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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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Old 26th Aug 2020, 1:22 pm   #21
Radio Wrangler
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Default Re: Codar AT5 TX

You can getta lotta volts out of a carbon microphone, competing with crystal microphones.

Otherwise you need some amplification.

But the carbon mike still needs DC power and the quality is not good. Used to be common in simple AM transmitters.

Davi
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Old 26th Aug 2020, 4:09 pm   #22
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Default Re: Codar AT5 TX

Crystal mics were no good in the car, a brief encounter with some sunshine would ruin them. The ideal mic for the AT5 I found to be the Shure 201 ceramic which seemed unaffected by heat yet had high impedance for the valve modulator. They do come up from time to time on that err popular Internet auction site.
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Old 31st Aug 2020, 4:33 pm   #23
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Default Re: Codar AT5 TX

As it happens just 'won' a shure 201 on said site for my AT5 / DX100 homebrew tx.

It'll be interesting to hear how is sounds compared to the eletret mic I'm using at present.
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Old 31st Aug 2020, 5:35 pm   #24
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Default Re: Codar AT5 TX

DX100 homebrew. Is that a clone of the Heathkit one?

Love to see that

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Old 31st Aug 2020, 5:54 pm   #25
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Default Re: Codar AT5 TX

I started of wanting to build an AT5 with a bit more punch and to cover 60mtrs as well as 160 and 80 mtrs - so the project evolved into an AT5 on steroids ultimately using a pair of KT88's, Woden UM2 mod tranny and a pair of 6146's in the final.

The design was a hybrid of a RSGB article mid 60's combined with a DX100 - trying to take the best bits from both of them.

If you search for some of my earlier posts you'll see photo's of it.

Here's one such thread
https://www.vintage-radio.net/forum/...d.php?t=152370

and another

https://www.vintage-radio.net/forum/...ight=g4wim_tim

On air reports have been good but always thought it could benefit from an old style crystal mic - time will tell !

edit - apologies for thread drift off topic.
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Old 31st Aug 2020, 7:59 pm   #26
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Default Re: Codar AT5 TX

Thanks for that. It looks great. I'll have to come on 3.615 more often with my homebrew.

73

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Old 20th Feb 2021, 9:22 pm   #27
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Default Re: Codar AT5 TX

Hi all. Been reading about you microphone problems. I was wondering if an old insert from a old type of telephone would work?
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Old 20th Feb 2021, 10:11 pm   #28
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Default Re: Codar AT5 TX

Old telephones used a carbon microphone (variable resistance). You'll need to supply a couple of volts to pass some current through it. If you pass this through the low impedance primary of a step-up transformer you'll get plenty of audio on the secondary.
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