Microwave ovens are certainly a great salvage opportunity. I have done
several sucessful low voltage rewinds/modifications to the UK 240V 600W
variety of transformer. For reduced voltage the hv secondary wire can be
scraped and solder tapped if the winding edge is sufficiently open. (Care
required to avoid shorted layers and liberal use of silicon rubber on the
joint ) But it should be noted that the voltage load regulation is poor.
Definitely a problem in ssb plate applications. Various suggestions to
alleviate this, including a center tapped pair of transformers in a full
wave bridge, have been published in the UK Radio Communication over the last
decade.
Peter
----- Original Message -----
From: Bob Duckworth <wb4mnf@atl.org>
To: <amps@contesting.com>
Sent: Wednesday, August 16, 2000 10:14 AM
Subject: [AMPS] Bargain basement broadband tetrode amp question(s)...dead
horse??
>
> Forgive me if this has been beat to death already...
>
> I have been resurrecting a number of 30's vintage radio receivers lately.
> Hallicrafters SX-18, National NC-44 and NC-46, etc.
>
> I notice that they all use a tetrode for audio output stage. 6F6 in the
> SX-18.
>
> Circuit is cathode biased, grid driven, and output is by transformer
> between the screen and the plate.
>
> Very simple circuit.
> One resistor for cathode bias.
> Bypass cap for cathode (audio freq, 10mfd or so)
> Output transformer.
>
> Is the same circuit good for a broad band RF amp?
> Transmission line tranny for output. Perhaps an extra
> winding for degenerative feedback.
>
> I'm thinking bargain basement amp here. 813 tube
> microwave oven transformer, transmission line wound
> on surplus toroids.
>
> -bob
>
>
>
> --
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>
>
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