Old RAF type leather helmet - adapting to ICOM type handheld?

[IanLaw]

I have a couple of old RAF type leather helmets, complete with headphones and mask type microphones. These date from anywhere between the later 1940s to early 1950s, I guess. I think the headphones are likely to be the old carbon - & maybe the high impedance - variety, but I have no idea about the mike (inside the old style rubber oxy mask). Unfortunately, I have no suitable technical know-how.

Both helmets are in very good shape - not sure about the electrical bits, yet, but they are externally undamaged.

It used to be possible to buy adapters here in the UK to match these old style helmets to more modern radios, but these commercial adapters are no longer available. I assume these would involve a suitable separate battery supply to deal with any amplification of the weaker output from the modern radio, although this would not be a problem.

Any help in finding either an adapter to suit or perhaps a circuit diagram would be appreciated. I can use a soldering iron OK!

Thanks.

Ian

[1600vw]

Here this may help. This man has done just about everything you can think of. I wish I had just a small amount of his talent.

http://www.bowersflybaby.com/stories...t_options.html

Tony

[rwanttaja]

I have a couple of old RAF type leather helmets, complete with headphones and mask type microphones. These date from anywhere between the later 1940s to early 1950s, I guess. I think the headphones are likely to be the old carbon - & maybe the high impedance - variety, but I have no idea about the mike (inside the old style rubber oxy mask). Unfortunately, I have no suitable technical know-how.

Both helmets are in very good shape - not sure about the electrical bits, yet, but they are externally undamaged.

It used to be possible to buy adapters here in the UK to match these old style helmets to more modern radios, but these commercial adapters are no longer available. I assume these would involve a suitable separate battery supply to deal with any amplification of the weaker output from the modern radio, although this would not be a problem.

Any help in finding either an adapter to suit or perhaps a circuit diagram would be appreciated. I can use a soldering iron OK!

Hi, Ian. Don't know much about the innards of your helmet, and I'm really not an expert, but I'll make a few stabs at it. Let's look at the mike, first.

Back when radios were first being adapted for aircraft, they used what was available...carbon mikes from telephones. So I'm guessing you've got a carbon mike in your face mask. Now, over the past 80 years or so, the INTERFACE standard has remained the carbon mike. You can use an electret mike, a dynamic mike, or whatever with your aircraft radio, but the maker of the microphone must ensure it meets that old 1930s carbon mike standard!

In short, I think a '30s carbon mike would work on an aircraft radio without modification, and with little chance of harm. I'd just give it a try.

Whether it still works.... Hmm. Carbon mikes work by sound waves pressing on carbon powder. If the carbon powder gets compacted or solidifies, the mike won't work. Back in the day, we were taught to whack the microphone against something if it didn't seem to work...to shake up the carbon particles. Not sure you'll want to do THAT to your valuable antique.

But I don't think it'll hurt just to hook it up and give it a try. Note that aircraft mike plugs are not standard, they're about 0.20" diameter. They were originally used on...yes, you guessed it, telephones (actually, telephone switchboards). They're three conductor, and, IIRC, the microphone wires go to the main shaft and the middle ring, and the tip is used with the push-to-talk switch (short the tip to ground to transmit).

As far as the headphone speakers, aviation headsets are also stuck with the standards of the '30s, and I'm guessing that the ones in your helmet are probably ~300 ohm impedance, just like standard headsets. They might be low impedance, around 8 ohms like modern ear buds, in which case they probably won't be loud enough.

In actuality, you probably won't want to use the microphone that's built into the mask...looks cool, but I think it'd be irritating to wear for any length of time unless you have to be on oxygen. You might consider building a slim-line microphone holder that'll fit under the helmet... I show how, here:

http://www.bowersflybaby.com/tech/h_headset.html

[Edit] Going through what you posted again, it looks like your major issue would be the mechanical adaptation of the existing plugs, rather than the physical hookup of the microphone and speaker. Could you post a photo of the plug?

Also, the ICOM radio will have a 8 ohm speaker output...which will work with the aircraft-style 300 ohm speakers (I used my Flightcom during the winter) but may not be loud enough. There's a small audio output transformer that can be used to match an 8-ohm headset to the aircraft 300-ohm output. This would just be the same thing in reverse...but I've never tested it that way. Instructions are at the bottom of:

http://www.bowersflybaby.com/stories/helmet2.html

Ron Wanttaja

[rwanttaja]

Going through what you posted again, it looks like your major issue would be the mechanical adaptation of the existing plugs, rather than the physical hookup of the microphone and speaker. Could you post a photo of the plug?

Ian...does this picture show your plug?

Also, researching online seems to indicate that Headset Services at Shoreham might be able to help you.



Ron Wanttaja

[IanLaw]

That's brilliant Ron ( & thanks 1600VW) and is exactly what I was looking for. Very grateful for all your advice and information, again.

I'll print everything off and read it carefully! The jack plug in your photo is exactly like mine. Unfortunately, I have been in touch with Headset Services at Shoreham and they have discontinued their adapter. Rats... But I think they may have the plug adapter I will need.

This will give me something to occupy my time while I get over my recent "Gall" stone op. and stop me getting bored with sitting around indoors!

Thanks once again.

Ian

[rwanttaja]

That's brilliant Ron ( & thanks 1600VW) and is exactly what I was looking for. Very grateful for all your advice and information, again.

As most of the folks in this group can attest, getting me to respond is not difficult. Getting me to shut UP, on the other hand....

And let me demonstrate by adding a few more thoughts.

Thanks for asking this question, as while I have a book or two on flight helmets, I've never really considered the electrical connections used. The bit of research I did was interesting.

Anyway, it sound like your helmet probably has the RAF plug, which is very similar to the modern-day NATO plug used on modern helmets. A lot of companies still, apparently, sell adaptors for the NATO helmets to be used on GA radios.

Unfortunately, it sounds like the compatibility is not quite there...one source said you could plug a NATO headset into an RAF jack, but that an RAF plug won't stay in a NATO jack. Which kind of eliminates the potential to use a NATO adaptor (though a bit 'o tape might hold them together).

Besides, them NATO adaptors are pricey.

What you might consider is switching plugs. Military equipment like this is made to be maintained, so unscrewing the shell of the RAF plug probably will expose the connections to the jack...which might even be screw terminals, which would make disconnection rather easy. I'm guessing the NATO plug would be the same way, so the switchover would be relatively easy and you could change back if you ever wanted to restore the helmet to original condition. Or you might consider building an interface inside a small electronics-project box or pill bottle.

Before you do that, though, check and see if your headset will work with the ICOM. Like I mentioned a post or two back, the ICOM has an 8-ohm speaker output, which is not really compatible with the "classic" 300-ohm headset. Use some clip leads (insulated wires with alligator clips) and make a temporary connection to the headset speakers to either your ICOM or any consumer audio device, and see if (a) it works at all, and (b) whether it'd be loud enough to hear in an airplane.

The problem is, these old helmets are not made for noise attenuation. They put big speakers atop your ears, driven by vacuum-tube radios with 100+ volts available to push sufficient sound energy to the pilot's ears. Also it's another warning that the helmet speakers may not work with the puny 12V aircraft avionics; they're fairly low efficiency since there'd be a lot of power to push across them, 70 years ago.

As I get older, I'm getting more sensitive to hearing loss. I used to fly my 150 without a headset, and cringe at the thought of what it did to my hearing. There are a lot of deaf pilots out there, and I really recommend good passive noise attenuation in a headset. Particularly if it's being flown in a open-cockpit plane. I bought one of those Russian helmets and converted it use in my Fly Baby, but the noise level was HIGH. Finally fixed it by switching to an ear bud, instead of just the speakers.

Now, the last suggestion: you've got a real collector's item there. Why risk damaging it by wearing it? Why risk getting it stolen when you fly somewhere else. The fact that they no longer sell adaptors is a good sign that these are getting rare. Set it reverently with your lares and penates, and find a more modern alternative.

Pop's Leather does custom flying helmets for a surprisingly low cost:

http://www.popsleather.com/new_catal...abec-130762415

I haven't bought from them...yet...but I hear a lot of good things. The helmets are custom-made, and the cost is about half what an adaptor would be (if you could find one). I posted the link above, on how to build a slimline headset that'll fit under the helmet.

You might even be able to adapt the mask-type microphone to the new helmet, giving you much of the look without risking a lot of delicate old leather. With a set of RAF goggles, most folks wouldn't be able to tell the difference from ~20-30 feet away.

Just a thought....

Ron Wanttaja

[IanLaw]

Many thanks again Ron - that sounds like good advice and I'll look into all that you suggest, before attempting to adapt my old helmet(s). I bought both helmets about 50(!) years ago, I guess, in an old "Army & Navy" store, probably for the equivalent of a few Dollars.

This will be an interesting project for me and I'm looking forward to having a go, if I decide to try to adapt just one helmet.

Ian

[dsbrantjr]

Many thanks again Ron - that sounds like good advice and I'll look into all that you suggest, before attempting to adapt my old helmet(s). I bought both helmets about 50(!) years ago, I guess, in an old "Army & Navy" store, probably for the equivalent of a few Dollars.

This will be an interesting project for me and I'm looking forward to having a go, if I decide to try to adapt just one helmet.

Ian

Ian: The plug you need for your mic is a 0.206" diameter PJ068 type - they are sold by many outlets including Aircraft Spruce: http://www.aircraftspruce.com/catalo...paneljacks.php

The headphone plug is a PJ-055 which is the standard 1/4 inch "phone" plug. Widely available.

I would not worry too much about driving a 300 Ohm headset with a low-impedance source; I use my 600 Ohm AKG K240 stereo phones on a computer sound card intended for 32 Ohm 'phones all the time and they work fine. If you are low in volume a 8 to 600 Ohm transformer available (used to be!) at Radio Shack will work fine. But I bet you won't need it. Driving a low impedance load with a high-impedance source is where you run into trouble.

[rwanttaja]

Ian: The plug you need for your mic is a 0.206" diameter PJ068 type - they are sold by many outlets including Aircraft Spruce: http://www.aircraftspruce.com/catalo...paneljacks.php

The headphone plug is a PJ-055 which is the standard 1/4 inch "phone" plug. Widely available.

That's *if* he wants to cut off the original plug, which I wouldn't recommend on this antique helmet. But if he replaced the existing plug with the almost-identical NATO one, he could use existing NATO to GA converters.

BTW, as I mentioned a while back, the standard for headsets of that era were driven by telephone technology of the 20s/30s. The mike plug is a good example, since it was the same one used on switchboards (with the 1/4" plug used for the speaker portion). Aviation is, in fact, the only remaining user of the 0.206" plug.....

I would not worry too much about driving a 300 Ohm headset with a low-impedance source; I use my 600 Ohm AKG K240 stereo phones on a computer sound card intended for 32 Ohm 'phones all the time and they work fine. If you are low in volume a 8 to 600 Ohm transformer available (used to be!) at Radio Shack will work fine. But I bet you won't need it. Driving a low impedance load with a high-impedance source is where you run into trouble.

I have an ICOM handheld (8-ohm output impedance) permanently mounted in my panel (at least as permanent as anything is, in my airplane) and use a Flightcom Denali ANL headset (300 ohm impedance) during the cold months. The volume is OK, but always wish I had a few more degrees left on the volume control.

Now, my Fly Baby is a loud SOB...105 dB at chest level. It may be fine for guys with closed-cabin airplanes.

When it gets warm enough, I switch to a set of 8 ohm ear buds, and have to really back off on the volume control. It's painfully loud, at the full setting.

I tried the Radio Shack transformer (PN 273-1380) in the step-up mode to see if it'd make my ANL headset a bit louder, but it didn't seem to boost the audio power. May fiddle with it some more. One possibility that that my little handheld just doesn't have the oooomph to make those high-impedance speakers really shake. It's only half a watt, with or without the transformer. The panel-mounted ICOM A200 can shove almost ten times the audio energy into your ears (4 watts).

The Rat Shack transformer does work well for running ear buds on conventional aircraft radios (e.g., those expecting 300 ohms). Most stores seem to have the transformers in stock, and I've ordered them online as well. But they seem to be a bit tougher for our European friends to find. I ended up sending a couple to a Dutch friend with a Fly Baby.

Ron Wanttaja

[Ernie]

Can't help with the headset, but I have several helmets from Pops Leather. Make sure you describe exactly what you want because they will send exactly what you order. I am very happy with everything I've ordered from them.