[R-390] R-392 help

[Mark Huss]

Sounds like a cold solder joint.  The business I work for manufactures 
electronics boxes for the military.  When Dave pulled the case off to 
look inside, we all went 'EEEUUU...' at the solder joints.  Don't know 
what the Mil-Spec was back then, but it never should have made it past 
the Inspector with all that rosen still on the joints.

Right now, I am powering it from an open-frame Linear Power Supply brick 
rated for 28V at 4A, left over from the C-17 Simulator Program and floating 
around the back of more than a few cabinets for the last 15 years.  Too 
valueable to throw away, but never quite needed.  The surge current 
triggers the current limit (surge is about 8 amps).  But it pulls about 
2.3 to 2.8 amps depending on the position of the lamp switch and the 
ovens.  Gets up to a toasty 30 degrees C above ambient. (about 55C.).  
Well within rating, but don't touch it.  When I order the UG-77 audio 
connectors from Fair, I'll also order a 25.2 Volt 11A transformer to 
feed the filaments.  Then use an ST LM317 and a 28 Volt transformer to 
supply 30-35 Volts to the B+.  Looking at the schematic, I don't see 
anything the higher B+ should hurt.  And it should provide a bit more 
dynamic range.
Does that sound about right?

John Seboldt K0JD wrote:

> Hey, the R-392 is the only reason I'm on this list :-) ... I was 
> always interested in the R-390 family, but the R-392 showed up cheap. 
> And, as others have said, it seems to have less to go wrong with it, 
> probably being a vehicular rig.
>
> You definitely want to run it at about 24.5 volts for filament life, 
> according to a source I heard from when I first got it - makes sense. 
> I had the same experience you did, where a little switch exercise got 
> it back to life. I do have one nice quirk - the thing can go dead, but 
> tapping the chassis near one of the top deck tubes brings it right 
> back. Haven't dug inside to find the problem, since it's so easy to 
> pop the thing out and tap... the time may come when I will have to, 
> though.
>
> Nice sound with the wide LC filter bandwidths... someday may try 
> tapping the IF into something external, but it has a nice feel to it 
> just the way it is. Certainly not a rig for a crowded band!
>
> John K0JD
> Milwaukee, WI
> www.seboldt.net/k0jd
>
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