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

JVHRoberts at aol.com JVHRoberts at aol.com
Sat Oct 29 13:33:37 EDT 2005

Yes, the first two digits are heater voltage ONLY. 
And there ARE tubes that can produce enough power in the output stage, but  
NOT without a transformer! 
As far as wattage goes, Ohm's law to some extent is at work here. If you  
only have a few mA, you'll need LOTS of voltage to deliver the wattage. Besides,  
tubes LOVE voltage. That's where they work the best. 
It would be interesting to take a modern DVM through a tube Corvair radio  
chassis and measure plate and grid voltages, since that's where the voltage  
really is. I do recall seeing a '61 radio, and it had a tiny little vibrator,  
looked like a capacitor.... Needed a stethoscope to hear the whine...
In a message dated 10/29/2005 12:34:34 P.M. Eastern Standard Time,  
corvairduval at cox.net writes:

_JVHRoberts at aol.com_ (mailto: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/ Philco.

Tony, feel free to  step in here.

Frank DuVal


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