ampeg b-25 bass. smoking resistor

[lstead]

hi, i have this Ampeg B-25 which is smoking the 1K 2W resistor next to the power caps. i have replaced it and the 2 30uf 600v caps and it still smokes under heavy playing.....not when idling. any thoughts anyone???? thanks, laurie
ps. i also put new 7027 tubes in....no change!!!!

[loudthud]

The schematics I found for the B25{nothing} show a 470 ohm 2W for the screens and a 1K 10W for the preamp. The schematic for the B25B show a 1K 2W for the screens and a 1K 10W for the preamp. If the 1K 10W was smoking, I would suspect the multi-cap for the preamp has leakage. If it's the screen dropping resistor, check the bias, if it is OK, try a 5W 1K.

[lstead]

i tried using the unused 40uf line on the multi cap [it has 3, uses 2] no change. the schematics diagram on the amp itself shows a 10K/5w and a 1k 2w [the smoker!] is it worth assuming the the multi cap is leaking and replacing it?

[loudthud]

I just dusted off an old B25 I have and the 1K 2W is burned up. It's the one between the 'A' and 'B' nodes on the schematic. That's the screen droping resistor and is not affected by leakage in the big can cap. If you play the amp with lots of overdrive that resistor will probably smoke. I'm tempted to put a 5W 'sand box' part in there and move the big cap next to it to the other side of the PCB. Mount the resistor off the board by about 1/8 inch to give it room to breath. The amp seriously needs a mod to adjust the bias.

[lstead]

that's the one!!!! i noticed that it really started smoking when the amp was overdriven so i am going to put in a 1K 5W and see..........thanks for the update, laurie