[MRCA] [MMRCG] Soviet R-107

[Ray Fantini]

Thanks for the responses, once again real people prevail over AI. Li batteries are appealing, and so is the idea of using the original cells. Attached is a picture of the KNP-20 that’s a dual pack 20 Ah 2.5 volt monster. The radio only uses two packs but like everything else in the world once you start down a road a lot of bits and peace tend to follow. The cleanest cell is one that has never been filed, the ugliest cell is what they tend to look like when left to their own device. The Russians also covered these things with wax and for a while when running the radio I tried dumping hot wax and it did tend to keep the weirdness down.
Think the KNP-20 is used in a bunch of other devices but know it’s shaped a little different from what’s stuffed up R-311 although its 2.5 volts also.
I built up a small circuit that allows the radio to work from a signal six-volt source. Just added a signal high current diode in series with the six volt source and somewhat independent of current provides a good three quarter volt drop so fix voltage drop across a forward biased diode turns out way better then resistors or solid state regulation.
I was in error earlier though; turns out the radio sucks down almost one amp in receive and two in transmit for a booming three quarters watt of FM power. Figure a 7 Ah SLA will be enough for most duties although I think the 51.0 “Cold War” net at the Hamvention ran for over an hour this last time. Good thing I am not NCS for that

Ray F/KA3EKH


________________________________
From: MMRCG at groups.io <MMRCG at groups.io> on behalf of Albert Marsh via groups.io <hitekgearhead=hotmail.com at groups.io>
Sent: Saturday, November 15, 2025 12:02 PM
To: Walter J. Skavinsky (KB3SBC) <Kb3sbc at comcast.net>; MMRCG at groups.io <MMRCG at groups.io>
Subject: Re: [MMRCG] Soviet R-107



If the original battery was a rechargeable nickel based chemistry why not go with something similar to avoid voltage differences? I understand that SLA is easy but they have their own drawbacks also.

Depending upon the physical size of that original battery, I might weld up two packs of slow self discharge nickel metal hydride cells, tap them in the center just like the original, and Bob's your uncle.

I am sure that modern NiMH cells have a lot more capacity than that original wet cell and they certainly will not leak unless you abuse them. (At least I have never had one leak)

For instance, if that 2.5V battery was say the size of a coffee cup, I might take two Tenergy Centura D cells which have a 8Ah capacity and weld them together in series. There would be your 2.5V battery.

Make a pair of those and you would be all set.

No control electronics necessary unless you might want to put an inline polyfuse in the pack just for good measure.

What do those original batteries look like? How big are they?

BTW, as a side note, I came across this same problem with a Russian military dive light. (I also collect flashlights and lanterns) The rechargeable wet cells were potted into the case with wax. That was FUN to disassemble. Luckily the case was cast aluminum and a lot a patience with the heat gun prevailed.


-Albert
KI4ORI
_._,_._,_
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