Heathkit DX-40/DX-100 Modern High Impedance Microphone?

[Garglon]

Can anyone recommend a modern, inexpensive, high impedance microphone that will work with my DX-40 and DX-100 please?

I’ve already bought and sent back a vintage crystal mic that had no output, I’m looking for something new and reliable so I can get on with fixing the rest of the radio without wondering if the mic is at fault!

James
MW0ZAP

[mickm3for]

Hi technofix sell a hi impedence mic Mick

[HamishBoxer]

At £22.99 a good price and cheaper than a Shure 444 of unknown quality. I am sat here also on a DX40 which needs firing up and missing its mic.

[Garglon]

Brilliant, just ordered one from Technofix, thanks!

[Aub]

A couple of guys on the VMARS nets use an Estatic D104. They always sound good. Not sure about availability though.

Hope your new one works well.

Aub

[FrankB]

At the last hamfair here earlier in the month I only saw 1 D104 in over 200 booths. So they are becoming scarce here in the States too.

[G6Tanuki]

The modern equivalent to the old crystal/ceramic mics is the Electret insert; you need to supply it with a bit of bias [9V through a 22K resistor] but the current drawn is minimal and a PP3 will last foir years.

[Radio Wrangler]

Originally Posted by Aub

A couple of guys on the VMARS nets use an Estatic D104.

Astatic? Crystal microphones, very common in amateur service in the fifties and sixties.

https://en.wikipedia.org/wiki/Astati...104_microphone

David

[Aub]

Yes, Astatic. My mistake. I suppose they could be estatic about owning an Astatic 😀

Aub

[M0AFJ, Tim]

Originally Posted by Garglon

Brilliant, just ordered one from Technofix, thanks!

I use one of those on my KW2000A, works a treat

[Silicon]

I am not familiar with the transmitter circuit.

Does the microphone (or signal source) need to be High Impedance?

Would a high output, low impedance microphone work just as well?

Does it need a DC blocking capacitor and/or a high series resistance added?

[Ian - G4JQT]

I too have DX40, DX60 and AT5 transmitters all requiring a crystal mic. But do any of the 'high impedance' mics offered by TechnoFix have the same output level as a crystal mic? It seems unlikely without a matching amp, but has anyone tried?

Thanks.

Ian

[PJay1966]

I’ve got one of those technofix mics going spare if your interested? Bought it for my 101ZD but have since got a Kenwood MC35 which works really well.

[g4aaw pete]

Originally Posted by Ian - G4JQT

I too have DX40, DX60 and AT5 transmitters all requiring a crystal mic. But do any of the 'high impedance' mics offered by TechnoFix have the same output level as a crystal mic? It seems unlikely without a matching amp, but has anyone tried?

Thanks.

Ian

A typical electret element with 1.5 - 3v will work well in place of a crystal mic.
No extra ciruitry required.
I used to use one on a KW Vangard without issue.

[Ian - G4JQT]

Originally Posted by g4aaw pete

A typical electret element with 1.5 - 3v will work well in place of a crystal mic.
No extra ciruitry required.
I used to use one on a KW Vangard without issue.

Thanks for the tip. That's worth trying with an Acos mic case and a couple of button cells. Presumably there's so little drain that a switch isn't necessary.

[g4aaw pete]

If you get the two-connection type of electret element, the voltage source can be inside the transmitter. An isolation capacitor (4.7uF) is then connected from the voltage source point to the AF input of the circuit.

Call me crazy, but I took voltage from the H.T. supply via 150kὨ and put in a string of forward biased diodes (five) to set the voltage to 3v.

[Ian - G4JQT]

Originally Posted by g4aaw pete

If you get the two-connection type of electret element, the voltage source can be inside the transmitter. An isolation capacitor (4.7uF) is then connected from the voltage source point to the AF input of the circuit.

Call me crazy, but I took voltage from the H.T. supply via 150kὨ and put in a string of forward biased diodes (five) to set the voltage to 3v.

What an excellent idea! Looks like with a bit of a redrawing everything can be kept in the tx chassis and keep the two wire plug and wire to the mic.

This sort of thing had crossed my mind, but I didn't bother trying it because I just assumed the output wouldn't be anywhere near as high as that from a crystal mic.

Thanks again.

Ian, G4JQT