[R-390] RE: Help with R-392

[James A. (Andy) Moorer]

----- Original Message ----- 
>
> If I recall correctly, the R-392 has 2 input pins for the 28 volt source;
> one supplies the heaters and t'other supplies B+. (If I recall
incorrectly,
> maybe it could be made so with minimumodification).
>
> Some have reported improved performance by upping B+ to 35v or so while
> leaving filaments at 24v.  If one were to go that dual power supply route,
a
> low quality 24v supply (maybe even AC?) could heat the filaments and a
well
> filtered supply at higher voltage could provide B+.
>

The filament current is about 1.5 A and the plate current is about .5 A.
They don't need to be regulated, but any 60 Hz hum will go right into the
audio. At startup, the filaments will pull up to 5A or so for a few tens of
milliseconds - long enough to blow any normal fuse.

I fiddled around with separating the filament and plate voltages. My
conclusion is that you really shouldn't set the plate voltage over about 32
volts. It starts sounding rough and distorted above that. I pretty much
ended up setting it at 30 volts and leaving it.

One thing I haven't seen discussed much is the filament voltage. The radio
ran on 28 volts, but most of the tubes are rated for 26 volts. They also
have two 12.6V tubes in series for 25.2V. I think 28V is too high. I set the
filament voltage down to 26 volts on mine. I don't notice any difference in
performance.

Enjoy!

James A. (Andy) Moorer
www.jamminpower.com