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Old 13th Sep 2018, 9:57 pm   #1
GSBX1220
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Default Telephone style microphone ID req

Hi folks

I have a telephone style microphone that is in fantastic condition. I found it in a box of bits in the loft. I think it's a Pye unit. Does anyone know what type of microphone insert it has in it? It also has a 6pin connector on it.
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Old 13th Sep 2018, 10:23 pm   #2
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Default Re: Telephone style microphone ID req

That looks like Pye Whitehall or very close.
Both inserts by A.P.Besson most likely.

The Red/White striped one in the Mic is almost certainly same as Westminster AM series, Green White is more or less same as Telephone Earpiece ex a GPO Telling-Bone handset.

If you want to use that Mic insert for FM, use it as it is, or if a bit harsh sounding then put 100n across it.
Worked for me.

PS. The plug is not original... but expect you knew that already
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Old 13th Sep 2018, 10:23 pm   #3
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Default Re: Telephone style microphone ID req

Well, that's a NATO stock number on the back- might lead somewhere.

Poke it with a DMM and see if it's resistive. If it is, it'll be dynamic, if it's open circuit, probably crystal. Either way it should click when prodded.

Can you look at it with a 'scope?
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Old 13th Sep 2018, 10:42 pm   #4
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Default Re: Telephone style microphone ID req

Hi

Yes, I did poke it with a meter & it is resistive. 47 ohms. There is also an electrolytic capacitor in series with it For some reason.
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Old 13th Sep 2018, 10:42 pm   #5
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Default Re: Telephone style microphone ID req

Just spotted it has a curious electrolytic added - for sure not original.

Probably means it has been modified to work with something that sends a polarising Voltage to an electret + preamp.

No Pye Whitehall ever needed that - goes well with the Jap mic connector though.
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Old 14th Sep 2018, 6:02 am   #6
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Default Re: Telephone style microphone ID req

Quote:
Originally Posted by GSBX1220 View Post
I think it's a Pye unit. Does anyone know what type of microphone insert it has in it? It also has a 6pin connector on it.
My notes on this type of insert say Red with White Flash: 300 Ohm microphone, presumably dynamic. Green with White Flash: 300 Ohm earpiece.

Cheers

Roger

Last edited by G3VKM_Roger; 14th Sep 2018 at 6:04 am. Reason: add
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Old 14th Sep 2018, 8:27 am   #7
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Default Re: Telephone style microphone ID req

The style and inserts are standard Larkspur although they were green not black. The plug of course isn't military.
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Old 14th Sep 2018, 12:04 pm   #8
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Default Re: Telephone style microphone ID req

Resistive 47R sounds about right for nominal 300R impedance.....
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Old 14th Sep 2018, 2:40 pm   #9
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Default Re: Telephone style microphone ID req

Pye PMR mics often had a plain aluminium colour insert with impedance of 2400 ohms.
FM had 3 tiny holes, AM more larger holes like in your red/white example.
However, just to confuse, early fm also had several of the larger holes as well. They were sought after for amateur use rather than the 3 hole ones. Maybe someone remembers their part number?
I think AM had "M4BZ2400" printed on the back.
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Old 14th Sep 2018, 2:44 pm   #10
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Default Re: Telephone style microphone ID req

Quote:
Originally Posted by GSBX1220 View Post
There is also an electrolytic capacitor in series with it For some reason.
D.C. blocker? It'll be a 'rocking-armature' unit (higher Z than the receiver rocking-armature unit) and stands to be polarised beyond use if there's a constant direct current through it.
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Old 14th Sep 2018, 2:57 pm   #11
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Default Re: Telephone style microphone ID req

You may find this useful:-
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Old 14th Sep 2018, 10:28 pm   #12
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Default Re: Telephone style microphone ID req

I may be wrong but I think the Marconi RC690 might have used that combination of plugs and handsets in Police vehicles. The Whitehalls used a square multi pin affair (Jones plug?) which went into the back of the control head. As far as I remember I think the Whitehall may have had a balanced mic input circuit.
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Old 15th Sep 2018, 2:37 pm   #13
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Default Re: Telephone style microphone ID req

The handset itself looks very similar to the ones used with the HF RACAL TRA931 (Syncal30) and the TRA967 low-band VHF manpack (though the plug is obviously non-standard).

Note that the wiring of the audio-gear on these RACALs, though using a 'Clansman audio' type plug, is different to the Clansman wiring. Guess who found this out the hard way?
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Old 15th Sep 2018, 7:17 pm   #14
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Default Re: Telephone style microphone ID req

It's the same handset as used on the former MOULD radio transceivers too.
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Old 15th Sep 2018, 10:59 pm   #15
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Default Re: Telephone style microphone ID req

I think the handsets used on the Police / Fire RC690s (etc) were similar but with a PREH-type plug, which was fully shielded (no plastic bit sticking out at the end). Also think the Westminster-series mic plugs were the same...? Some earlier sets (Whitehall, Vanguard, Cambridge etc) used the larger 6-pin Painton plug. Same audio inserts though. Didn't the Mould Pegasus use an Amphenol handset connector, similar to the Clansman-type? If the connector on the handset in the photo has a screw-up securing ring, rather than a bayonet type, it looks like it would mate with the socket type on an amateur-type radio.

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Old 16th Sep 2018, 8:41 am   #16
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Default Re: Telephone style microphone ID req

Quote:
Originally Posted by Sparky67 View Post
Didn't the Mould Pegasus use an Amphenol handset connector, similar to the Clansman-type? If the connector on the handset in the photo has a screw-up securing ring, rather than a bayonet type, it looks like it would mate with the socket type on an amateur-type radio.
As I recall, yes. But the handset in the O/P picture is fitted with what looks like a plug for an amateur transceiver or CB radio. Been modded, maybe?
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Old 16th Sep 2018, 9:16 am   #17
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Default Re: Telephone style microphone ID req

It’s certainly a possibility... It could also have been used with an amateur / commercial HF radio adopted for use by the military perhaps. The RAF used a number of re-badged different Icom HF radios. Or somethin else completely different! Just due to numbers it’s likely to be a (modified) ex-Police or Fire Service handset, they used thousands of these S G Brown (later Racal Acoustics) handsets. Unless the OP has more info I guess we will never really know...!
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Old 17th Sep 2018, 8:09 am   #18
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Default Re: Telephone style microphone ID req

This looks like the handset used with the Ptarmigan communications system. The handset is a little larger than the similar tactical handset used with the Larkspur range of systems and many others. The inserts are the standard dynamic type manufactured originally by STC. Red/White is the transmitter (microphone) and Green/White is the receiver (earphone) There is also a Red/Black which is a carbon mic. The dynamic inserts are nominally 300ohm impedance. These handsets were manufactured by Racal Acoustics, who bought S.G.Brown, the original manufacturers. The plug is not original.
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Old 17th Sep 2018, 9:29 pm   #19
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Default Re: Telephone style microphone ID req

Hi

The connector is the 6pin type found on some amateur gear. The microphone seems to be wired in a balanced configuration with the white and green wires being individually shielded.

I have since first posting this, I have re terminated the plug and used it on 2M SSB. I was told it sounds rather toppy and lacks lower frequencies.
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Old 17th Sep 2018, 11:11 pm   #20
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Default Re: Telephone style microphone ID req

A mike designed for professional communications work is unlikely to have much output outside the 300-3000Hz range. Putting signal energy into low audio frequencies doesn't improve intelligibility and just wastes transmitter power. If you want the audio to sound good, use a suitable mike.
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