tube question

[Reece]

Coot has it. Tap each tube in turn and you should localize it. The answer is a new tube, but you can often silence a microphonic tube with extra weight attached to it, which modifies its mechanical point of resonance. A way old timers did it (thank you, thank you) was to wind a number of turns of heavy solder around the tube envelope. Then slide it off, tighten up the turns a bit, and slip back on so it stays by its own pressure. Looks funky but usually works.

[old_coot88]

Originally Posted by Reece

...A way old timers did it (thank you, thank you) was to wind a number of turns of heavy solder around the tube envelope. Then slide it off, tighten up the turns a bit, and slip back on so it stays by its own pressure. Looks funky but usually works.

Some early TV tuners used a lead shield on the mixer/osc. tube to quiet down the microphonics. Without it the oscillator tended to "FM" like crazy with every click of the detent.

[radio nut]

well, I replaced the bad tube,found an out of tolerance resistor and a dead resistor in the tuning eye circuit. Tuning eye is good now. I still think the fm sounds slightly out of tune. The rider's info says that the discriminator transfomer has a calibration to it. The picture of the chassis does not show a transfomer for it and neither does the electrical diagram. The 6h6 disc. tube is good and the resistors and caps around it check fine.If I hook a cd player to the phono input it is extremely clear and sounds great. Is the circuitry just not able to get the fidelity I am thinking I should get?