[R-390] R-390 mods and weak points

[Robert Newberry]

Gents,

Thanks for the info it's being printed off for when I start the build up. I
also found a .pdf called the R-390 cookbook.

I'll try to research switching the 6802 to solid state.

I got a good little punch list going. I'm also documenting everything with
pictures and video.
On Dec 8, 2012 1:55 PM, "Roger Ruszkowski" <flowertime01 at wmconnect.com>
wrote:

>
> Fellows,
>
> Robert ask about R390 problems and David KW4DH pointed out the 47 ohm
> resistors in the
> power supply.
>
> There are also 4 of these resistors in the Audio deck that balance the
> voltage regulator
> current through the tube sections. Take a look at these also. One or more
> may be
> out of range from past tubes going bad and pulling a resistor into it's
> char zone.
>
> I do not know if there is room in the audio deck to install the 5w ceramic
> composition resistors.
> But I would consider it.
>
> Most of the heat from the Audio deck voltage regulators comes from the
> 6082 filaments
> 25.2 volts at .6 amps is 15 watts for each tube.
> 285 volts regulated down to 180 volts at 200 ma is 21 watts in regulation.
> That 51 watts on the audio module.
>
> You could use 4 each 5 watt resistors 1.5 K resistors. Looking to drop 75
> volts
> at 200 ma across a parallel resistance of 375 ohms 15 watts over a 20 watt
> set of resistors.
>
> Then you are looking to regulate 210 volts to 180 volts at 200 ma with
> some solid state
> transistors at 6 watts.
>
> The 26Z5 filaments were putting out 7.56 watts. The 1.5 K resistors could
> be mounted in the
> 26Z5 sockets to move the heat back over to the power supply.
>
> Once you are only trying to regulate 6 - 10 watts, solid state regulation
> with some
> plug in modules in place of the 6082's becomes real doable.
>
> Just moving over to solid state from the 6082's saves 30 watts under the
> audio deck.
> just on the filament power. You can then move some more of the regulation
> voltage drop power over to
> some fixed resistors.
>
> Several of the Fellows have presented working solutions here on the
> reflector and have
> web pages on the subject of running the R390 cooler.
>
> There are mods you plug into the 6082 sockets and save 30 watts right off
> the getgo.
>
> Roger
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