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  Radios...

[29 July 2022] I was handed one of these to tinker with:

It's a НПП Б3РП - ПРИЕМНИК РАДИОВЕЩАТЕЛЬНЫЙ... aka, a Russian Radio (NPP B3RP-309), it features USB and SD card input so not exactly a vintage collector's item, nor a particularly "quality" item. It was intriguing to me how it found it's way here to the UK; perhaps a Ukrainian brought it with them to the UK.

The radio was not working, or rather, not directly from the mains. Helpfully, it accepts various power inputs; batteries, and also via 6V adapter.

I tried it with the latter and it switched on so I opened it up to investigate further (four screws with one hidden in the corner of the battery compartment) - the back and front then come away from the central wooden part.

Prior to opening it I realised upon a second test with my AC adapter that the socket had pushed inside, so I had that to repair.


An extra washer was required to better hold the 6V socket in place.

I first found the wire that goes to the aerial had come detached, perhaps it came off when I opened up the system but it must have been only just attached if this was the case - the end at the PCB was also flimsy. The wire seemed to be poor as a whole so I replaced it with a thicker wire. A simple fix, but clearly not related to the power problem.

Everything else checked out, there simply wasn't 6V coming from the transformer and I noticed the wires joining seemed to have heat damage and were brittle. It seems the transformer has burnt out.

There were no markings on the transformer itself so I looked on ebay for 6V transformers since that was what the radio required. I found these for 7.34.

I was not convinced this was the cheapest option and I thought a dedicated 6V AC adapter would be more cost effective, and I found one of these for 4.88.

 

 
Side note:
Power transformers convert the mains AC power (in this case 230V used in both Russia and the UK) down to a rated DC voltage (in this case 6V). They also need to be capable of providing sufficient current for the device (typically rated in mA, or A - milliamps, or amps respectively - 500mA is half an Amp) - the device, such as your laptop, or this radio, should state this on a label, sometimes this is given in Amps or in Wattage, which is V x A. Therefore, your laptop's charger might state 19V at 2.3A, which would be around 45W. Some laptops are more power hungry and require 75W which could mean the wrong charger would fail, or at least get very hot.

Both of these options were listed as 1A and therefore better suited than the 300mA adjustable one I'd used for testing. There is no label on the radio stating the current draw/wattage so I can only assume that the original transformer suffered from the unit being played at too high a volume that it could cope with for any length of time. Other than testing the unit at various volumes with a test meter I don't know how else to determine the maximum current draw from the radio to ensure the correct transformer or adapter is used.

Thinking a little more I realised that the AC adapter simply contains a transformer [plus some simple circuitry to dictate the polarity], but I would save 2.46 by buying it encased in plastic instead of a standalone transformer! I quite like the idea of repairing the radio properly and being able to use a simple power lead, however I have a cheaper option still: I will look out for a second-hand 6V AC adapter at the thrift store that I can remove the transformer from.

- - - - -

[August 2023] This is one of those projects that simply sits on my "repair pile" for far too long, but today I got to it.

I had a 6V AC adapter that I bought from the thrift store for no more than 1. It was rated at 500mA, so I hoped this would be sufficient.

I set about cracking open the plastic casing with a screwdriver and a hammer (yes this is the way*).

*I have had to do this to a laptop charger with a faulty cable, so it's not ideal when you want to put it back together in a neat manner.

Here is the transformer inside:

I actually discovered the wires connected to the plugs prongs to allow in the 230V were loose with dry/broken solder; quite concerning that this would have gone unnoticed and would likely have been causing some arking - I wonder how common this issue is in power adapters...

Side-by-side it was clear that the replacement transformer (left) was larger than the original, this was good news in the sense it surely meant it was capable of supplying more current than the original, but would be bad new if it doesn't fit the space available in the radio...

Thankfully it did indeed fit; I had to use part of the bracket that encased the original transformer, and I could only hold it in place with one of the original two screws, but this felt adequate. The soldering of the wires went well, in fact further dry joints were found on the end of the wires where they join the radio's main circuit board, so I was able to address that too. (I think I am correct in saying it doesn't matter which way the wires are connected since the mains power lead can be inserted either way, and both wires from the other side of the transformer are simply blue with no stated polarity.)

A quick test revealed all is working.

I found a user manual [here]

Translated, it states: "The radio receiver... is designed to receive... broadcasting stations in the medium wave, short-wave, and tame(?) in the range of ultrashort VHF..."

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