15 Mar
2013
15 Mar
'13
1:09 p.m.
On 03/14/2013 03:16 PM, Tony Duell wrote:
Absolutely. There were 12V-anode valves for the frequency changer and IF
stages. These did not have 'space charge grids' normally. I came acorss
one audio driver valve that did ahve a space charge grid (12K5 or
something?) but it didn't drive the speaker direcrily. It drove a
(germanium) power transsitor.
Of course older cer radios were fully voalves (includign the sudio
output stage), but they had a vibrator and setp-up transformer to get
about 250V fro mteh car battery.
Anyone else remeember the 0XZ4 rectifier? Common is such car radios.
A low anode volatage is likely to cause
distortion at quire moderate
signal nlevels, which might be an advantage for that application.
Although there were some low-voltage space-charge tubes for automotive
use, just about every auto radio that I've ever seen that uses those
throws in the towel and uses a good old power transistor for the final
audio stage.
I recall building a code-practice oscillator that used nothing more than
a 6.2VAC filament transformer for its power supply. The tube used,
IIRC, was a 6SL7 dual triode. It did make use of an interstage
transformer for the audio feedback loop and drove a pair of
high-impedance headphones for a somewhat audible tone.
A number of UK magazies published 'experiement@ projects i nthe 1950s
that powered the vlave heaters from a mains transformer but got the anode
votlage my half-wave rectifying the mains -- no isolation. And soem fo
those projects used headphoens. A little bit of isulation breakdown and
you could find you'd made a very effective electric chair...
Generally speaking, however, it makes design a lot easier if you employ
a real high-voltage plate supply.
Sure. It's not hard to do.
-tony