Name:    Justin
Email:   justnd@localnet.com  
Subject: tube noise, volume loss
Thread:  201
Time:    Mon, 15 Oct 2001 07:11:40 UTC

Hello, fisrt of all it sounds like a bad tube, but there might be a few other things to check out too. What you could do first is, with the amp running, take something non-conductive, like a pencil, and LIGHTLY tap each ofthe power tubes. If you get the noise when tapping one of the tubes, then this is theproblem. If not, this is highly unlikely, but try a different set of speakers. Sometimes older speakers will develop strange sounds. Also, if it is a tube causing the noise from vibration, this will help to hide it. Most likely it is a tube, and if it is, change them as fast as possible. If your loss of volume is from a shorted power tube, it is bad for your amp to keep the shorted tube in the circut. You should also check into replacing the power capacitors, if ithas't been done. This will help to bring back some of the sparkle, and dynamics that the amp originaly had. For power tubes, I would recomend Svetlanta's. I have the same amp that you have, and I have replaced all of the power caps., screen grid resistors, op-amps,(excecpt for the two that drive the reverb,as new replacement op-amps don't match up with the original reverb tank), had the pots, and tube sockets cleaned, re-tubed it whith Svetlana power tubes, and, or course, had it re-biased. The amp sounds great, like brand new, only with the nice softer, vintage sound that comes from an old output transformer. Also, you did'nt mention if your amp is one with a tube phase inverter (a little tube next to the power transformer, covered with a metal tube shield), if so after you get your problems sovled, you might want to try several diffrent tubes(of the same value(7025 or 12ax7a), of course). You can change the character of the amp by trying differnt phase inverter tubes, even tubes from the same brand, as no two tubes are exactly the same. You will notice a differance when changing from tube to tube, like a smother sound, more bass, more trebles, or the amp might distort sooner. You should deffinitly replace the power tubes if they are bad, but do yourself a BIG favor and bring it to a repair tech, and have him install, and re-bias(adjust the idle voltage of the power tubes, because every power tube has a diiferent "ideal" voltage, it should be adjusted everytime you change the power tubes) the tubes, and if you have the cash, you should really have the power caps. replaced, and if you notice your amp sounds flubby when you turn the bass past 3 or 4, have the op-amps replaced. If you notice that the tremolo acts wierd, there are two transistors that run the tremolo, and an adjustment pot(inside) that should be replaced. The tremolo is suposed to have 2features, from 1 to 5, it's suposed to be like a normal tremolo, from 5 to 6, a second pusle should be heard. Kind of like a rotating speaker, a very nice feature. Any other questions, by all means, feel free to ask. I have spent a great deal of time restoring my 212-HD to as original as possible, and am only happy to share it with others.