[ARC5] ARC5 Digest, Vol 159, Issue 30

Mon Apr 17 08:30:28 EDT 2017

Oops. I apologize. That last posting was a summary note that I meant to send just to myself for my files.
Tom KE4RHH

Sent from my Sprint Tablet.

On Apr 17, 2017 8:24 AM, arc5-request at mailman.qth.net wrote:
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Today's Topics:

   1. Removing unwanted sidetone feedback in speaker in AM
      (Tom Bridgers)

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Message: 1
Date: Mon, 17 Apr 2017 12:24:19 +0000
From: Tom Bridgers <tarheel6 at msn.com>
To: ARC 5 list ARC5 <arc5 at mailman.qth.net>
Subject: [ARC5] Removing unwanted sidetone feedback in speaker in AM
Message-ID:
        <DM5PR19MB1548F5C34C862E5DB86B955A90060 at DM5PR19MB1548.namprd19.prod.outlook.com>

Content-Type: text/plain; charset="utf-8"

Stinson says unwanted sidetone feedback in AM when using a speaker is normal but can be resolved.  Why normal? System was designed to be used with headphones which wouldn't cause the feedback problem in normal military service.

Resolution?
Disconnect the wiring that enables the sidetone function.
-Or-
Add resistance to reduce the sidetone volume.
-T

Sent from my Sprint Tablet.the

On Apr 17, 2017 3:09 AM, arc5-request at mailman.qth.net wrote:
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Today's Topics:

   1. Re: [Milsurplus] ID Ham-Modified Command Set TX? (Mike Everette)
   2. First AM QSO with the SCR-274! (J Mcvey)
   3. Re: First AM QSO with the SCR-274! (David Stinson)
   4. Re: First AM QSO with the SCR-274! (Brian)

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Message: 1
Date: Mon, 17 Apr 2017 01:13:48 +0000 (UTC)
From: Mike Everette <radiocompass at yahoo.com>
To: Mike Morrow <kk5f at arrl.net>, Don Merz <n3rht at yahoo.com>,     ARC-5
        List <arc5 at mailman.qth.net>, milsurplus <milsurplus at mailman.qth.net>
Subject: Re: [ARC5] [Milsurplus] ID Ham-Modified Command Set TX?
Message-ID: <819844938.224976.1492391628111 at mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"

This conversion was published the the CQ Command Sets Handbook. ?You're right, it's a conversion to an external VFO.
73
MikeWA4DLF

      From: Mike Morrow <kk5f at earthlink.net>
 To: Don Merz <n3rht at yahoo.com>; ARC-5 List <arc5 at mailman.qth.net>; milsurplus <milsurplus at mailman.qth.net>
 Sent: Sunday, April 16, 2017 4:40 PM
 Subject: Re: [ARC5] [Milsurplus] ID Ham-Modified Command Set TX?

It sounds like one of the very common mods to make an external VFO for some ham transmitter ( home-made and commercial.
Mike / KK5F

-----Original Message-----
From: Don Merz via Milsurplus
Sent: Apr 16, 2017 12:41 PM
To: ARC-5 List , milsurplus
Subject: [Milsurplus] ID Ham-Modified Command Set TX?

Estate sale I went to delivered a homebrew, ham-modified 80M transmitter made out of an 80M command set transmitter. The odd part is that the whole thing is collapsed into a unit no deeper than 4-5 inches. So all the 1625 tube area, the roller inductor, etc. is all gone. What's left is the front panel with dial, and 3 tubes in the rear--two 6AG7s and a VR-150 regulator, One the back is an SO-239 and octal p[ower connector. The front has only the dial, a 1/4 inch jack for the key I assume and a toggle switch.
Can anyone pint me to the source of this modified rig/VFO?
73, Don Merz, N3RHT

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Message: 2
Date: Mon, 17 Apr 2017 01:46:45 +0000 (UTC)
From: J Mcvey <ac2eu at yahoo.com>
To: "ARC5 at mailman.qth.net" <ARC5 at mailman.qth.net>
Subject: [ARC5] First AM QSO with the SCR-274!
Message-ID: <850645817.1427086.1492393605827 at mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"

OK , the guy was only 40 miles away, but I'll take what I can get!He was familiar with the ARC radios and said it had the classic military audio.The mike I used has a carbon cartridge with the simple 'mike booster" circuit consisting of a transistor and 2.2k resistor.Haven't built my electret circuit into a mike yet, but I will get to it soon. The prototype worked well when I did a live test on the modulator. It has more amplitude/gain? than what I used today.
It worked pretty well well with a 4:1 unun with a series cap to match the 80 meter dipole. Had to experimet with cap but I need about 150 pf on 80 meters? ( it's on a junk box variable cap from a military tuning box, with the plates meshed, so I'll remeasure it to be sure) . Tried 100pf and 40 pf fixed caps, but couldn't get it to load with those.
The power meter says it's a little over 50 watts on CW and maybe 12 watts carrier on AM.
The inductor is happy at? around 1/3 around 3885.
Interestingly, the current meter reads just under 2 amps on CW but the power meter says >50.?

I have not hooked up the sidetone/receive mute to the receiver rack and the feedback was very bad even with the sensitivity control all the way down.It was usable that way with CW, but not so much with AM!
I'm wondering if the the grounding contact on the T/R relay might need some cleaning or is there really that much leakage into the receivers?
After rewiring everything? into it's "portable radio desk", I'm glad it worked on the first try....

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Message: 3
Date: Sun, 16 Apr 2017 21:29:36 -0500
From: "David Stinson" <arc5 at ix.netcom.com>
To: "J Mcvey" <ac2eu at yahoo.com>,        <ARC5 at mailman.qth.net>
Subject: Re: [ARC5] First AM QSO with the SCR-274!
Message-ID: <8EE957A18C0B4D2684AA262D0D8D128F at DaddyPC>
Content-Type: text/plain; format=flowed; charset="UTF-8";
        reply-type=original

Congrats, good sir!
It's not receiver feedback.  It's normal "sidetone"
which is at the same level no matter where you
put the receiver volume control (can anyone say why?).
Normally, the sidetone goes to the headphones via
an intercom so it's isolated from the microphone.
When you use a speaker, feedback is the result.
I either introduce a lot of resistance to tone it down
or just disconnect the sidetone altogether.

----- Original Message -----
From: "J Mcvey via ARC5" <arc5 at mailman.qth.net>

I have not hooked up the sidetone/receive mute to the receiver
rack and the feedback was very bad even with the sensitivity
control all the way down.It was usable that way with CW, but not
so much with AM!
I'm wondering if the the grounding contact on the T/R relay might
need some cleaning or is there really that much leakage into the
receivers?

------------------------------

Message: 4
Date: Mon, 17 Apr 2017 17:09:21 +1000
From: "Brian" <brianclarke01 at optusnet.com.au>
To: "J Mcvey" <ac2eu at yahoo.com>,        <ARC5 at mailman.qth.net>
Subject: Re: [ARC5] First AM QSO with the SCR-274!
Message-ID: <D6BBE1662D20462D95430F39A2043BA7 at BrianPC>
Content-Type: text/plain; charset="utf-8"

Good work!
How did you measure 2 A? That is, what current meter?
What did the output look like on a CRO? If there was distortion on your output, then power output includes all the distortion components as well as the intended carrier.

73 de Brian, VK2GCE

On Monday, April 17, 2017 11:46 AM, you said:

<snip>
The power meter says it's a little over 50 watts on CW and maybe 12 watts carrier on AM.

The inductor is happy at  around 1/3 around 3885.

Interestingly, the current meter reads just under 2 amps on CW but the power meter says >50.
<snip>

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End of ARC5 Digest, Vol 159, Issue 30
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