Bad caps???

N

Nigel

Guest
My amp's gain channel will play fine for a while, then it sounds all thin and the tonestack/master volume quit working. Clean channel is fine.

Is this what happens when caps go bad??? It's got those surface mound yellow-box MEB style ones. I replaced one that was faulty with an orange drop and noticed a BIG tone improvement.

It plays fine as long as it's out of the shell and upside down so heat can escape. If I put it right side up like it's in the head, the gain channel fizzes out in minutes.

I think I have a bad cap that self heals when it cools off.
 
I usually, find the problem you describe to be a preamp tube. It's very uncommon for the caps you described to go bad. The caps that go bad are electrolytic caps, not the film caps you're describing.

I would try tubes first, if you have not already. If not that you might have a cracked solder joint, or cracked resistor.
 
CNutz":2ssagtas said:
I usually, find the problem you describe to be a preamp tube. It's very uncommon for the caps you described to go bad. The caps that go bad are electrolytic caps, not the film caps you're describing.

I would try tubes first, if you have not already. If not that you might have a cracked solder joint, or cracked resistor.
Click to expand...

Thanks bro.
 
I would be 90% sure it was a preamp tube. I have never heard of a cap doing that.

Also, cnutz is right electrolytics are the ones that need replacement, not film caps.

Having said that, a cracked joint could do that, but it's most likely a preamp tube issue.
 
My 50's f series (91/92) Blackburn Mullard long plates are straight.

The soldering had cracked under that yellow box cap. It's a total bitch to get the board out, so I just pulled it and resoldered the orange drop I'd put in there, and fixed another resistor. BOOM! Success.
 
Good deal! That's the down side to PCB's. I have a 92 VHT pitbull that I had to go through and fix cracked solder, and that board is a real bitch to get out.
 
It's back...whole tone stack goes out, only gain knob works. If I pull it from the chassis, and tap on the PC board around three relays, it happens. If I change back to the clean channel, then change back, it works until I tap the board or relays.

Bad solder joint? Failing relay?
 
Yeah, sounds like a bad relay. Replace them, and as an extra measure I would touch up all the solder joints around that area.
 
CNutz":1jwcwa1y said:
Yeah, sounds like a bad relay. Replace them, and as an extra measure I would touch up all the solder joints around that area.
Click to expand...

It's on the back of the board...gonna be a sumbitch to do this!
 
Yeah. Make sure to discharge caps, and your going to need a solder sucker (if you dont already have one) to suck the solder out of the holes so that the relays can be removed.
 
Per Bruce, someone replaced the signal diodes with the wrong parts. Getting some 1N4148's from Tube Depot here shortly, will report if winning happens. Fingers crossed!
 
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