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In Reply to: RE: Mikey Helps The Technically Challenged - Me. posted by 6bq5 on October 14, 2014 at 15:23:01
While it is work, recovery from a failed power transformer in Scott 299Cs, 299Ds, LK72As, and LK72Bs need not be hideously expensive. The "beefed up" replacement power trafo Triode Electronics sells for Dyna ST70s can be adapted to the need.
Use 1 of the 2X 6.3 VAC windings to energize the 6 power section tubes. Voltage double, with Schottky diodes, the other 6.3 VAC winding and 7812 regulate the resulting DC, providing for the 4X 12AX7 heaters. Half wave rectify the bias tap (a Schottky diode is preferred) and CRC filter the resulting "raw" DC to obtain the C- supply.
The scheme outlined above is made possible by the fact that the heater current draw of a 7591 is less than that of an EL34. :>D
Eli D.
Follow Ups:
As always, you are a fountain of information, Eli. Is there anything that works with a Scott 222D?
Dave
Contact Heyboer. You may have to send the failed item in. Unfortunately, I am unaware of a suitable off the shelf power transformer.
Eli D.
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