[Milsurplus] Collins 51S-1

[Paul Kraemer]

Jim
May I suggest two mos fets instead of the two transistor power supply. Much 
better approach when you drive them with a sqare wave from a little cmos 
logic.
I've done this before and have some interesting notes on vibrator 
replacement solutions / low voltage supplies.
Paul K0UYA
----- Original Message ----- 
From: "Jim Whartenby" <antqradio at sbcglobal.net>
To: <milsurplus at mailman.qth.net>
Sent: Friday, August 12, 2011 9:05 PM
Subject: [Milsurplus] Collins 51S-1


>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
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