[Boatanchors] CE 20A Undocumented Mods?

[K3PID]

Well I removed the extra parts and also a pot that had been added in place
of the 2.7K "relay sensitivity" resistor. Now I've started tracing the
complete circuit to make sure there isn't something else lurking!! I hope to
have power on it by New Years Day!!!

Tnx fer the help!
K3PID
Ron H.



----- Original Message ----- 
From: "James M. Walker" <chejmw at acsu.buffalo.edu>
To: "K3PID" <k3pid at sbcglobal.net>; <boatanchors at mailman.qth.net>
Sent: Monday, December 26, 2005 12:52 PM
Subject: Re: [Boatanchors] CE 20A Undocumented Mods?


> 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.
> >
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> >
> >
> >
>
>