Telephone set F

[Phil G4SPZ]

Originally Posted by russell_w_b

...I don't think there's any risk of frying your mic on 12V. I seem to recall measuring the voltage across the mic on my CB-connected type 332 instrument and it being around 12V. As I said, the mic (Inset, No:13) will work quite happily from 30 - 200mA so you should be OK... when I get home I'll check the voltage across the mics in my 332 and in my wall-mounted Ericsson N1071. I'll get back with the measurements.

Russell, thanks for that and I appreciate the information. Out of interest, my telephones came with mic inserts labelled "YA 1077 Mk IV" - is this similar to an Insert No:13? I also obtained two identical inserts from a "Microphone Hand No 4A" and a "Microphone Hand No 8".

Originally Posted by russell_w_b

Over what sort of distance are you testing your telephones?

Just a few feet of bell flex at the moment, although the XYL has promised to help me run a test over 30 metres later tonight, using 3 volt batteries as per the original specification. I only really need these telephones to work over a few hundred metres. I am, however, interested in how these instruments worked in the field with 3V batteries... were the signallers expected to bellow into them?!

Thanks for all the advice,

[russell_w_b]

Originally Posted by Phil G4SPZ

Russell, thanks for that and I appreciate the information. Out of interest, my telephones came with mic inserts labelled "YA 1077 Mk IV" - is this similar to an Insert No:13? I also obtained two identical inserts from a "Microphone Hand No 4A" and a "Microphone Hand No 8".

Ha! I had a couple of those; used on 'Wireless Set No: 18'. The inserts are the same, I think. Mic. Inset No:13 is similar to earlier Mic. Inset No:10, but I don't know if the electrical characteristics are different.

I'll get back to you about the voltages later, but it's occurred to me that you should check the induction coils in your telephones. Any damage visible? Can you buzz out the pins on the ends of the ASTICs and check out continuity WRT the drawing? I think it unlikely that you will have shorted turns on them, particularly as your low-level sound is on both instruments, but it may be worth a look. Some ASTICs have their resistances written on a slip of paper, visible beneath the outer layer.

Is the sound level different when the telephones are connected to when they're open-cct?

[russell_w_b]

Originally Posted by dkleeman

This has inspired me to try to revive my set. There are some good photos of this telephone set here.

I see this particular instrument has a modified handset, converted to take a DLR5 balanced-armature receiver. - or was there a version made with this type of receiver to start with? I've had four 'F' Mk II's, and this is the first one I've seen like this.

It also looks slightly more modern than others I've seen. Anyone know when the type 'F's were superseded?

[Phil G4SPZ]

Russell,

I've tried the phones on 3 volts over 30 metres or so of thin bell wire, and although the volume is relatively low, it is acceptable. The sound in the earpiece is roughly the same when o/c as when linked by the line. I haven't tested the induction coils but they look perfect.

It has struck me that I am using non-identical telephones together, an F and a D. I imagined they would be compatible, but maybe there's a line impedance mismatch? Anyway, I've got another F Mk II on its way, so I'll try the matching pair at the weekend and report back!

Thanks for your continuing help and interest.

[russell_w_b]

Originally Posted by Phil G4SPZ

Russell,


It has struck me that I am using non-identical telephones together, an F and a D. I imagined they would be compatible, but maybe there's a line impedance mismatch? Anyway, I've got another F Mk II on its way, so I'll try the matching pair at the weekend and report back!

Phil,

I was miles out with my 12V across the mic before; don't know what I was thinking of! Here are the measurements made on three telephones at Chez Barnes:

• Siemens Bros 366 (wiring same as BPO 162): 2.5V @ 15mA.
• Ericsson 1071: 5.1V @ 40mA.
• BPO type 332: 6.5V @ 40mA

I've never found mixing telephones to be a problem.

[Phil G4SPZ]

Interesting development - my second type "F" telephone has arrived, a non-buzzer model marked 'Telephone set "F" Mk II TMC'. It has exactly the same earpiece as in the photo posted by dkleeman, and is much more sensitive than my first phone which is badged 'Telephone set "F" Mk II PL' and has a traditional earpiece. Perhaps TMC stands for 'Telephone Manufacturing Company' and PL may be short for 'Plessey'?

Anyway, back to battery voltages... the TMC phone gives good audio when the PL phone is working from just 3 volts, but I have had to put a 6-volt battery into the TMC phone in order to get roughly equal audio level in the PL phone's earpiece. It would therefore appear that development led to the more sensitive earpiece being introduced to improve the audio level, rather than increasing the battery voltage - probably because there was no space for more S or X cells!

Anyway, thanks to one and all for the interesting information you have supplied, and I am now pleased to own a working pair of Telephone Sets "F".

[russell_w_b]

Originally Posted by Phil G4SPZ

Interesting development - my second type "F" telephone has arrived, a non-buzzer model marked 'Telephone set "F" Mk II TMC'. It has exactly the same earpiece as in the photo posted by dkleeman, and is much more sensitive than my first phone which is badged 'Telephone set "F" Mk II PL' and has a traditional earpiece. Perhaps TMC stands for 'Telephone Manufacturing Company' and PL may be short for 'Plessey'?

You are correct about the TMC. I'll have to look and see who made mine! I suspect the earpiece on yours was an approved miltary modification, as a balanced-armature receiver unit is fitted, the new-type as fitted to the type 706 telephone onwards. An older version of b/a earpiece was fitted to DLR5 type headphones. These were low-impedance headphones used, amongst other places, on 'Fullerphones' - a morse-telegraph comms unit not unlike the field-telephone, but a unit which worked over phoenominally long distances and was very sensitive indeed.

I have one military 'J'-type field-telephone fitted with such a receiver, and two civilian type-'J's (they're brown, not green) with the traditional 'Receiver, Inset, No:11' type of earpiece. There is certainly a difference in sensitivity.

I'm pleased you got satisfaction in the end. What do you propose using them for?

[Phil G4SPZ]

Originally Posted by russell_w_b

I'm pleased you got satisfaction in the end. What do you propose using them for?

It's a long story, but with the Moderators' permission I'll respond here rather than via PM, and I'll try to keep it short... I have a pair of ex-military LSDSR units ("lamps, signalling, daylight, short range") and I use these every October on an event known as "Jamboree On The Air" or JOTA. Amateur radio clubs and operators assist Scout leaders to set up special event ham radio stations worldwide and put on allied activities related to electronics and radio, and with my own interest being Morse Code I run an activity where groups of Scouts and Cubs learn a little Morse and send simple messages to each other.

To avoid licencing difficulties I use the LSDSRs, which are land-based Aldis lamps capable of several miles range, although we use them over a path of just a few hundred yards. Talk-back between the adult instructors at each end has previously been via amateur radio, meaning that the activity requires two licenced hams - sometimes that's difficult on a busy weekend, so the field telephones have been obtained to permit non-licenced instructors to run the activity! It also will give the youngsters experience on another type of communications device.

Thanks for your help in getting the phones going!

[russell_w_b]

Originally Posted by Phil G4SPZ

Interesting development - my second type "F" telephone has arrived, a non-buzzer model marked 'Telephone set "F" Mk II TMC'. It has exactly the same earpiece as in the photo posted by dkleeman, and is much more sensitive than my first phone which is badged 'Telephone set "F" Mk II PL' and has a traditional earpiece. Perhaps TMC stands for 'Telephone Manufacturing Company' and PL may be short for 'Plessey'?

Out of curiosity, can you unscrew the earpiece cover? If so, is it fitted with a 'new' type balanced-armature unit? It may indicate use of your telephone into the 1960's. Does it look like this (below)?

Regarding your use: best of luck! I did more-or-less the same thing with the Cubs. I taught them a bit of morse, and I have two Aldis lamps which I used similarly. We used short-range PMR446 walkie-talkies, though.

[Dave Moll]

I'm glad to see them being put to a real use.

Perhaps your next acquisition should be a pair of telephone sets "D", complete with morse keys, to give yet another communications experience - but that would be a topic for another discussion. I can't imagine the buzzer button on an "F" (even if both are equipped with buzzer-type inductors) being particularly useable for morse sending.

[Phil G4SPZ]

Originally Posted by Dave Moll

I'm glad to see them being put to a real use.

Perhaps your next acquisition should be a pair of telephone sets "D", complete with morse keys, to give yet another communications experience...

Hi Dave,

Well, I've got one type "D" already, so that's a good idea, and if anyone knows of another "D" going cheap, please give me a shout!