16 Mar
2013
16 Mar
'13
3:02 p.m.
On the subject of tube radios, I picked up an RCA
Victor BP-10 awhile
Amongst others I have a 1960s Vidor (UK) portable vavle radio. It's not
small, it's about the size of a large transitor radio. But as well as
coverign the AM broadcast bands (MW and LW over here), it also covers
band 2 FM. Not many valve portables hat that feature.
back; this is a portable from about 1940 and it's
actually pretty darn
tiny for a tube-based unit. (And it runs off a 63.5V B battery (#467)
and one D-sized 1.5V battery. Amazingly you can still buy the 63.5V
batteries new...). Anyway, I bring it up because aside from its small
If you cna't get the right battery, you can often get waway with wiring
9V PP3 (006P, wahtever) batteries in series. 7 for your little set, 7 or
8 for the UK sets that need a 67.5V battery and 10 for a 90V battery.
form factor it has one other attribute I've never
seen in a tube radio
-- it starts playing almost immediately (within a second) of turning it
on and the tubes never seem to get warm at all. All the other tube
units I've ever seen take 10-20 seconds to warm up first. Makes me
wonder a) what's special about this unit and b) why other units didn't
do the same -- seems like a pretty useful feature.
The battery-opeated valves are likely to be directly heated. That is, the
filament is the cathode. Indrectly heated valves, like those in mais
powered sets ahve a separate filamanet 9or heater) which heats the
cathode sleeve. The latter is what emits electros. Indirectly heated
vavles arte much slower to warm up [1] but you can heat them using AC. If
you do that with a directly heatewd valve you will get a lot og main hum
in the anode current.
[1] The warm-up time depends in part on the thermal condictivity between
heater ad cathode. And this is releated to the electircal isolation
between those electrodes. A vavle that can stand a high heater-cathode
votlage, like some of the rectifiers used in AC/DC sets and (even more)
some TV booster diodes 9damper diodes) will take longer to warm up than
other types.
-tony