[Collins] 51S-1

[Dr. Gerald N. Johnson]

Back in 1964 my boss at Collins caught me in the lab one day drooling 
over a 51S-1. I explained I was shopping for a ham receiver. He said he 
had been in charge of the S-line and the 51S-1 and that the 75S-3B with 
a crystal pack was a much better receiver than the 51S-1. So I bought a 
75S-3B and modified with one extra crystal socket (along with many other 
mods) and still have it. I didn't get a crystal pack until sometime in 
the early 70s.

Some 51S-1 were made to run from 28 volts DC, and some from 120 volts 
AC, but all ran 28 volts on the series parallel heater/lamp string.

When I worked at Collins there was more than one S-line built from parts 
purchased from Collins surplus and from Collins parts where they would 
sell parts to employees from the same bins used in the labs to build 
stuff for work. But once they noticed an employee demand for 70K-1 PTOs 
they stopped selling them except in the second PTO console which made 
building the S-line more difficult. That could be the source of the 
power supply in your 51S-1. Or a ham got one with a smoked supply and 
the germanium power transistors were too hard or impossible along with 
the custom transformer and a more stock transformer with center tap was 
easier to find and that ham was experienced at designing circuits and 
did a one of. Collins labs use G-10 for prototype circuits by the square 
yards, maybe square miles and there was always a supply of it encumbered 
with Vector pins and parts at the surplus store. Also many teflon 
insulated pins.

On 8/13/2011 10:01 PM, Jim Whartenby wrote:
> 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
> ______________________________________________________________
>
The Cedar Rapids hamfest has pretty consistently been the finest one in 
the area, except its a poor place to sell Collins equipment, there's 
much in circulation and the prices are low.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.