| Author | Message | ||
     Vito |
hi, I got a 212 HD One-thirty. I think it needs new tubes, cause the old ones seem worn out. Can I just buy usual EL34 tubes (like in Marshall-Amps) or do they have to have special features? I now how to measure the bias, but I can't find the pot where to adjust it. Could somebody tell me? That would be great! :-) Thanks and best regards, Vito | ||
| Michael Kaus |
Do you have the model with the 12ax7 PI tube? If not, the amp is a quasi cathode bias amp. If you have the tube, the bias adjust pot is on the main circuit board on the end closest to the power trans. If no 12ax7, the setting procedure is here on the sight somewhere by measuring the voltage on the cathode resistors and adjusting the small pot on the driver board. Mike. | ||
| Michael Kaus |
Forgot to add that if you do have the 12ax7, you should either get NOS tubes or maybe the JJ version of the E34L's. Also, bias them at 15mA-not 40-45 like the other EL34 amps. THe high plate voltage of the MM amps restricts how high of current you can pass. I use the JJ's and have tremendous succes with them. | ||
| Vito |
Hi Michael, thanks for the Info! So in any case the Chassis has to come out of the cabinet - so I'll look for the pot. In deed I got the version with the 12ax7-tube. I'll measure the bias with a kind of thing that comes in between the tube and the socket with a cabel that comes out of it. And I got a company here that sells JJ-tubes for a very reasonable price - so I will get them soon :-) Where are you from? I'm from Germany. best regards, Vito. |