[Collins] Re: 75S3 Questions

[Dr. Gerald N. Johnson]

On Tue, 2008-02-12 at 15:28 -0500, Bill Stewart wrote:
> Man, what a great response to my questions. Many thanks to all who 
> responded.
> 
> I have shut the receiver down, except for some testing. In previously 
> looking around the rcvr, I did note that there were only five of the paper, 
> tubular capacitors...all Sangamo and I believe either .1 or .05's. They will 
> be replaced. The coupling cap to the grid of the 6BF5 is a disc. I think 
> disc caps usually hold up ok, but will check the 6BF5 grid bias.  Also, 
> someone mentioned the bias rectifier being a S/T cube...that's what I have. 
> I will replace it with a 1N4007, same as used for the B+ diodes.

Mount a two terminal without ground terminal (solder tag) strip in place
of the selenium and mount the new diode on that. There's a strong chance
that will cool both the 6BF6 and the power transformer, though the tube
will alway be fairly hot. Hence the dark spot on the cabinet lid over
it.

> It does 
> have 150vdc B+. I think the fuse-block diode mounting was orig with this 
> rcvr since the mounting nuts have some loc-tite on them.

Shouldn't have been loc-tite, but a colored lacquer also on the solder
connections. The inspector put a drop on each inspected and passed
solder connection.
> 
> The B+ 'lytic in my rcvr is a Sprague with twist lock tabs, 183-1764-00 (may 
> be a Collins in-house number).

That IS the Collins part number. The 183 group was all electrolytic
capacitors.

> It is 40/40/40 uf @250vdc. It is about 1 inch 
> in dia. The ones I found at Surplus Sales was 40/40/20 at 450vdc 1.5 in. dia 
> and another was 40 at 350vdc and 40/40 at 300vdc 1 3/8 in. dia. I'm not sure 
> if either of these would fit the chassis slots for the twist tabs. Anyone 
> know for sure. I may try my hand at restuffing first.

They did come in different mounting diameters and the big ones won't
stuff into a small hole even with a big hammer.

> 
> I did receive the manual on cd today and its the forth edition, 1 jul 1963. 
> It's not the exact manual for my rcvr but will do for a while.

Probably for 3B/C. Won't match your receiver several places. Was hard to
read. I wrote the next edition.

The right manual should be down loadable from CCA manuals.

> By the way, 
> if anyone needs to copy this version of the manual, let me know and you can 
> borrow my cd.
> 
> On the S-meter illumination, I noticed the inside of my S-meter is black. 
> The inside of my 30L1 meter is white.
> 
> Guess that brings me up to date for now. I have some other questions re: hum 
> and some squealing at close to max volume. These problems may go away after 
> I re-cap so will hold off on these questions.

Signs the big electrolytics are bad (as are the couple little ones).
> 
> Again, many thanks for all the help...it IS a real nice rcvr...73 de Bill 
> K4JYS 
> 
> 

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