[R-390] Ultimate heresy answered

[Perry Sandeen]

Wrote: The ultimate heresy? Has anyone attempted to completely rebuild the modules or (entire?)
R390 A radio with new low noise resistors, modern caps, wiring, etc.

     Wrote: I to would like to know if anyone has done this, also add to the list the trusty
R388/URR.

Mike & Ken; the short answer is kind of.  

I’ve been "hotroding" receivers for 50 years.  I started with a S20R.  I’ve done a ARR-15, several
SP-600’s as well as some R390’s back in ‘65-‘66 at Karamursel Air Station in Turkey.

     It is good science to replace all resistors and caps.  The low noise metal film units are far
quieter that any carbon comp type ever was, could be, or will be.  Modern insulation  materials
make the same true for capacitors. Teflon sub-miniature co-ax is manna from heaven if you need to
fix any receiver co-ax problems.  The 6DC6 can be replaced with a 7788 if you want to put in a
9pin socket, re-bias and fiddle with the AGC.  This was the front end tube that we used at
Hallicrafters in the late 60’s in special OTH receivers.

     All BA’s receivers will benefit from inrush current protected electronically regulated power
supplies.  This especially true of the R-388 and SP-600  which use PS’s to develop negative bias
voltages and were designed for a lower nominal line voltage than most of have today.  The noise
filters on both the SP-600 and R-390 should both be replace with modern low leakage units to avoid
shock hazards.  R-338’s can have much better audio.  0A2 regulator tubes can be replaced with a
six stack of TL431’s for lower noise, better stability and at less expense than using the 0A2.    

 Sadly, your post will probably show the schizophrenic traits of a few developmentally limited PC
self-appointed ludites (from the Guardians of Art Society) who only write to complain.  They will
"allow" the idea of a resistor instead of a ballast tube, a new blocking capacitor for the
mechanical filters, the Langford AGC mod, accepting "GASP" solid state rectifiers!  After that, it
is almost total denial that R-390’s can have major improvements other than a product detector. 
And God help you if you propose mods with any new holes: torches will be lighted.

     Unfortunately, these vocal few have driven off the list Dr. Jerry and Dallas Langford who
have contributed to vast improvements for the R390 and R390A in particular and other BA equipment
in general.  Between them, they may have forgotten more about BA’s than most of us now

    As soon as I can  I can get to them, my three R390A’s, my three SP 600’s and three R388’s will
all work much better than when the rolled off the assembly line due to replaced components and
reworked circuits.  I have a Fluke 6080 signal generator, 200 MHz scope, audio distortion analyze,
audio power meter, and VTVM’s  to calibrate and verify what I have improved. 

     After stage one it’s off to dual gate fet’s for the IF, SS temp regulated ovens and LMxxx
series solid state audio outputs.

Bon Voyage,  Perrier




		
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