24 Feb
2010
24 Feb
'10
6:07 a.m.
On 24 Feb 2010 at 0:34, Dave McGuire wrote:
I remember a code-practice oscillator circuit that was line-powered a
long time ago. It used a 6SL7 twin triode, with one section
operating as a rectifier and the other, as the oscillator. The
curious thing was that the filament of the 6SL7 was powered off of
line voltage connected through a 1 uF non-polarized oil-paper
capacitor. I actually built one--it worked just fine, particularly
if you took care to ensure that the chassis wasn't live.
It may have come out of an old receiving tube manual or ARRL
handbook; I don't recall--and I hope I have the details correct.
Someone will doubtless turn up that it used a 6SQ7 or 6X8 or some
such variation.
--Chuck
Power
consumption and heat dissipation are reduced compared to a
solution using only R, and a power resistor is not needed. I haven't
tested the circuit over many on/off cycles though, to find out
whether perhaps the peak in-rush current reduces LED life.
Wow...that's pretty impressive work! Elegant in its simplicity.