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Crystal sets, POW radios, spy sets & radio related thread

AlienFTM

MIA
Book Reviewer
This just cropped up in my Instagram feed.

I don't normally follow this thread, so apologies if it's been published already.

 
This just cropped up in my Instagram feed.

I don't normally follow this thread, so apologies if it's been published already.

Intriguing. I haven't seen this one before. Do you have any more photos of this miniature radio? I can see the antenna wire in it's tidy away position and a large capacitor (condenser). One source of power could have been the overhead light sockets, though some POWs would be adept at tapping electrical wires where possible.

The only way to get fresh batteries would be theft, blackmail, a sympathetic guard or smuggled by MI9 in a Red Cross parcel. Standard valves would require a low voltage battery for the valve heaters and a high voltage battery for the valve HT supply. The 31/1 below used a standard 4.5V torch battery, which some of us may remember and a 30V hearing aid battery. Supposedly this would last 200 hours.

Manufacturers of the better known miniature radios included Philco, Hale and others.

The following were made for the SOE but intended for use by operatives rather than POWs. More details via the links and well worth a look. Although the circuits look simple, this was very impressive miniaturisation for the time.

MCR 1 "Biscuit Tin" radio receiver from late 1943

1603107338610.png

MCR-1

31/1 "Sweetheart" from 1943

1603107498495.png


Sweetheart
 

AlienFTM

MIA
Book Reviewer
Intriguing. I haven't seen this one before. Do you have any more photos of this miniature radio? I can see the antenna wire in it's tidy away position and a large capacitor (condenser). One source of power could have been the overhead light sockets, though some POWs would be adept at tapping electrical wires where possible.

The only way to get fresh batteries would be theft, blackmail, a sympathetic guard or smuggled by MI9 in a Red Cross parcel. Standard valves would require a low voltage battery for the valve heaters and a high voltage battery for the valve HT supply. The 31/1 below used a standard 4.5V torch battery, which some of us may remember and a 30V hearing aid battery. Supposedly this would last 200 hours.

Manufacturers of the better known miniature radios included Philco, Hale and others.

The following were made for the SOE but intended for use by operatives rather than POWs. More details via the links and well worth a look.

MCR 1 "Biscuit Tin" radio receiver from late 1943

View attachment 513357
MCR-1

31/1 "Sweetheart" from 1943

View attachment 513358

Sweetheart
Sadly not. I've since seen that Tank Museum have also published it on their Facebook feed. Maybe there's more, and discussion.
 
Sadly not. I've since seen that Tank Museum have also published it on their Facebook feed. Maybe there's more, and discussion.
Found the full size photo, thanks.
R-full.jpg


Found this interesting account of POW camp radios:
Secret Camp Radios - John Chew PoW History

Here is an excellent clip of a testimonial by a BEF medic who was ordered to stay behind at Dunkirk and spent five years as a POW. It features his radio which was made by the Polish underground, smuggled in and hidden behind a loose brick. It was still there when he visited the camp 60 years later!

BBC One - Antiques Roadshow, Series 34, Remembrance Special, Antiques Roadshow Remembrance Special - POW Radio
 
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On looking at the full size photo, it looks like there are five acorn valves (tubes). I was puzzled by the 95 on one tube as there should be a three figure number. Looking more closely it's a trick of the lighting. I think it's a 955, which was a mains powered VHF/UHF tube. That does not mean the set was designed for VHF however. If it had been a 958 that was a battery powered tube. The 955 is specified as a detector/oscillator/amplifier. It is very likely a superhet, which though detectable with direction finding equipment was far less so than a simpler regenerative set.

ETA - despite the 955 being specified for mains voltage, I found a design from 1945 for a one tube receiver using a 955 acorn tube, which requires a 45V battery for the HT and four standard flashlight cells for the heater. https://www.radiomuseum.org/forumdata/upload/Mbs_1945.pdf
 
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On looking at the full size photo, it looks like there are five acorn valves (tubes). I was puzzled by the 95 on one tube as there should be a three figure number. Looking more closely it's a trick of the lighting. I think it's a 955, which was a mains powered VHF/UHF tube. That does not mean the set was designed for VHF however. If it had been a 958 that was a battery powered tube. The 955 is specified as a detector/oscillator/amplifier. It is very likely a superhet, which though detectable with direction finding equipment was far less so than a simpler regenerative set.

ETA - despite the 955 being specified for mains voltage, I found a design from 1945 for a one tube receiver using a 955 acorn tube, which requires a 45V battery for the HT and four standard flashlight cells for the heater. https://www.radiomuseum.org/forumdata/upload/Mbs_1945.pdf

I thought that also .... no base but with fly away leads for connection and could operate with a relatively low HT ... IIRC they were quite common in car radios with the HT coming from a Mechanical Vibrator , Oooh Er Mrs ,
 
Have been playing with the science kit- and testing / tweaking my crystal radios.

2020-10-27 16.07.35.jpg


I've got about 10m of wire Im using as an aerial run through dining room. Reception as expected is not that great. Can just make out actual 'voice' of some sorts.

Using the science kit and associated modules I sought to test out my crystal radios by making the following:

2020-10-27 16.08.09.jpg

2020-10-27 16.08.24.jpg


I got the square root of feck all listening on my crystal radios whilst using the above. Could somebody explain why please?
There is an AM transmitter project also which I might dabble with.

My ultimate aim is to get my lad into this stuff but - I need to prove concept and myself have a decent understanding first otherwise...he'd lose interest and just revert to minecraft / Nintendo Switch etc.
 
Have been playing with the science kit- and testing / tweaking my crystal radios.

View attachment 515601

I've got about 10m of wire Im using as an aerial run through dining room. Reception as expected is not that great. Can just make out actual 'voice' of some sorts.

Using the science kit and associated modules I sought to test out my crystal radios by making the following:

View attachment 515602
View attachment 515603

I got the square root of feck all listening on my crystal radios whilst using the above. Could somebody explain why please?
There is an AM transmitter project also which I might dabble with.

My ultimate aim is to get my lad into this stuff but - I need to prove concept and myself have a decent understanding first otherwise...he'd lose interest and just revert to minecraft / Nintendo Switch etc.

From what I can see there, I have absolutely no idea how you would determine the Tx frequency without some sort of extra device (e.g. Frequency counter, spectrum analyser etc.). Essentially you have an oscillator producing a carrier frequency that you turn on and off ('Make' and 'break') with the morse key. The only way to find the carrier blind, is to leave the morse key 'made' and then tune up and down your receiver until you hear the tone.

I assume that the transformer primary (Between 58 and 66) is providing the inductance (L) that is working with the variable capacitor (Between 135 and 136) (C) to produce the tuning frequency. Unless you know what those values are, you have to tune blind as I described above. However if you do know the values then the resonant frequency will be somewhere around the area of:

f = 1 /(2 Л √LC) Hz

I say 'around the area of', because the other cct components will have an influence too.
 
Whilst perusing YouTube and watching stuff about HAM foundation course I came across this:


Its an online tool where you can build your own circuits and tweak values / see what changes take effect.

Its something my little lad is soon going to be introduced to.
 

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