[R-390] RT301 current regulator tube

[Jim Whartenby]

No need to rectify and filter.  If you want to go the LM317 rout, all you will need is to add a bridge rectifier to the current regulator circuit.  The AC leads go to the appropriate pins of the RT-301 socket and the +/- leads go to the LM317 appropriate connections.  No matter what part of the AC cycle, the LM317 will always see the correct polarity and limit the current to the set value.  I just checked the circuit at  https://www.bristolwatch.com/ccs/LM317.htm   and see no need for a ground connection, but since I haven't tried that particular circuit, a ground connection for the bypass cap might be prudent for stability.
But if you go from a 6 volt heater to 12 volt heater oscillator tubes, you can save a few watts of actual heat in either flavor of R-390 by eliminating the current regulator all together.
HNY,Jim

-----Original Message-----
From: Jacques Fortin <jacques.f at videotron.ca>
To: 'Tisha Hayes' <tisha.hayes at gmail.com>; 'R390A' <r-390 at mailman.qth.net>
Sent: Thu, Dec 30, 2021 3:33 pm
Subject: Re: [R-390] RT301 current regulator tube

Hello Tisha,

When you mention using a LM317, is it used in Voltage regulator, or in
Current regulator configuration ?
In both cases, you will need to rectify and filter the 25.2 Volts AC supply,
then use the LM317 thereafter to supply constant 12.6V DC to the filaments
or 300mA DC, whatever.
And full-wave rectification cannot be used there, unless you modify the BFO
+ PTO filament wiring...
As the maximum voltage across the filtering capacitor will reach about 35V,
it also means that a quite substantial heatsink for the LM317 will be
needed.
Worst case, 6.72W have to be dissipated from it (in either configuration).

I prefer to use the 12BY7/12BH7 trick...

73, Jacques, VE2JFE in Montreal

______________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:R-390 at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html