01-20-2012, 08:14 PM
Hope someone here can help.
I have a Philco 42-395 with a bad power transformer. I found a power transformer in my parts collection that would give me the needed 6.3 fil Volts as well as the center tapped HV windings for the 7Z4 rectifier. BUT, the HV should be about 300-0-300 and this big transformer puts out 385-0-385. It also had 5V windings which I taped off.
I installed the transformer and brought the set up on a Variac (set is fully recapped). It plays fine but after a while the 7Z4 shorts out and shows a cathode short or a plate short or both on my tube tester when I re examine it. ; usually the next time I turn the set on. I've gone through three 7Z4 rectifier tubes and thought the smart thing to do now is ask for help.
Is the HV from this transformer the likely culprit? Is there a way to lower the HV to around 300-0-300 without also lowering the filament voltage which is right where it should be?
How dumb was I to try to use this transformer in place of the original? It's the closest thing I have with enough beef to put out about 4-5amps filament for the 9 loctal tubes...
Thanks for any help or insight.
Here is the schematic.
http://www.nostalgiaair.org/PagesByModel...013537.pdf
Mark
I have a Philco 42-395 with a bad power transformer. I found a power transformer in my parts collection that would give me the needed 6.3 fil Volts as well as the center tapped HV windings for the 7Z4 rectifier. BUT, the HV should be about 300-0-300 and this big transformer puts out 385-0-385. It also had 5V windings which I taped off.
I installed the transformer and brought the set up on a Variac (set is fully recapped). It plays fine but after a while the 7Z4 shorts out and shows a cathode short or a plate short or both on my tube tester when I re examine it. ; usually the next time I turn the set on. I've gone through three 7Z4 rectifier tubes and thought the smart thing to do now is ask for help.
Is the HV from this transformer the likely culprit? Is there a way to lower the HV to around 300-0-300 without also lowering the filament voltage which is right where it should be?
How dumb was I to try to use this transformer in place of the original? It's the closest thing I have with enough beef to put out about 4-5amps filament for the 9 loctal tubes...
Thanks for any help or insight.
Here is the schematic.
http://www.nostalgiaair.org/PagesByModel...013537.pdf
Mark
