[R-390] Help with R-392

[Drew Papanek]

On Ronnie Davis powering his R-392, Bruce Ussery wrote:

>For what it's worth, 3 amps sounds like about the right current draw. Both
>of mine draw about 2.6 amps; one fluctuates between 2.6 and 3 as the
>calibrator crystal oven cycles (I assume).

Reduction of internal temperature is of benefit to extend the components' 
lifetime.  If 3 amps continuous there is nearly 90 watts in the (sealed) 
box.

It sounds like the calibrator crystal oven draws about 400 mA. Additionally, 
the audio output tube heater adds about 15 watts of heat with its 625 mA 
heater current drain.

Elimination of these loads would reduce total receiver consumption to 2 amps 
(easier on the power supply) and eliminate 15 to 28 watts of internal heat.

With the 6.3v calibrator crystal oven disconnected, my R-390A has no problem 
with calibrator frequency stability.
That may also apply to the R-392. The constant (high) temperature provided 
by the oven is of use when operating the radio in Antarctica-hardly the type 
of service most of our radios see.

The filament heat of the audio outputube can be eliminated by a solid state 
repacement (blasphemy). Rovero's R-392 website shows a couple of different 
schemes.

For the modification-averse, output tube could be removed and audio taken 
from one of the grids (the one driven by the cathode of the phase splitter) 
to be fed to an external audio amp/speaker.

Simplest heat reduction would be to slide the radio out of the case a bit.

>And I gave up on AC power supplies after trying three. They all radiated RF
>noise, mostly below 8 Mhz, so I got a couple of big gel cells at a hamfest
>and a "wheelchair battery charger" through the internet.

Most abundant are switch mode power supplies.  They are noted for 
compactness, high efficiency, light weight, low cost and high levels of RF 
noise.  What one needs is a linear power supply.  The attributes are the 
opposite of those listed above for SMPS's.  A simple unregulated 
transformer-rectifier-filter type supply might suffice if it has huge filter 
caps for low enough ripple.

Drew

"Vicariously repairing and modifying R-390x via advice to others"

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