Zenith am/fm Stereo problem

8/5/2006 12:28:23 PMElton

This is a model SL2505 floor stereo from the sixties , phono plays well but the FM has a bad hum like a e-cap has gone bad , and the AM is dead no nothing not even a click , I have not dug to deep yet I have checked all the tubes except the 19GQ7 my old jackson 648 does not list this tube , the tube is defined as a triple diode AM detector and a FM discriminator, since I cannot check this tube and I have no subs for it should I try a replacment first before ripping into the chassis or has anyone had a simular problem that might be causing the hum and dead issue?
Thanks
E.

8/7/2006 1:34:43 PMThomas Dermody

doesn't take much to detect a signal all you have to do is test the diodes for basic action on your tube tester i have had many diodes that work fine even though they test in the replace region not much current flows through them for detection make sure that they're not gassy thomas

8/7/2006 2:37:56 PMElton

I would test it but as I said no way to test it with my old jackson the filiment won't even light up with it, in the radio it lights up very bright so bright that it looks like it has a internal short? would anyone have settings for this tube to be tested in a jackson 648?
Thanks
:doesn't take much to detect a signal all you have to do is test the diodes for basic action on your tube tester i have had many diodes that work fine even though they test in the replace region not much current flows through them for detection make sure that they're not gassy thomas

8/8/2006 9:02:40 AMThomas Dermody

Ah. It might have an internal filament short. Strangely, I have had quite a few Zenith tubes with this problem.

Not quite sure what to do with your tester. I assume that it doesn't have typical pin levers. Perhaps, in order to get the filament to light, you should adjust the tester like you would for another tube with the same pin-out. Just don't press the merit button. If your tester uses a constant current system instead of a voltage regulated system, the tube might not light if it has filament shorts (depending upon how the tube is wired internally...parallel filaments won't light...series ones will).

Thomas