[R-390] R-392 Power Supply

[Mark Huss]

Finally satisfied with my R-392 Power supply.  At first used a 28VDC, 4A 
supply that was handy, but it went into current limit when starting, and 
got too hot for my taste.  I ordered two transformers, an LM317-based 
regulator kit, an 8Amp bridge rectifier, and heat sinks.  Wired a 120 to 
25VCT, 8 amp transformer to the 8 amp rectifier and used this to supply 
the filament current (J103-pin D).  It only pulls about 2 amps normally, 
but pulls 8 amps for about ten seconds as the filaments heat up.  
Heat-sink the rectifier.  A second transformer 120 to 28V at 1.5 amps, 
supplies the LM317 Regulator kit.  this supplies 32-33 VDC to the B+ 
input (J103-pin A).  Added 100pF caps across all rectifier diodes to get 
rid of a little hash from turn-on spikes.  Runs much cooler now.  
Before, the heat-sinks were setting at about 50C, now the rectifier heat 
sink is the hottest at 34C, the LM317 heat sink (admittedly large, since 
that is what I had) sits at 31C.  It is disapatting only 2.5 watts peak, 
and about 2 Watts average.   Switching between AC supply and DC 
Batteries shows no increase in noise.  If anyone wants a parts list and 
schematic, e-mail me.