The AM Forum

Excuse me for posting several separate questions, but it seemed easier to split them up by topic. I'm currently putting together a Heathkit vintage boat anchor station for my first HF work since 1970 - when I built my first transmitter, 2 tubes, code 25 watts input, when I was 12!

I have gathered all the matching components for a DX-60, HR-10, plus matching VFO, SWR, etc for this fun set up. I need a high impedance mic for this transmitter. I'm not opposed to buying something new, as my experience with vintage mics of this nature generally lead to troubles.

Anyone using or have experience/opinion with the Heil GMV, or Gold Standard "Vintage" version, that is hi impedance? Seems a bit fancy, and I obviously won't be needing the PTT feature.  What's out there that is good? I don't mind spending some $$ for a good mic, as I intend to move up tp much better AM gear over the coming year. But I have this outfit to get started with right now.

Thoughts?

Tim in Bovey

Astatic made this thing called a D-104 for years.

Megohm input impedance, hi fi, if terminated in it's characteristic impedance, good sensitivity, and literally, MILLIONS of them out there.


Sorry, had my sarcasm switch on.

IOW, the D104 is a damn fine mic.  I use one, hifi setup, and NOBODY knows the thing isn't a multi hunnerd dollar mickey-fone.

--Shane

I'm actually with Shane on this.  I have the Heil Vintage you mentioned.  It is relatively low output.  At least for my voice, it takes quite a bit of equalization to sound good.  The D-104, however, is just a great microphone.

If you end up with the very common amplified D-104 you'll have to tweak it to get the lows back in.  The easiest mod is to just put a resistor in series with the mic element.  I can't remember the value but somebody on this board does.  Or you could just bypass the amp altogether.

Agreed, but consider two things.  (1) For high impedance input, discard that CB "power mic" crap in the base of the mic, if it has it.  (2)  You need a bare minimum of 5 megohms of terminating resistance on the crystal element, according to Astatic.  I use 10 megohms on mine.  The terminating resistance should be the grid leak of the high-impedance first stage.  A one-megohm load on the D-104 crystal element will make it sound like a tin-can telephone.  The mic is capable of good low frequencies in the voice range, but you need to work it into a high resistance load.

I am working on an experimental push-pull input stage for mine, and with that I'll be able to run it into a 20 megohm load.

They are right.  You can't beat the D-104.  Just don't get the element too warm or humid; they tend to die.

Mitch

I've actually been looking at some D-104's.  The best bet would be to find one without the amplified base? My concern, mostly, was that so many of them have dead or weak elements in them. I see tons of the amplified models around, but the standard ones every now and then too. Odds I'll get a dud? From what I've read recently replacement elements are a bit of a crap shoot.

Tim in Bovey

You can't get new crystal elements any more.  Astatic quit making them.  It's no problem to disconnect that CB trash in the base, and run the crystal element directly to the mic cord.

Like any hamfest "bargain", the condition of the crystal will be a crap-shoot.  You might be able to measure the output with a sensitive digital multimeter, using the ac millivolt range.  I'll try and see how well that works with mine.  Sometimes D-104's are cheap enough that you could afford to pick up two or three of them to make it more likely that at least one is good.

My son's wife's grandfather gave me an old D-104 he'd had in his workshop for years.  It was in poor shape with some of the stuff missing from it, but I took it home and checked out the element, which was still good, so I now have a spare for mine.

Another way to get an idea if the crystal is still good is to hold the mic in transmit position if it is equipped with a push-to-talk switch,  or otherwise just test the mic as is.  Make good contact with the grounded part of  the mic case using your hand, put the mic up to your ear, and touch the "hot" output terminal of the mic plug to a massive metal object like a bare metal spot on a car, or if indoors the screw that holds a light switch cover in place, or maybe the metal handle on a bathroom spigot.  If you hear a faint click from the mic element, the crystal should be good.

Of course,  someone may have replaced the element with some cheap non-standard one, or some Hammy Hambone type could have pierced a dozen holes in the diaphragm like they did on one of mine, but chances are if the click test is positive, the mic is good.  BTW this works only with the original unamplified version; it will not work with the "power mike" attachment in place.

I've used my Lafayette Crystal Lapel mike, bought in 1958 for $1.95, on my Apache. I just tried the mike several months ago and it still worked fine. These things pop up at flea markets all the time.

You never know what might work.   For my AF-67, of all my microphones, a crystal mike from an old Genave 2M-FM transceiver works the best.

D104 astatic non powered version
sure 444
EV 638
EV 634

Just about any of the old Electro voice, astatic or sure high impedance mics will work with the radio. What sound you like is up to you. I would just find an old D104.

Clark