[R-390] R-390 Digest, Vol 82, Issue 23

[Paul Galpin]

They said:

> 
> When one considers the time frame that these radios were built and
> used,  the methods of providing the the power source, and the overall
> use, the entire voltage regulation thread is pretty moot.
> 
The use of 3TF7s, 12BA6s, or the 40 to 50 Ohm @10W resistor
> is more than adequate.
> 
> This entire idea of "attempting" to regulate the filaments of the PTO
> and BFO is like suddenly deciding that you wand Solid State and Digital
> Readout precision
> 
> I really can't see what's wrong with utilizing the existing 12 volt transformer tap or the notion of inserting a plug-
> into ballast tube socket, regulator unit.
[!] 

I say "Yes, yes, and yes!"
But it's fun to do these theoretical brain exercises, think up an idea, and see what might happen as a result!

Of course, if you are trying to keep it original, then the 12V tap is out, as is the three-core mains connector.
My take is to make it safe (3-core mains lead), use a good 3TF7 if you have one, otherwise a 42R resistor is quite adequate. 2x
12BA6, or 12V tap, make unit swapping just a tad more difficult.

In my two R390As I have one original PSU, and one with a "made-to-order" transformer. 24V ac only - no 12Vac tap, and I only have 2x
12BA6s.  So I am staying with the power wastage of a 42R5W in one set and a good (0.31A) 3TF7 in the other.


Paul Galpin
ZS2PG