<VV> Re: Was Pertronix, Now Space Charged Tubes

Frank DuVal corvairduval at cox.net
Sat Oct 29 12:34:19 EDT 2005

JVHRoberts at aol.com wrote:

> Keep in mind those first two digits refers ONLY to the filament heater 
> voltage. ALL stock tube radios for cars still had vibrators, and still 
> needed MUCH higher than 12 volts to the plates and cathodes to work 
> properly.
> The reason some used a transistor output was cost. It eliminated the 
> need for a relatively expensive output transformer, since tubes are 
> high impedance and transistors handily drive low impedance loads with 
> significant power from 12 volts.
> So, inside of that 'space age' radio, are still some pretty good 
> voltages, usually over 100 volts.

In a word, NO.  Check the RCA Receiving Tube Manual and you will see the 
following tubes were made with plate voltages of 12.6 volts.  Cathodes 
in car radios run near 0.0 volts. :
12AC6, 12AD6, 12AE6, 12AE7, 12AF6, 12AJ6, 12AL8, 12BL6, 12CN5, 12CX6, 
12DE8, 12DL8, 12DS7, 12DU7, 12DY8, 12DZ6, 12EA8, 12EC8, 12EG6, 12EK6, 
12EL6, 12EM6, 12F8, 12FK6, 12FM6, 12FR8, 12FX8, 12GA6, 12J8, 12U7.

None of these could produce power for audio output stage. Most run 1 or 
2 mA plate current. One was rated at 35 mA, but that is less than a 1/2 
watt. You will not see a vibrator in a Delco Corvair radio, but you will 
see tubes in 1960, 1961, and 1962. No hidden batteries, no multivibrator 
circuits to feed step up transformers. No "high" voltage. The other car 
lines were also using Space Charged tubes in the early 60's, like Ford/ 

Tony, feel free to step in here.

Frank DuVal

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