Bud Wireless Phono Osc

[Brian Carling]

This sounds like a great conversion project for use on 160 or 80m CW!

On 29 Sep 99, at 1:20, Hue Miller wrote:

> Hello, pipsqueek broadcast veterans: i just traced out the wiring of a BUD
> WO-8
> Phonograph Oscillator, and here's my comments.
>
> The device uses a 117L7 tetrode - diode tube. The diode is the power
> rectifier
> and the other is the osc., with the G2 element going to the center tap of the
> tuned circuit coil between the plate and B+ ( RF ground). The coil saves money
> and space by just being wound around the ceramic holder of the mica
> compression
> trimmer. Output is by means of just some turns around the same coil, with only
> one side of this winding connected, and that goes to the antenna connection.
> Audio input is to the G1 and power ground with a 600kR load across it. This
> all fits in a perforated metal box about 1.5 x 2 x 5 ins.
>
> There's a couple points to have reservations about: the lytic cap (20+20/150)
> is right parallel to the tube - nice supply of heat to help dry it out.
>
> The shield of your audio input cable goes effectively, right to one side of
> the
> wall plug. I wouldn't use this with my CD player, or anything! this might make
> for sparks in the youngster's broadcast studio!
>
> With this minimal output coupling, probably less than 50pF equivalent to the
> antenna from the tuned circuit, i do not think any kind of antenna tuning unit
> would have been very effective. You could put another hi-impedance circuit
> from
> the ANT connection to ground, and then use that to match to the (capacitive
> reactive) antenna, but then, this becomes part of the same components that
> set the frequency of operation - that would be a challenge to tune up for
> match
> and set on frequency at the same time.
>
> The oscillator current and operating point is set thru a 600R resistor from
> cathode to ground. Lowering this resistor would increase the oscillator's
> power, and that's probably how that previous raconteur achieved the remarkable
> range he got - and why the tube shortly went away!
>
> Since having one side of AC power right on the ground connection doesn't
> appeal
> to me, i don't think i'll be using this one to broadcast CDs soon - I think it
> needs really to be FETized!
> Hue Miller
>
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