[Collins] 75A-* help needed here!

[Dr. Gerald N. Johnson]

On Sat, 2010-01-23 at 16:28 -0600, Joe Eide wrote:
> Hello friends,
> 
> I hope someone can or will help me.
> 
> I desperately need a *coil for my 75A-4*.  There are 2 of these in every 
> 75A-2,  75A-3 & 75A-4. 
> It is the *40 meter* *RF* or  the 40 meter *mixer coil*.  Collins part 
> number is 504 7000 001.

I can't tell from the downloaded manuals that are most handy exactly
what the construction is. There's a hint the coil forms snap in, and so
are likely phenolic. Judging by the adjacent ceramic trimmers, I'd guess
the coil form is 3/8" outside diameter, probably has lugs that wrap most
of the way around the form. The books all say 18 turns #28 DS. Thats
double silk insulation, not handy today. I'd suggest #28 enameled wire
wound with a heavy thread (like button thread) as a temporary spacer,
then anchored with Q-dope. Likely the end of the slug is painted red to
indicate the mix. That's an important factor too.

The coil forms for the other bands appear to be the same in these
pictures.

The 504 part number indicates the coil was wound by Collins, not
purchased.

There is probably something similar in my shoe box of small slug tuned
coils but I need to know more about the mounting and the coil details to
pick something to work. Slug tuned coils that size are probably still
made by J.W. Miller but not carried by any distributors. The threads of
the slug are also important. Else finding the coil will require finding
a 75A. being parted out. Haven't one in any condition here to look at.

I notice that one of the three receiver manuals shows 300 pf tuning the
RF coil and 270 pf (plus a variable in all cases) tuning the other two
receiver RF coils and all the mixer coils. Makes me wonder if the 300 pf
value on the schematic might be in error.
> 
> I think my slug is ok, but wouldn't mind having the set so I know they 
> will work together.  I can't try rewinding because the coil form was 
> destroyed.
> 
> Please help me if you can.  Just let me know what I can pay you.
> 
> 73,
> 
> Joe - KB9R

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer