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Old 16th Feb 2018, 10:54 pm   #1
Sparks
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Default Amplivox Astrolite headset

A while back I bought a few used examples of this headset. Externally they seemed fairly run of the mill but the microphones and earphones were a bit odd; the microphones had an impedance of just 25 ohms and the earphone elements were a very high 6000 ohms each. All of the moving iron variety. Does anyone have a clue as to the likely application of these units ?

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Old 17th Feb 2018, 1:25 am   #2
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Default Re: Amplivox Astrolite headset

Carbon mics were commonly used in avionic installations, this mic may be a direct replacement?
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Old 17th Feb 2018, 3:55 am   #3
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Default Re: Amplivox Astrolite headset

Aviation headsets were available with a variety of optional earpiece and microphone types. At that impedance you could either have a carbon mike or a moving coil one.

Rather than risk shoving a lot of DC current into a moving coil transducer, Try the microphone into a sensitive amplifier. If you get audio, it's a moving coil mike, if not, then try a carbon mike bias circuit.

It is also possibly a dual microphone arranged for noise cancellation, whatever type they may be.

Nowadays, even with vintage aircraft, there seem to be very few carbon mikes in use. Most powered aircraft have radios set up for electret microphones. Glider pilots with their quiet cockpits love 'dynamic' mikes on goosenecks and loudspeakers in place of headphones. The electret mikes are usually 'phantom' powered by DC supplied backwards down their cable from the radio.

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Old 17th Feb 2018, 10:22 am   #4
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Default Re: Amplivox Astrolite headset

Quote:
Originally Posted by AC/HL View Post
Carbon mics were commonly used in avionic installations
I never knew that! Every day is a learning day.

Perhaps you could tell if it's a carbon mic by shaking it gently or repositioning it and seeing if the resistance changes? A carbon granule telephone inset mic No:13, for example, will change typically from between 200 Ohm - 1.8 kilohm.
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Old 17th Feb 2018, 11:15 am   #5
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Default Re: Amplivox Astrolite headset

I'm familiar with both types of transducer. The earphone is a rocking armature type and the microphone is a noise-cancelling, tropicalised magnetic type. Definitely not moving coil, carbon or electret. The usual impedance for both the earphone and microphone is 300 ohms. Here are some photos.
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Old 17th Feb 2018, 8:30 pm   #6
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Default Re: Amplivox Astrolite headset

Interesting variant. These Astrolite headsets date from circa 1969 onwards, were used often in aviation, broadcasting /TV talkback, and I have several which go with my vintage language laboratories, 200 ohms I think both mic and 'phones. Terminated in Nexus TP120 plugs or 5- pin DIN. I usually buy them when I see them cheap if the spec matches, as I can always use them. I also have a pair which are just 'phones, rebadged Bell and Howell.

They are prone to a few problems now with age. The ear cushions tend to go rock hard and crack, the internal boom mic cable can go intermittent, the rubber bungs on the earpiece sliders can also deteriorate, and I had one where the actual plastic mount for the earpiece slider broke. They can usually be easily repaired.
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Old 18th Feb 2018, 1:31 pm   #7
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Default Re: Amplivox Astrolite headset

This thread piqued my interest, so I ratched out my 'as-new' Clement Clarke Airlite 62 Airmed headset, which is fitted with a rather fat 8-pin Cannon socket, bringing out each receiver (nominally 40 Ohms) and the dynamic mic (nominally 300 Ohms).

My questions to the aviators are:-

Why the need for binaural connections? In use, does each receiver take a different source? On the odd occasions I've flown in a light aircraft and gyrocopter, I've never noticed this.

Were carbon mics used for robustness and simplicity? My set is dynamic, insofar as it clicks when an AVO is applied on 'Ohms' but not sure if it's noise-cancelling or not.

I appreciate that similar headsets would be configured for different functons. Mine are ex-MoD and have a NATO number.
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Old 18th Feb 2018, 1:35 pm   #8
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Default Re: Amplivox Astrolite headset

They are usually very robust units if they're looked after. Wrapping the main cable around the set tends to stretch the earshell sliders, causing the rubber to weaken and perish. I've owned several over the years and have yet to encounter a faulty microphone. I've had one or two duff earphones.

I like the Astrolite; it's very versatile and comfortable if a bit fiddly to repair. Stupidly expensive as well when brand new. Shame they're no longer made.

I tried one of these 25 ohm microphones with a Sanyo cassette recorder. Not much good I'm afraid. You almost have to shout to record your voice, unlike the standard 300 ohm version. The 25 ohm mikes must have been designed for a very specific purpose.
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Old 18th Feb 2018, 3:06 pm   #9
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Default Re: Amplivox Astrolite headset

Russell. I'm no expert but it sounds like your Airlite 62 is an ex-Royal Navy example. If so it will have a 300 ohm NC moving coil microphone and two 300 ohm rocking armature earphones, most likely parallel wired. Definitely not for civil aircraft use.

As for carbon mikes in aircraft, I really don't know. The radios on some early British civil airliners, such as the Viscount and Trident, were designed to take simple electromagnetic or moving coil microphones. Again, around about 300 ohms compared to the 100 ohms of a carbon mike. Earphones wired in either series or parallel, never separately wired as far as I know. The twin plugs for mike and earphones is another question I can't answer, I'm afraid ! The four-pole brass NATO AM671 plug used to be common in British military aircraft and some civilian machines such as the BAC 1-11 and the BAe ATP.

By the way, noise cancelling mikes generally have sound holes on both sides of the casing. That's how I spot them.
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Old 18th Feb 2018, 3:25 pm   #10
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Default Re: Amplivox Astrolite headset

Civilian light aircraft often use twin jack plugs, the mike is the unusual smaller diameter one, the headphone is the more common 1/4 inch one.

The original poster's photo isn't an Airlite 62. Have a look at the photo Ben posted.

Here's what an Airlite 62 looks like:


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Old 18th Feb 2018, 3:35 pm   #11
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Default Re: Amplivox Astrolite headset

Quote:
Originally Posted by russell_w_b View Post
Were carbon mics used for robustness and simplicity?
Yes, they're also usefully high output so less RF susceptible audio gain neeeded in the comms system.
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Old 18th Feb 2018, 7:26 pm   #12
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Default Re: Amplivox Astrolite headset

Quote:
Originally Posted by Sparks View Post
Russell. I'm no expert but it sounds like your Airlite 62 is an ex-Royal Navy example. If so it will have a 300 ohm NC moving coil microphone and two 300 ohm rocking armature earphones, most likely parallel wired. Definitely not for civil aircraft use.
My set could be indeed for non-aviator use; nothing more than an intercom talk-back system (for example). They may be RN as you suggest. But the receivers are definitely 40 Ohms. They're the standard green A.P.Besson rocking armature units.

Quote:
Originally Posted by Sparks View Post
Earphones wired in either series or parallel, never separately wired as far as I know
Mine definitely come out as separate pins: 1&2 for the mic; 3&4 one receiver; 5&6 for the other receiver. I needn't hi-jack the thread any further by putting a pic of the Cannon plug on (sorry, David! ). It was on the strength of that that I looked up the headset and there were various things about mono and binaural. I guess it allows optimium flexibility with the series or parallel - or separate - configuration made in the equipment, rther than the headset.

Quote:
Originally Posted by Sparks View Post
By the way, noise cancelling mikes generally have sound holes on both sides of the casing. That's how I spot them.
Mine could be noise-cancelling, then. I had a similar headset nearly forty years ago when I was first licenced and used it on my TR7200G with a separate PTT switch. I looked a bit of a wally driving round with it on so it was back to the fist-mic after that.

Quote:
Originally Posted by Radio Wrangler View Post
Civilian light aircraft often use twin jack plugs, the mike is the unusual smaller diameter one, the headphone is the more common 1/4 inch one.
Those are how I've seen them in aircraft, David: BPO 'B'-gauge big one and a BPO 'Bantam' smaller one?
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Old 18th Feb 2018, 8:27 pm   #13
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Default Re: Amplivox Astrolite headset

The microphone plug on a twin plug aviation headset is unique to aviation AFAIK. The diameter is slightly less than a 1/4" but greater than the BPO Bantam.

40 ohm receivers suggest a noisy environment. I doubt the 6000 ohm units I have would be much use if that were the case.

BTW Astrolite production ended about twelve years ago. The Airlite 62 predates the Astrolite and is still available.
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Old 20th Feb 2018, 9:12 am   #14
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Default Re: Amplivox Astrolite headset

I also have a Unilite 62 (single earphone), a few Airlite 71s and a single earphone Astrolite. The 71 is essentially a lightweight, more streamlined 62. Very comfortable but like the Astrolite, no longer made. A pity.
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Old 20th Feb 2018, 10:05 am   #15
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Default Re: Amplivox Astrolite headset

I seem to remember the first set of Airlite 62s I had being badged up as Racal Amplivox. Ex-RAF 14MU, Carlisle and courtesy of John's Radio, Bradford, in exchange for some telephone magnetos.
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Old 24th Feb 2018, 12:16 pm   #16
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Default Re: Amplivox Astrolite headset

These Astrolites with the non-standard impedance also had very clunky green MIL-spec Cannon connectors fitted. So they were probably used in tanks or submarines or something else with a defensive capability.
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Old 25th Feb 2018, 2:57 pm   #17
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Default Re: Amplivox Astrolite headset

Quote:
Originally Posted by ben View Post
These Astrolite headsets date from circa 1969 onwards, ... I have several which go with my vintage language laboratories,
I "liberated" a few from the school language lab which was being dismantled, which was based on reel-to-reel tape machines.
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Old 25th Feb 2018, 3:43 pm   #18
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Default Re: Amplivox Astrolite headset

We also had Astrolites for our Tandberg language lab at high school circa 1985. Dynamic microphones and TP120 connectors which gave a solid, high quality connection. I think this is what stimulated my interest, plus the fact they were also used in my local airport control tower.
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Old 25th Apr 2018, 11:20 pm   #19
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Default Re: Amplivox Astrolite headset

Here is some information that might prove useful for anyone with these trusty old workhorses. Today some replacement pads arrived which I had ordered (type SONY MDR7506 OR V-6) and I was pleased to find that they fit very well.

They are nowhere near as robust as the original grey pads, but they only cost about a pound including postage, so quite a bargain. Should be fine for occasional light use and it means the headset is usable once more - the originals had gone rock hard and cracked (I suspect they were hanging in a language lab booth near a classroom window for about 15 years).

I have my eye on some leather ones costing a couple of quid more which i may also buy - watch this space!
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Old 26th Apr 2018, 7:11 pm   #20
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Default Re: Amplivox Astrolite headset

Thankyou for the information Ben. The Sony pads look okay and are a change from grey. It will be interesting to see how the leather pads stack up.
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