| Author | Message | ||
     pguid |
First I want to say thanks for this awesome site. It has helped with my collection of MM amps. I recently purchased a 112 65 with EL34 tubes. I noticed the tubes ran hot (cherry in hi mode). I tried to adjust the BIAS (to.5) and I noticed the voltage creeps up and the tubes get red hot (I quickly power off the amp). I want to start by replacing the BIAS pot and the 10Ohm cathode resister (very discolored). The amp seems to work well on low however; the tubes run hot (a bit red). I also replaced the driver tube and tried a set off slightly used tubes I had around. Any other suggestions would be greatly appreciated? | ||
| michael kaus |
THe bias caps on those amps are getting old and shouyld be replaced. They could be the cause of your bias voltage problem. If you go to that much trouble(AND YOU SHOULD) replace all the electolytic caps and be done with it but be careful, there are 700 volts bouncing around there. The bias pot is NOT the likely cause. You need to check your bias supply voltage with the tubes out at pin 5 of the power tube socket and see how much negative voltage you have and if it is stable. I'm betting the bias caps. | ||
| pguida |
Thanks Mike, I'll try replacing the BIAS caps. I'll post the results when I'm done. |