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