"patrick-turner"
There is an artical posted here about tubed phase shift oscilators at : -
http://www.rfcafe.com/references/pop...lectronics.htm
Its an old 1958 article with a hell of a lot of info to digest because
unlike so many modern descriptions of anything technical, the old guys could
say a lot, and not leave out very much. I think my father's generation were
better communicators than many of today's website creators who just post a
stupid brief plagerised picture of something, then think they are God's gift
to the Universe of Information.
But I digress.
I do have a lot of 3 gang tuning caps from old radios which will never be
used for radios again, and so its possible for me to mount maybe 8 of them
in a box with so I'd get 3 caps with variable range 8 x ( 45 - 450pF ), ie,
360pF to 3,600pF.
Has anyone else built a decent phase shift oscillator with wide range of F?
** Not me.
But I do have an all valve Wien Bridge oscillator using a dual gang
condenser, taken from a 1940s radio.
Owned it since I was 15 years old.
Tube line up: 2 x Mullard 6AM6, 1 x AWV 6BQ5 & 1 x Miniwatt 6V4
rectifier.
Three ranges: 9 to 218 Hz, 185 to 2158Hz & 1889 to 21,899Hz.
Two 18 megohm resistors used in the low frequency range.
The 6AM6s are wired as triodes.
Stabilisation is by an R53 NTC vacuum bead thermistor.
The condenser is electrically isolated from the chassis and lives in a steel
box of its own for shielding.
The shaft is driven by a backlash free, 60:1 worm reduction drive and a 200
point scale.
Verrry silky.
Once warmed up, it is remarkably stable.
THD is a modest 0.2%, pure 2nd harmonic.
Gave it a major renovation about 10 years back - including MF resistors,
new tag board, all electros and many poly film caps etc.
Nostalgia is a real bitch.
.... Phil