[Boatanchors] Boatanchors Digest, Vol 80, Issue 25

[Drew P.]

Michael Baker wrote:

[snipped]

"Power transformers are not as common as they once were but, they can be had
with a bit of scrounging for reasonable $$, or NEW if you have the $$$ (See
Hammond Manufacturing, they make lots of they for the music industry and
replacement use: Antique Electronic Parts, Mesa AZ carries them along with
lots of other goodies for the "fire fet" enthusiast.  ;>)
Push comes to shove, you can always hook up a few filament transformers in
reverse mode: IE: 120-12 then 12-120 or to two of them so you get 240AC. In
FWB that comes out to 120AC=168VDC, 240AC=336VDC. More if you use voltage
doublers."

Another good transformer is a control transformer having two 220v windings and two 110V windings. These are quite common and can often be had for no cost in salvage from junked machine tools such as lathes or milling machines. Parallel the 110V windings and use for a 110V primary.  Series the 220V windings and rectify with full wave bridge and capacitive input filter for about 600VDC out.

When the HV filter choke in my Hallicrafters HT-9 shorted, taking out the power transformer with it, I put together a power supply unit that bolted in place of the defunct transformer.  Constructed on a piece of wood, it used a 100VA control transformer.  I paralleled the 110V windings to use as a primary, and seriesed the 220V windings and rectified/filtered with a voltage doubler.  It nicely provided 1200V for the 814 final tube.  No extra chassis holes were required.  It was to be a "temporary fix" to keep me going until I located a suitable transformer and filter choke.  "Temporary" has been going strong for 14 years now.

Drew