I purchased a Collins 51S1-A, the 28 volt DC, receiver that had been converted to 120 volts AC. It looks all Collins on the inside, so I am curious if there was a kit to do this or if the person doing it bought the Collins parts to do so. The wiring looks very professional, almost too good to be done in someone’s garage. However, it is wired only for 120 volts, it has the correct dual primary transformer but the wiring is not such that it can be operated on 240 volts with a power cord having the proper jumpers in the connector. Does anyone have any thoughts or information on such conversions?

Howdy,

You can get a little insight on how this "conversion" was accomplished by looking at the 51S-1 manual.

The CCA has a copy of the manual that is in the public domain that shows how Collins did the 28V DC power supply that is essentially the same as other amateur radio manufacturers did it (I.E. Drake, Hallicrafters, Heathkit, etc) except they did it using an external power supply that not only operated on 12V DC but also supplied voltages for the transmitter sections of a transceiver ....and in the case of the Drake DC-4, it could even power a complete Drake C-Line (transmitter and receiver)

You can have a look at the manual here: http://collinsradio.org/archives/manual ... ceiver.pdf



It's pretty clear that they placed a simple solid state switching type DC power supply in a "box" that provides the correct DC voltages and mounted it on the chassis where the 60Hz transformer/rectifiers and capacitors would be placed, possibly using the same mounting holes to facilitate the manufacturing process so any 51S-1 could be retrofitted with the 28V DC power supply chassis in the field with maybe a few other wiring changes to accommodate the different filament wiring.

Anyone could also convert back if they desired once the correct transformers and other components were obtained (and even do it their "garage"!!) since they would be mounting the transformer/caps etc in already present mounting holes etc.

The only "Collins part" required would likely be actual power transformer for probably any 75S- receiver. I think those are in abundant supply new (old stock) and used. The rest of the parts would be pretty generic.


Cheers,


Rick

Thanks Rick. I have studied the manual and it is a help, but I am still not exactly sure about the conversion back to line voltage. By the way, the power transformer is not the same as the 75s series, but I have a proper transformer and the radio works just fine. I don't think I would convert it back even if I found the proper power supply, this conversion is part if its history.

Yeah,

More than likely, someone just used a suitable transformer with the correct voltages and even so, I probably wouldn't try convert it back to 28V either unless I had a bunch of other stuff that operated on 28V DC.

About a year ago, I acquired a Drake TR-4C in nearly mint condition that also had the Drake DC-4 DC power supply with it. I completely rebuilt the DC-4 and I have to say, the DC-4 works flawlessly!

If I was going to set up a 12V solar charged power system, I would seriously consider using the DC-4! It does draw a fair amount of "stand-by" current (around 10A) but it works so well, I wouldn't hesitate to use it!

The 51S-1 with the DC power supply installed would probably only draw around 3-5A @28V during normal operation.

Good luck with your 51S-1!

73/Rick

The conversion from 28VDC to 120 VAC was done with the correct Collins parts making it look to me like there may have been a kit sold by Collins. The only thing different from an original is that the power socket and primaries of the power transformer are not wired in such a way as to be able to switch to 240 volts input by simply plugging in a power cord with the correct jumpers in the plug. It is wired for 120 volts only. Who ever did the wiring did a really nice job though. Some place at some time I saw something about some conversion and it said to place the correct sticker next to the power input socket - either 120 or 240 volts. I can not recall where I saw this or even if it was for the 51S-1 radio. Of course looking through all of the Collins books that I can find, I can not find where I saw this.

Well the question is kind of answered. In looking through a lot of Collins documents, I found an instruction manual for the kit to change the AC power supply to DC and another to change the DC power supply to AC. It looks like what was done to my radio. So Collins did make a kit to do this and it is interesting that there were three kits, one for 120 volt, a different one for 220 volt and a third for 28 volt. You would end up with a radio that was not dual voltage AC.