[R-390] R-390 mods and weak points
Roger Ruszkowski
flowertime01 at wmconnect.com
Sat Dec 8 13:55:16 EST 2012
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
More information about the R-390
mailing list