13 Jun
2002
13 Jun
'02
6:09 p.m.
Tony Duell wrote:
Anyway, what amazed and worried me was the power
supply circuit used. It
consisted of a 6V transformer for the valve heaters and a half-wave
rectifier to produce the HT (B+) directly from the mains. The neutral
line of the mains was connected to the metal chassis. And some of the
projects used headphones. I can think of plenty of ways that could turn
into an 'electric chair'....
Sadly this seems to be the norm for some Valve projects. I have old book
"Electricity and Electronics " - McGraw Hill 1964 that has a One Tube
Radio with a 1/2 wave recifier (110 AC) and 25 watt 750 ohm resistor
to drop the AC to 12 volts for the heater. All the projects use a audio
output transformer so the speaker is the only safe item.
--
Ben Franchuk - Dawn * 12/24 bit cpu *
www.jetnet.ab.ca/users/bfranchuk/index.html