[R-390] in rush current limiters

Sun, 22 Dec 2002 16:03:01 -0800

The current is 300 ma.  AC.  It is simply the filament current of two 6-volt
miniature tubes (v508-6BA6/5749, V701-6BA6/5749) in series.  The source
voltage is about 25 volts.  12 volts is taken by the two tubes in series,
and the ballast and decoupling inductors
drop the other 13 volts.

The idea is to build a 9-pin miniature tube plug-in replacement with no
modification to the R-390A.  Only two wires are fed to the ballast socket.
Ground is not available unless obtained by a tertiary wire or the socket
shield.  Heat dissipation might be the biggest challenge in a plug-in
solid-state replacement.

A very simple modification is to simply jumper the ballast pins 2 and 7 with
a simple plug-in wire jumper and replace the 6-volt tubes with their 12-volt
equivalents.  The receiver remains very stable even when the filaments are
not current regulated by the ballast tube.

Funny thing, think I put a 12AU6 in the PTO in the receiver here.  Will have
to check.  It is working, but have always wanted to make an endpoint
adjustment.  Perhaps a 12BA6 will save the need for this adjustment.

As mentioned, another way is to solder-jumper 2&4 and 5&7 and plug in a
12BH7.  The 12-volt filament of the 12BH7 drops the voltage in a somewhat
similar amount as the ballast tube.

Merry Christmas and Happy Holidays!

73 de Bill, AB6MT
[email protected]

----- Original Message -----
From: "Jim Shorney" <[email protected]>
To: "Helmut Usbeck" <[email protected]>
Cc: <[email protected]>
Sent: Sunday, December 22, 2002 3:33 PM
Subject: Re: [R-390] in rush current limiters

> -----BEGIN PGP SIGNED MESSAGE-----
>
> On Sun, 22 Dec 2002 17:38:56 -0500 (Eastern Standard Time), Helmut
> Usbeck wrote:
>
>
> >Haven't been able to find a manufacturer that
> >makes a constant current diode with a high enough rating yet, which would
> >be a nice replacement for the 3TF7.
>
>
> Question, then: what is the regulating current of this curious tube?
> Three-terminal regulators can be configured as constant-current
> devices.
>
> - --
> Jim Shorney      -->.<--Put complaints in this box
> [email protected]
> [email protected]
> Ham Radio NU0C
> Lincoln, NE, USA
> EN10PT
> http://incolor.inetnebr.com/jshorney/
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