by 77seriesIII » Fri Feb 15, 2008 2:23 pm
Bummer, really excited took my amp over to Hembrook's house and we were going, going being the key phrase, have an amp taste test. I have 300Bs, simply changed the r19 and r20 resistors to 1.5Ω. I was running SS rectifier but had switched back to tube a few days earlier, I like glowing tubes.
Anyway plugged in the amp as as it was warming up hum started on the speakers, and got louder as the everything warmed up...Me staring at my amp thinking WTF I dont get hum at my house. I hit the power switch to turn it off and just before getting there C5 let the magic smoke out. I was able to replace c5 there, but the hum is still there, real loud like, both channels. I removed all leads from the board and then I tested all the resistors and got accurate readings for each one but had to remove R21 to get a good reading. but once removed r21 read ok. Freakin useless now but I know it is good. I have a spare so no worries.
What is the next step? What are some other things that may have let the magic smoke out? Should I replace the c6 as well? I have no way of testing my 300bs but may be able to find a place that can, is it even worth testing based on c5 letting lose? What about OPTs would they have been damaged? I touched both OPTs and power tranny just after the cap let loose and none of them were even warm. Doesnt mean much but...
The amps in pieces now, checking all solder joints, crimps, etc will be piecing it back together over the weekend.
Any help out there? Ideas on what to check next?
Much appreciated
erick