Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on December 04, 2019, 01:44:42 pm
-
6V6 Hammond AO-43 Plexi, turned on amp, played with static, smoke coming from cap can. Opened amp, nothing burnt around can cap, no positive leads touching chassis. Can is relatively new Ruby cheap can 32/32 @500v. Has a bleeding resistor, checked that in the circuit read 0, out of circuit read 220k, it's 3 watts.. Check the both 32uf leads in circuit, both read 95uf bouncing around to 105uf....? The + are yellow and red, the red was sizzling, yellow wasn't, some smoke too when I turned on amp again for a few seconds, no fuse blew. What's next, disconnect wires to can and check again..? The old Hammond AO-43 choke is between the yellow and red tab, being old could it be the choke. How would I tell which is bad?
-
I would replace the can.
-
Thanks, it was the cap. One other question, l added another e-cap, you can see it tied on top of two other caps. It’s the smaller cap, it was suggested to use it as with power on, stby off the rectifier tube wouldn’t get zapped with no filter. Is this cap needed cause l used a rectifier tube. If so, l need to raise it to 500v as with power on and stby off there is 450v on it. That filter runs to hot side of pin 8 on Rect and hot side of stby? That small cap is 47uf @ 450, wonder if that cap might have caused one side of the can to go. Or maybe l don’t need that cap..?
If no stby is used, then no extra cap is needed or SS. But with a stby the rectifier tube has unloaded dc voltage and no filter, that ok?
-
Hmm. Yo have a 47µF cap tied directly to the rectifier tube. Then you have another 32µF cap on the other side of the STBY switch. That puts 79µF on the tube when switched to operate. Not good for the rectifier tube.
-
Never thought about that, 5AR4 has a 60uf max filter, you don’t have a standby switch in your Plexi 6V6. The side of the can that went bad was in series (actually parallel) with the extra 47uf when both switches are open..., yeah 79 uf actually more as the values have a 20% factor. I’ll just take that 47uf out, guess l could put a 100 ohm 10 watt R after the rectifier tube , sag effect... But wonder if that had anything to do with the cap smoking, sizzling...., the can was relatively new.....