1 Mar
2010
1 Mar
'10
11:41 a.m.
Tony Duell wrote:
Doublers often were used in transformerless sets in the US, perhaps
almost always. ISTR seleniums with a gradual migration to solid state
Right. I am not suprised.
I have never seen the service manual or scheamtic for a valved US TV set.
Unlike radio sets (the AM broadcast band is pretty much the same in the
US and Europe, and if oyu want to recieve the European 'long wave' band,
it's a simple modification), the differnce in TV standards meant that
almost no US TVs ended up over here.
Wit hradios, the difference in mains voltage was often handled by an
aditional dropping resistor. This was commonly something called a 'line
cord' which was a piece of 2 core cable with one wire being resistance
wire (!). Needless to say shortening this (which some owners did for
neatness) was a bad idea... This line cord also ran hot, if left coiled up
it was afavourite plae for cats to sleep :-)
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.
-tony
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. diodes as they became available in the needed voltage
ratings. At the
moment, I can't recall having seen vacuum tube diodes used in a TV
Mopstof the UK monochrome vavled TVs I've worked on ued either a selenium
('metal' ) rectivfier or a silicon diode (BY127 or similar). There were
valve rectifiers (PY31, PY82), but they are much less common. Of course
our sets just used a simple half-wave rectifier from the 240V or so mains.
doubler, though I imagine there were instances of
that. I still have a
little 14" B&W Motorola in the garage (with a bad CRT) that might not
have the doubler. If I ever find it again or the Sams for it I'll have
to check and see. Please keep in mind that I'm speaking from my
memories of TV repair in about the 1956 to 1960 area. Once I completed
college in 1960 my path led me to devices mostly containing those
mysterious devices with no filaments. :-)
And now we have TVs with no filaments at all. LCD panels with CCFL
backlightes or plasma panes. I am not looking forward to having to repair
one of those things. BGA chips, etc. and yes, according to the service
manual foe the set we hae, you do do component-levle repair...
-tony