Zenith 7h822-z tubes not lit

[old_coot88]

A vital factoid to hardwire unto one's knowledge base is this -

Series = constant current

Parallel = constant voltage

To elaborate, in a series string, constant-value current runs thru every element of the string. Voltage across individual elements may vary depending on each element's resistance.

In a parallel setup, constant voltage is across every element, though current thru individual elements may vary according to each element's resistance.

[Tennangler]

I looked up the pinout after I wrote. Should have done that first. I checked continuity across pins 3 and 4 and it was open. A friend with a tube tester tested it as bad. He told me a 35c3 he has will be a replacement. I was reluctant to use it but tried it anyway. The radio came on but has a hum. The hum does not vary with the volume control.
First, is it ok to use the 35c5? Second, if it is does the hum indicate a grounding issue?

[old_coot88]

Originally Posted by Tennangler

First, is it ok to use the 35c5? Second, if it is does the hum indicate a grounding issue?

35c5 is a different pinout and wouldn't work without rewiring the socket.

https://www.radiomuseum.org/tubes/tube_35c5.html

35f4 would be a drop-in but most likely unobtainable

https://www.radiomuseum.org/tubes/tube_35f4.html

Hum is bad filter capacitor(s).