[R-390] R-390 Voltage Regulator

[Flowertime01 at wmconnect.com]

Dave,

Solid stating the 6082 series regulator is not a bad idea. 
A plug in, no change to the receiver unit is very doable.

If you have ever built a simple transistor series pass voltage regulator with 
zener reference power supply you can do one for the R390.

There are three ways to deal with the heat sink for the transistor that will 
replace the 6082's.
1. Really engineer a heat sink to fit in the 6082 space.
2. Bolt a TO2 transistor to the side of the receiver with an adapter plate.
3. Use a somewhat long (2 foot) wire harness and mount the transistor on a 
heat sink out side the receiver (and maybe add its own fan).

First good thing is you will pull two each 6082s off line.
At 16 watts each of filament power the receiver is 32 watts cooler.

Second good thing you pull the voltage regulator tube 5651.

Third good thing is a zener reference and series pass type transistor 
regulator will work fine.

Fourth good thing is it can all be plugged in with no drilling or 
modification to the receiver. This is fully reversible.

Down side is about 50 watts of power dissipated from one or two transistors.
Remember operators use to fry breakfast and make coffee on these receivers.
I have found more than one can of rations heating atop a receiver.
Left it right there less I got shot for stealing someone's meal.
The R390/A just will not get up to that heat level unless you turn the 
crystal oven on.

I am going to suggest some 8 pin octal relays as the starting point.

Most relays come with plastic covers. remove the screws and discard the cover.
Heat the socket pins and unsolder the relay. Save the relay coil wire for a 
stealth antenna. You know have a base to build on.

You may not need to build two units. The 6082 are triodes and run two tubes 
four triodes in parallel A triode section of a 6082 will handle 13 watts. Two 
tubes four sections is only 52 watts. The R390 likely does not run the 6082 at 
full capability, so somewhat less than 52 watts may be needing radiated as 
heat.

A 2N3055 will do a 100 watts.

If you are not going to slide this receiver into a real tight rack spot where 
you would likely scrape a TO2 transistor off the side of the receiver frame, 
you can mount the regulating transistor to the receiver main chassis. Heat 
sink and large surface area are key here. Plan the large TO2 style transistor to 
mount over one of the chassis vent holes along the side rail. Use a socket for 
the TO2 type transistor regulator.
Plan a large sheet of metal that will lap over a couple vent holes so you can 
run some hardware through these holes to hold the new heat sink plate to the 
chassis.

You can hang heat sinks off the 8 pin relay sockets. We will have to do the 
math on an R390 B+ line for the real current and the real voltage that is 
dropped. Someone on line here will have that information at hand. Running two 
transistors on two heat sinks on two sockets plugged into two 6082 sockets will 
want to be referenced to the same base reference voltage. You can plan a wire 
between the two plug in units
rather than rework the chassis. Remember the goal is a plug in and easily 
reversible modification. Once we look at the number of watts we need to radiate 
as heat, we can consider how large the heat sinks would need to be and not be 
an operating problem. Remember the 6082 have been putting that heat out for 
years plus the filament heat. When this change goes in the receiver will still be 
running 32 watts cooler than the factory stock tubes.

Now you have a 100 watt TO2 type transistor bolted to the side of the 
receiver with plenty of heat sink. You plan to dissipate not more than 50 watts from 
it. Do not worry that you covered 3 vent holes, as you took 32 watts off line 
and are going to move another 50 watts to the out side of the chassis.

Plan on using two relay 8 pin octal sockets. Rather than play with the 47 ohm 
resistors under the chassis, solder a wire into the socket pins for each 6082 
cathode (a total of four wires) and each plate (another four wires). The 
cathode wires of course go to the emitter of the regulator TO2 type transistor 
(2N3055 or something comparable) and the plate wires go to the collector of the 
transistor. This will draw the current through all 4 of the 47 ohm resistors. 
This also keeps the current spread over all the tube socket pins. Rather than 
pass the full current through any one socket pin, keep the power spread out. 
Your new plug in wiring may take the load, but consider all the original wiring 
under the deck. Its so much easier to just build a mod that will work and play 
well with a little prior planing than to rewire a burned chassis.

The next operation is to build up a suitable reference voltage. The 5651 is 
only 85 volts. The solid state regulator wants a reference .6 volts above the 
desired B+ voltage. My choice would be for a couple 5 watt zener diodes in 
series with a proper filter cap across the zener diodes and a voltage dropping 
resistor between the high power supply voltage and the junction of the regulating 
transistor base and zener reference.

You could get complex and zener part of the voltage, then use a dropping 
resistor between the zener and the regulating transistor base. This regulation 
would not be as stiff as a full zener voltage.The 5651 reference voltage on the 
6082 grid pins has its own dropping resistor under the subchassis. Using it for 
the reference may be more complex than just installing some thing new. 
Considering today's power line stability (you were not planing to use this receiver 
for field day were you ?) you could likely use no reference zener at all. A 
little voltage measurement on the receiver as is, and some math, you could 
likely  determine a 1 watt voltage drop (use 2 watt resistors) between unregulated 
B+ (what ever is on the 6082 socket for the plate pins) and ground. The low 
transistor base current compared to the resistor current at 1 watt between B+ 
and ground may be more than good for the application. Some where will be two 
resistors that provide a voltage division that would serve as the reference 
voltage.

I think this calls for an engineering evaluation and poll. What say yea all?

Find ground on one side of the tube filaments. The reference voltage diodes, 
resistor, and capacitance could all be mounted on the octal sockets. Depending 
on heat sink preference, and the regulating transistor, every thing can be 
mounted on the relay octal sockets and plugged in. Or a wire harness can be 
formed between the relay octal sockets and the regulating transistor mounted on 
the heat sink. The heat sink may be mounted either on the chassis, or as a whole 
separate unit on an extended wire harness.

Some where someone has done this already. Watch for some more mail here from 
the group. Some where someone knows exactly what value parts to be hunting up 
for this change.

Go for it and get that receiver operational.

Roger L. Ruszkowski KC6TRU