In message
<of237cb435.ac0c42c8-on88257992.0067506c-88257992.0068c...@selinc.com>,
dated Fri, 27 Jan 2012, don_borow...@selinc.com writes:
In the mid-1930 in the USA, there were some radios designed with 3-wire
power cords -- two copper conductors and a third resistive conductor.
This was because the heater string voltage added up to 69 volts (at 300
mA) for a typical 5-tube radio. These cords soon acquired the nickname
'curtain burners'.
This is a bit OT, but that sort of radio was exported from US to Britain
right up to the mid 1950s. There were also a few European ones with 0.2
A and 0.15 A heaters.
Other radios had a "ballast tube" (a glorified light bulb) to drop the
excess voltage (and add more heat inside the radio).
Well, that's a bit harsh; they (called 'barreters' in Britain) had an
iron filament in a hydrogen atmosphere and were quite good
constant-current devices.
Eventually UL forced the situation, and the tube line-up was redesigned
so that the heater voltages added up to 120 V (at 150 mA).
There were even tubes with 117 V heaters - rectifiers and power
pentodes. No 220 V or 230 V types, though.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
Some people who are peeling the finch of the financial crisis are thinking of
biting a rook.
-
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