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 Post subject: Tube Cross Reference List 6/12 Volt
PostPosted: Sep Tue 21, 2021 3:37 pm 
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Joined: Jan Mon 27, 2020 3:46 pm
Posts: 144
Location: Wilderville, Oregon 97543
Many times I convert a 6 volt car radio by rewinding the power transformer and replacing the 6 volt tubes with their 12 volt equivalent. Sometimes, as with the radio I'm currently converting, a tube does not have 12 volt equivalent. That tube is the 6C4 (µ=17).

Does anyone know of a cross reference list showing 6/12 volt equivalents?

Of course there are other ways to solve this issue but less elegant.

1. Pin for pin 12 volt version (most desirable)
2. Not pin for pin, rewire socket
3. Make an adapter 7 pin to 9 pin and use 1/2 of 12AU7 (µ=17)
4. Replace 7 pin socket with a 9 pin and use 1/2 of a 12AU7
5. Leave two 6 volt tubes and connect their filaments in series (filament currents must be close)
6. Any others???


 Post subject: Re: Tube Cross Reference List 6/12 Volt
PostPosted: Sep Tue 21, 2021 3:40 pm 

Joined: Jan Thu 01, 1970 1:00 am
Posts: 28368
Location: Detroit, MI USA
There is no 12 volt direct replacement for the 6C4. I would rewire the socket and use a 12BF6 with the diode plates grounded, note that you can't leave them floating or you might get background white noise which is difficult to trace the source of. Otherwise 1/2 of a 12AU7, or a 12J5 will work if you want to change the socket. You could also just put a dropping resistor in series with the 6C4 filament and I'm curious whether a 6.8 volt 5 watt zener in series might not work and be a simple solution.

In some older GE tube manuals, mine is a 64 printing, there are charts in the very front of the book which show all the possible tubes of a certain style such as low mu triodes, grouped by filament current.

I wouldn't ever go to the trouble of rewinding the vibrator transformer, since it's not difficult to find good ones from otherwise worthless 12 volt radios from the later era which will drop right in place, that's what I've always done.


Experience is what you gain when the results aren't what you were expecting.

 Post subject: Re: Tube Cross Reference List 6/12 Volt
PostPosted: Sep Tue 21, 2021 4:36 pm 
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Joined: Feb Sun 01, 2009 2:56 pm
Posts: 12747
Location: Victoria, Australia
I note at least one "universal" car radio here that was made for 6 &12V. The radio part was the same for a considerable time. The difference was in the power supplies & several of the 6V tubes for 12V were paired in series.


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