On Fri, 21 Jul 2006, AndyS wrote:

Andy writes:

I have been thinking about building a high voltage power supply
for a big amp, and am toying with the idea of using a couple of
microwave oven transformers, which I have on hand.

I plan to use two, with the primaries connected in parallel but
opposing, so that each one will supply voltage, half-wave, to a
diode ring. By doing this, I can have each core grounded like it
is used in the ovens....

So, has anyone else done this and run into any problems that
I may not have forseen ?

Thanks,
Andy


I'm in the process of building a pair of 813s (GG) with microwave oven
transformers. I have two of them, slightly different size and about 4%
difference in secondary voltage for 115 primary. Both ovens had nameplate
current specs of 15 amps, max, but the transformers look like intermittent
duty. From the schematics on both ovens, the transformers had one side of
HV sec grounded, so I'm going to use each transformer for half of each
cycle into its own diode string. Then, a bunch of electrolytics in series
with voltage divider/bleeders on each cap. I've actually had the half wave
version going, putting out 1500 vdc onto the plates of the 813s, and the
transformer I used did not hum at all (I had a variac on the primary and
cranked up from zero and back down to zero). I don't know about the
"magnetic shunt" that some of the other posters are talking about.

The schematics both showed the magnetron as in a circuit where it looked
like the tube was conducting only on one half of each cycle (no diode
rectifier, no filter caps). The filament circuit (filament winding was
separate, and apparently only a few volts and maybe tenish or so amps
judigin by the wire gauge). Stampings on one of the transformers makes it
look like it has max 2.6 kv output, so I'll need to keep primary voltage
lower to keep rectified DC output around 2400 v for the 813s.