new hamfest finds

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sun Jun 6 12:23:55 2004

> I remember, also as a kid, so mid to late 70's, pulling apart an old valve
> radio I picked up at a jumble sale. Battery operated, with spaces for
> about three different sort of huge batteries... I think one of those was
> supposed to be an HV battery - I never came across one though.

Most valve portables used 2 batteries -- HT (almost always a dry battery,
between 67.5 and 150V) and LT (originally a wet cell accumulator, later
radios (1950s) used a dry cell pack for this too). Grid bias was almost
always provided by 'self bias' circuits (resistors in the cathode circuit
of the valves, etc), but some early sets used a 9V (tapped every 1.5V)
grid bias battery.

I can just rememebr using the 90V HT batteries (Every Ready B126 IIRC).
The LT batteries often had ADnn numbers, the AD stood for 'All Dry'
refering to the fact that you didn't have a wet cell in the radio.

I also remember reading about an RCA (I think) set that was valved but
ran off a single wet cell. It used a vibrator and transformer to get the
HT.

These days, if you want ot use such a radio (and they sound a lot better
than many modern sets, and yes, some of them did cover the FM band) you
either use 10 PP3 (9V) batteries in series for the HT or a mains PSU. A
30V (RMS) trnasformer followed by a votlage doubler rectifier works fine
for most sets.

-tony
Received on Sun Jun 06 2004 - 12:23:55 BST