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 Post subject: SCR-274-N command set and T-17 microphone woes
PostPosted: Feb Tue 05, 2019 3:00 am 
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Joined: Mar Fri 29, 2013 4:46 am
Posts: 178
Location: Livermore, CA
I have a SCR-274-N command setup with a BC-456 modulator, and T-17 mic. Of course the T-17 is dead well almost dead anyway I've heard that an electret element can be swapped out in place of the stock carbon mic has anyone tried this, and which element did you use?

Dave


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 Post subject: Re: SCR-274-N command set and T-17 microphone woes
PostPosted: Feb Tue 05, 2019 4:00 pm 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 7312
Location: Mountains of Mourne. Ireland.
Hello Dave,

The T-1 handset microphone element from an old telephone is recommend here for use with RM-12!
http://amfone.net/Amforum/index.php?top ... #msg269223

Not sure if this would suit your setup... :shock:

NOS: https://www.ebay.com/itm/153331168277
Lots more on ebay.


:) Greg.

oh... here is a bit of major surgery to make a T-5 fit.
http://k4che.com/T-17/T-17.htm

Wear eye-protection. Lol


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 Post subject: Re: SCR-274-N command set and T-17 microphone woes
PostPosted: Feb Wed 06, 2019 12:37 am 
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Joined: Mar Fri 29, 2013 4:46 am
Posts: 178
Location: Livermore, CA
egg wrote:
Hello Dave,

The T-1 handset microphone element from an old telephone is recommend here for use with RM-12!
http://amfone.net/Amforum/index.php?top ... #msg269223

Not sure if this would suit your setup... :shock:

NOS: https://www.ebay.com/itm/153331168277
Lots more on ebay.


:) Greg.

oh... here is a bit of major surgery to make a T-5 fit.
http://k4che.com/T-17/T-17.htm

I was thinking of using a microphone element from an old telephone handset wasn't sure what vintage telephone handset I need to look for 60's or 70's?

Dave

Wear eye-protection. Lol


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 Post subject: Re: SCR-274-N command set and T-17 microphone woes
PostPosted: Feb Wed 06, 2019 2:42 pm 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 1315
Location: Santa Rosa, CA
Nice setup Dave! Sometimes the carbon particles in the mic
element get packed and a good whack will loosen them up.
Nothing to loose. Is the mic getting the right bias?
Steve

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 Post subject: Re: SCR-274-N command set and T-17 microphone woes
PostPosted: Feb Wed 06, 2019 7:07 pm 
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Joined: May Fri 01, 2015 2:33 am
Posts: 1286
Location: Roslyn,Pa 19001
Used a couple of T-17 on my TBS-50 a few years back. Worked fine as is.
https://www.flickr.com/photos/42774321@N08/3939067236/

Terry N3GTE


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 Post subject: Re: SCR-274-N command set and T-17 microphone woes
PostPosted: Feb Wed 06, 2019 8:33 pm 
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Joined: Oct Sun 15, 2006 12:57 pm
Posts: 6189
Location: Liberty, Missouri
I agree with the "couple of sharp raps" on the table.

Decades ago the T-17 was very popular in private aviation, and they would slowly become unusable, so I simply told the customers to give'em a couple raps on the wood part of the counter here, and see if that fixes your problem, but if not, I have these shiny new electrovoice carbon mics for 39.95.

Fixed quite a few and sold quite a few, business was good, and happy customers to boot, regardless of the outcome. That eventually meant, even more repeat business.

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 Post subject: Re: SCR-274-N command set and T-17 microphone woes
PostPosted: Feb Wed 06, 2019 9:20 pm 
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Joined: Aug Mon 09, 2010 2:57 am
Posts: 463
Location: York PA.
Hi Dave

This is what I currently use:

https://www.mcveyelectronics.com/milita ... -prototype

This just showed on the AMForum:

http://amfone.net/Amforum/index.php?topic=44604.0

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 Post subject: Re: SCR-274-N command set and T-17 microphone woes
PostPosted: Feb Thu 07, 2019 8:27 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3573
Location: Monterey California USA
There seems to be two schools of thought on what happened to the T-17 after the war. The most common belief is that these mikes more or less failed after a few years as the carbon granules packed up and humidity got inside. It's probably safe to say that every single T-17 left by now has weak or almost no output. I have T-17's from estates that had already been modified with telephone parts back in the early 50's, using those big bullet-nosed E-series cartridges from 1930's desk phones of the 200 and 100 model ranges.

The other belief is that these were mostly used in aircraft which were very noisy and shouting into the mic was expected, and they were not supposed to have any more output than they do. I don't buy this because these were also used in ground equipment and if you had to shout when using it in that situation, you made yourself a target,

Also, the other microphones such as the RS-38 do not exhibit this problem and usually still work just fine.

For our purposes, whatever the reason, the T-17 will have to be modified with an electret or a more modern carbon cartridge, such as out of a 300 or 500 series desk phone handset. I don't know if anyone has figured out a way to reactivate the existing T-17 insert. I tried heat and got nowhere. Even rapping on it eventually quit giving results.
Some people have drilled a lot more holes in the cap, but I don't think this really helped and certainly makes the mike look ugly.

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 Post subject: Re: SCR-274-N command set and T-17 microphone woes
PostPosted: Feb Fri 08, 2019 2:58 am 
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Joined: Aug Mon 09, 2010 2:57 am
Posts: 463
Location: York PA.
Here's the output of the carbon element in my T-17:

Attachment:
t17bb.jpg
t17bb.jpg [ 64 KiB | Viewed 200 times ]


Here's the output with the McVey Electronics replacement:

Attachment:
t17cc.jpg
t17cc.jpg [ 69.02 KiB | Viewed 200 times ]


The McVey replacement in my T-17:

Attachment:
t17aa.jpg
t17aa.jpg [ 91.65 KiB | Viewed 200 times ]


And the finished T-17:

Attachment:
t17dd.jpg
t17dd.jpg [ 107.37 KiB | Viewed 200 times ]

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73 Mark K3MSB
www.k3msb.com


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