28 Feb
2010
28 Feb
'10
7:42 p.m.
Tony Duell wrote:
They were on occasion, but more so in black and white TVs. TMU, the greater B+
I was thinking of monochrome TVs...
On Fri,
Feb 26, 2010 at 2:26 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
I am suprised that voltage doubler PSUs (2 diodes, 2 capacitors) weren't
used in the States. Ah, TV sets over here rarely had power
transformers at all... Every valved
monochrome TV Iv'e worked on... had a 300mA series string of valve heaters
and got the B+ line by half-wave rectifying the mains.
Sure, but your mains were twice the voltage of our mains. current requirements or quality expectations tended to
rule them out for colour TVs.
In other instances of novel fulfilment of power supply requirements there were
really weird structures such as feeding another functional unit (some sync
processing say) from the otherwise-wasted energy in the class-A audio output
cathode bias resistor.
Ah yes, I seem to remember readint that was known as the 'stacked B+'
circuit.. You got some verry odd effects if the decoupling capacitor went
open-circuit...
At least one Philips tape recorder (I thick it was the 'upright' model
EL3514) used the bias voltage for the output pentode (which was used as
the bias/erase oscillator in record mode) as the filament supply for a
sub-miniature indicator valve (magic eye) -- I think it was a DM71 --
used to show the recording level.
-tony