[Milsurplus] Collins 51S-1

[Jim Whartenby]

I got lucky at the Cedar Rapids Hamfest last week and picked up the above.  The 
only issues are that it is missing the cabinet and it has a 28 volt power supply 
installed.  No corrosion other then a funky deposit on the black tube sockets 
which look a lot like lime deposits.

A closer look at the power supply indicates that this is not the one in the 
51S-1 manual that is on the CCA website.  The 28 volt power supply in the manual 
uses 4 switching power transistors but this power supply only has two.  So the 
power transformer must have a center tap as opposed to the one in the manual 
which is switched in bridge mode.  It is very compact and it was 
well executed with a high standard of shop practice.  Lots of perforated G-10 
circuit boards so I guess it is all hand wired.  I will have to take it apart to 
check the electrolytic capacitors anyway so there is plenty of time to check 
things out further.

There is a tag on the chassis so the receiver started life as a 120/240VAC 
powered radio.  The only date code I saw was on the only original transistor in 
the radio.  Q1 was made the week of 6531, the 51S-1 has a 3810 serial number. 
 But the power transistors in the power supply are dated 8727!

Two questions:
Anyone have a spare cabinet?  (One can dream, can't one?)
Anyone have a schematic for the two transistor 28 volt power supply?

Also seen at the fest was a 51J-4 with both top and bottom covers in great shape 
that went for only $200.00  (I was 30 seconds too late on that one!)  There was 
one out in the fleamarket in a desk cabinet with a $400 price on it but it was 
unsold when I left at 11AM.  Lots of other boatanchors were seen such as more 
National receivers then I have ever seen in one place.  There were also Tek 
scopes and other examples of test equipment, some parts and quite a few other 
bargains, but unfortunately, I have little room to spare in the VW Jetta.

Besides the receiver, I picked up a box of 20 or so two and three pin NOS 
military style AC power cable connectors and a cup of about 50 74XX series TTL 
ICs.

This was a nice fest, well organized and well run with lots of occupied tables 
inside and out.  If I lived closer, I would definitely go again next year.

The wife and I are heading to Oregon for a family wedding on the 20th, anything 
out there I should look into?
Jim