[R-390] R-390 Problems Update

[David C. Hallam]

I replaced the 6BA6's in the VFO and BFO with 12BA6's, which eliminates the
need for the resistor to replace the ballast tube.

There has been a recent discussion on this list about the ballast tube and
ways to replace it.  I think the general consensus is that the ballast tube
really is not needed to stabilize the VFO unless you looking for the last
little bit of stability.  If so, you need to replace the ballast tube with
something more sophisticated as given the relative "stability" of the AC
line, the ballast tube doesn't do much in that regard.

Replacing the VFO and BFO with 12 V filament tubes is one of the suggested
mods.

David

-----Original Message-----
From: JamesMiller [mailto:jmiller1706 at cfl.rr.com]
Sent: Sunday, October 31, 2004 9:15 AM
To: dhallam at rapidsys.com
Subject: Re: [R-390] R-390 Problems Update

With just a paper clip jumper you may be putting too much voltage on the BFO
and VFO tube filaments.  A 22 ohm (5-10W) resistor is preferred, or another
mod inolves using a 12BA6 tube in the ballast socket (there is a mod for
this published on the web).

----- Original Message -----
From: "David C. Hallam" <dhallam at rapidsys.com>
To: "R-390 List" <r-390 at mailman.qth.net>
Sent: Sunday, October 31, 2004 8:02 AM
Subject: [R-390] R-390 Problems Update


Thanks to all who replied to my request for help.  The problem turned out to
be a failed ballast tube. I changed the VFO and BFO tubes to 12BA6's and
stuck the paper clip jumper in the ballast tube socket.  All is working well
again.

I don't know if the failure of one of the 26Z5W rectifier tubes precipitated
the failure of the ballast tube or if they were two unrelated malfunctions.
The rectifiers were replaced with a pair of Ted Weber's copper top silicon
plug in's.

David C. Hallam
KC2JD


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