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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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24th Mar 2022, 10:06 am | #1 |
Triode
Join Date: Dec 2021
Location: Cardiff, Wales, UK.
Posts: 18
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Heathkit DX-40/DX-100 Modern High Impedance Microphone?
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 |
24th Mar 2022, 11:26 am | #2 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 964
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Re: Heathkit DX-40/DX-100 Modern High Impedence Microphone?
Hi technofix sell a hi impedence mic Mick
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24th Mar 2022, 12:38 pm | #3 |
Dekatron
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 8,935
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
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.
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24th Mar 2022, 2:49 pm | #4 |
Triode
Join Date: Dec 2021
Location: Cardiff, Wales, UK.
Posts: 18
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
Brilliant, just ordered one from Technofix, thanks!
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24th Mar 2022, 5:57 pm | #5 |
Nonode
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 2,039
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
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
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25th Mar 2022, 6:40 am | #6 |
Heptode
Join Date: Oct 2005
Location: Olympia, Washington, USA.
Posts: 664
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
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.
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25th Mar 2022, 10:56 am | #7 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,007
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
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.
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25th Mar 2022, 12:46 pm | #8 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,902
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
Astatic? Crystal microphones, very common in amateur service in the fifties and sixties.
https://en.wikipedia.org/wiki/Astati...104_microphone David
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25th Mar 2022, 5:02 pm | #9 |
Nonode
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 2,039
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
Yes, Astatic. My mistake. I suppose they could be estatic about owning an Astatic 😀
Aub
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26th Mar 2022, 6:56 am | #10 |
Hexode
Join Date: Mar 2006
Location: Helston, Cornwall, UK.
Posts: 304
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
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1st Apr 2022, 11:03 pm | #11 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,169
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
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? |
4th Apr 2022, 12:19 pm | #12 |
Octode
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,326
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
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 |
4th Apr 2022, 5:45 pm | #13 |
Pentode
Join Date: May 2021
Location: Buckinghamshire, UK.
Posts: 133
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
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.
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7th Apr 2022, 6:27 pm | #14 | |
Heptode
Join Date: Jan 2008
Location: Birchington Kent, UK.
Posts: 596
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
Quote:
No extra ciruitry required. I used to use one on a KW Vangard without issue.
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7th Apr 2022, 8:24 pm | #15 | ||
Octode
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,326
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
Quote:
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7th Apr 2022, 9:58 pm | #16 |
Heptode
Join Date: Jan 2008
Location: Birchington Kent, UK.
Posts: 596
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
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.
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8th Apr 2022, 10:17 am | #17 | |
Octode
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,326
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Re: Heathkit DX-40/DX-100 Modern High Impedance Microphone?
Quote:
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 |
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