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

Tony Underwood tonyu at roava.net
Sun Oct 30 00:38:43 EDT 2005

At 11:36 hours 10/29/2005, JVHRoberts at aol.com wrote:
>OK, SOMETIMES my memory and the facts do get confused. I found a 1960
>Corvair radio in my heap, looked at it CAREFULLY. It would appear 
>you are right.
>Still, I remember a vibrator in that 1961 radio from years gone by...

The radio wasn't a Delco, must have been something else.   The 
vibrator wasn't necessary for anything running space charge tubes 
since their plate/screen voltage was 12 volts straight from the 
battery.   The output was a germanium transistor, class-A and 
transformer/autoformer coupled straight through to the speaker since 
the big "broad-chip" output transistor had a low impedance which 
matched up to the speaker reasonably well, with the auto-transformer 
being along to do waveforming duty.   So, space charge tubes were 
used to do RF/IF work and low level audio, and the big germanium 
transistor drove the speaker.   GM used those big germanium 
transistors up through the '70s for audio outputs in most Delco 
radios, as did Bendix, Philco, Motorola etc although the others 
started using silicon transistor outputs before Delco switched to ICs 
as audio outputs.

But many 12 volt car radios in the late '50s up through the early 
'60s were using space charge tubes with that Germanium single-ended 
class-A output.    It all made for a more compact radio that also 
didn't use as much current from the battery as the older 6 volt 
vibrator radios which, in the "glory days", used a batch of octal 
style tubes with 6 volt filaments that on average would use around 
600ma of filament current per tube.   With 7-8 tubes in the radio, 
this added up quick.   Then of course there was the B voltage supply, 
with the vibrator stepping 6 volts up to around 350 or so to run 
audio outputs (generally 6W6 or 6V6 tubes, sometimes a pair in 
push-pull in the better quality radios which meant you could get as 
much as 15-20 watts or more of power out of those old radios.

However, you couldn't listen to them for long with the  engine not 
running.   Some of them used 20 amps or more of power just by being 
turned on.  Crank the volume up and they drew a bit more.   They 
helped heat the car in winter...;)

Anyone remember those days with older cars and the 6 volt radios that 
would warm the whole dashboard after running an hour?

In any event, the space charge tubes that came along in the mid-50s 
really made car radios a better proposition with smaller size, less 
current draw, and obviously less heat under the dash.   They were 
dependable as well, with the space charge design of the tubes making 
them durable for the long run with a lot of these old tube type 
radios still working today without ever having had a tube 
replaced.    There are three tube type radios in the Vairs here, all 
of which work fine and none have been apart outside the one in my '60 
4-door which had to have an emitter resistor in the output stage 
replaced when it got a dose of over-voltage when a voltage regulator 
went south and dosed the radio with who knows how many volts..  no 
filaments opened up  but it cooked the emitter resistor.   I replaced 
it, radio still works fine.   No other repairs have been done to it 
since it went together in 1960.   Delco built them tough.   Likewise 
the radios in the Lakewood and the '62 ragtop, still work fine.

By the way, the smallest car radios Delco made until the X-body car 
radios came around were the space-charge tube type radios of the early 60s.


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