Dynamic microphones and HT-44
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When I first got my HT-44 running, I was using a high impedance Heathkit microphone and had no trouble achieving full output from the HT-44 with a relatively low mic gain setting (around 3).? When I switched over to the main station microphone, an Inrad M629 dynamic (600 ohm impedance), the best I could do was around 50 watts output with a mic gain setting around 8 on the HT-44.? I also have a Drake T-4XC which has a high impedance input and had the same result with the Drake.? I looked around for a reasonably priced solution and found this:
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It's a model CP8201 inline impedance transformer sold under the ATUS label and manufactured by Audio-Technica.? The primary impedance is 250 ohms and the secondary is 50,000 ohm.? ?Input is a three pin female XLR connector and the output is a 1/4 inch plug.? The price of the device is around $15.? My Inrad mic uses an XLR cable and I installed the device inline at the end of the mic cable and made another short cable to connect to the HT-44.? The matching device solved the problem with using the dynamic mic with the HT-44 and I am able to achieve full output with the mic gain set around 3 on the HT-44, same as with a high impedance mic.? There are many other types of matching transformers available on eBay, most being a bit more expensive than this one.? Another good source of matching devices is Reverb.com, but prices are a bit higher there.
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73, Floyd - K8AC
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The mic amp in the 44 is designed to achieve full power out with 0.005vrms at the mic input. To test the dynamic mic place a 100K resistor across the mic voice line and repeat the words 3, 4, 3, 4. You should read 0.005vrms across the resistor. If you prefer
to use a scope the peak to peak voltage will be 0.0142 or greater.
If your dynamic mic is meeting or exceeding those parameters. Then most likely T2 is misadjusted or there is a fault in the mic amp train.
For more information on the 44 try:
Or: wd0gof.com/hallicrafters-radio/technical-discussions/ht/ht-44/
Walt Cates, WD0GOF
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From: [email protected] <[email protected]> on behalf of Floyd - K8AC <floydsense@...>
Sent: Sunday, August 18, 2024 12:55 PM To: [email protected] <[email protected]> Subject: [HallicraftersRadios] Dynamic microphones and HT-44 ?
When I first got my HT-44 running, I was using a high impedance Heathkit microphone and had no trouble achieving full output from the HT-44 with a relatively low mic gain setting (around 3).? When I switched over to the main station microphone, an Inrad
M629 dynamic (600 ohm impedance), the best I could do was around 50 watts output with a mic gain setting around 8 on the HT-44.? I also have a Drake T-4XC which has a high impedance input and had the same result with the Drake.? I looked around for a reasonably
priced solution and found this:
?
?
It's a model CP8201 inline impedance transformer sold under the ATUS label and manufactured by Audio-Technica.? The primary impedance is 250 ohms and the secondary is 50,000 ohm.? ?Input is a three pin female XLR connector and the output is a 1/4 inch
plug.? The price of the device is around $15.? My Inrad mic uses an XLR cable and I installed the device inline at the end of the mic cable and made another short cable to connect to the HT-44.? The matching device solved the problem with using the dynamic
mic with the HT-44 and I am able to achieve full output with the mic gain set around 3 on the HT-44, same as with a high impedance mic.? There are many other types of matching transformers available on eBay, most being a bit more expensive than this one.?
Another good source of matching devices is Reverb.com, but prices are a bit higher there.
?
73, Floyd - K8AC
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Floyd - K8AC
waltcates