[R-390] R-390A Current Regulator Tube replacement?

[David C. Hallam]

I guess I have to ask why?

Tests run by Dallas Lankford and published to this group showed the resistor
substitution was just as effective as the ballast tube and maybe even
better.  I also think he stated that his test showed if you really wanted
stability, the VFO and PTO should be run from a separate regulated DC
supply.

Either replacing the ballast tube with a resistor or replacing the 6BA6's
with 12BA6's and the ballast tube with a short is effective and reversible
with a few minutes work not involving circuit changes.

David
KC2JD

-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of Dan Rae
Sent: Monday, December 05, 2005 6:01 PM
To: R-390 at mailman.qth.net
Subject: [R-390] R-390A Current Regulator Tube replacement?


One alternative I don't remember seeing for losing the hard to find
ballast tube is to run the two oscillator tube filaments from the
otherwise unused 12.6 Volt center tap on the power transformer.

This involves adding one wire in the power supply (from transformer pin
9, the centre tap,  to the previously unused pin 9 on the connector
J111), moving the filament feed to the IF strip from the present pin 1
inside plug P111 to pin 9 (in mine, it's the thinner of the two white /
brown wires), and finally shorting out the current regulator pins 2 and
7 in the IF strip.   And that's it.

This has some advantages over the methods using a resistor, it's cheap,
retains the original tubes rather than replacing them with 12BA6s, but
does not have the advantages of another form of current regulator, solid
state, for example.

Anybody tried this before, or got any comments for or against?
73
Dan
ac6ao / g3ncr




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