[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.  The power supply is very compact and it is 
well executed.  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, but the power transistors in the 
power supply are dated 8727!  The 51S-1 has a 3810 serial number. 

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?

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.
Jim