[Boatanchors] CE 20A Undocumented Mods?

[James M. Walker]

Hello Ron and list,
I tried to figure out what that would be, can't think of anything yet!

It has been my experience that a lot of undocumented mods were
done to these 20As. I have refurbished/repaired 4 total, two of the
desktop, and two of the rack mount, none of which had anything like
the mod you describe. Although there were some strange ones in a
few of them, all since removed, (MILTFDJ-1) is how I approach them.

Someone changed the rectifier out (5U4GA) with a homebuilt stack
of diodes on a piece of perfboard, in an octal socket. The HV was
sitting at 600 VDC and parts were smoked all through the thing. I put
it back like the drawing, changed the burned parts and replaced the
6AG7s and the 12BH7 and that brought the thing back to life.

Then it was just a process of tracing the signal through stages with
an RF probe and replacing open caps and the like, a pain but not
to bad.

My guess says remove it and make it like the manual, and check for proper
operation. I looked through all my documentation and can't find that
in there anywhere.

Jim
WB2FCN
http://eshop1.chem.buffalo.edu/Central-Electronics.htm

----- Original Message -----
From: "K3PID" <k3pid at sbcglobal.net>
To: <boatanchors at mailman.qth.net>
Sent: Sunday, December 25, 2005 8:55 PM
Subject: [Boatanchors] CE 20A Undocumented Mods?


> HELP!
>  I am in the process of rebuilding a Central Electronics 20A and seem to
> have an undocumented modification. As far as I can tell all of the mods
> noted in the BAMA site are installed and complete. There are however two 5
> amp diodes in series with the anode end grounded and the cathode tied to
pin
> 1 of the 6AL5. The junction of the two diodes is connected thru a 33pf cap
> to the junction of C42 & R77. None of this makes sense because the #1
> cathode (pin 1) of the 6AL5 is only normally at -.5 volts and couldn't
> provide enough voltage to forward bias the diodes. The junction of C42 &
R77
> is at -100 volts in stand-by and ground for transmit. Since the
undocumented
> 33pf cap is polarized with the cathode end at the C42-R77 junction, I
> suppose it could charge up to the -100 volts and serve some sort of spike
> suppression when switched to transmit.
>
> Anyone familure with this mod? Can you explain it?
>
> Thanks
> K3PID Ron H.
>
> _______________________________________________
> Boatanchors mailing list
> Boatanchors at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/boatanchors
> ** List Administrator - Duane Fischer, W8DBF/W9WZE **
> ** For Assistance: dfischer at usol.com **
> $$ For vintage radio info, see the HCI web site $$
> http://www.w9wze.org
>
>
>