2, it should be close to zero volts, if is positive then the coupling 500pf cap is bad.

I'm having a hard time imagining that the transformer is bad if you got reverb for a ew secs and I don't think a bad transformer will take the tube out under no-signal conditions.

[Enzo]

What does "blows the reveb tube" actually mean? What exactly happens? The tube heater gets bright and burns out? The tube shatters? Sparks fly inside it? Outside it?