[R-390] RT301 current regulator tube

[David Wise]

Listening to AFRTS on SSB, I saw enough frequency bending to annoy, with a receiver equipped with 3TF7 and inrush current limiter.  Delta-I as the 17MHz oven cycled caused the power transformer primary to jump several volts, and the 3TF7 was slow to react.  I have not measured frequency drift since then - my 3DW7 keeps the heaters steady to the limit of my ability to measure.  ISTR that heater caused more drift than B+.

My house AC mains also jump several volts randomly several times an hour.  Lots of load clicking on and off on my pole pig, I guess.

Dave Wise
SWL in Hillsboro Oregon (inactive)

Funny that one of my replies shows up full of MIME decorations; I have Format set to Plain Text.

-----Original Message-----
From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On Behalf Of Jacques Fortin
Sent: Friday, December 31, 2021 11:53 AM
To: 'Jordan Arndt' <Outposter30 at shaw.ca>
Cc: 'R390A' <r-390 at mailman.qth.net>
Subject: Re: [R-390] RT301 current regulator tube

Hi all,
I just found the V-I plot I made in 1984 from the 2HTF11B that came with my R390/URR when I found it.
For the record, the Amperite 2HTF11B is a functional equivalent of the 3TF7.
And for the sceptic ones, look at the TM 11-856, page 12, figure 11.
At that time, it was right on the 300mA target between 10 and 18V.
I will attach the pdf, but not sure it will "pass".

And about beating that dead horse: Dallas Lankford already published in 2004 that the best BFO + PTO stability was obtained by powering the filaments with a voltage regulator (he used a 7812, I believe).

73, Jacques, VE2JFE in Montreal