[ARC5] Addendum: IIRC Stinson’s solution to sidetone issue..

Sun Feb 10 22:38:56 EST 2019

The question addressed by Dave’s solution is “how does an operator zero beat a frequency using the SCR-274N system as originally configured?”

As originally configured, it can’t be done because in transmit mode. The receiver’s normal AF output is disconnected by the sidetone relay, and the sidetone signal is then routed to the rack’s headphone jacks.

Therefore Dave’s solution solves the problem and makes netting possible.
-Tom KE4RHH

Sent from my iPhone

Begin forwarded message:

From: Tom Bridgers <tarheel6 at msn.com<mailto:tarheel6 at msn.com>>
Date: February 10, 2019 at 10:15:57 PM EST
To: arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>
Subject: IIRC Stinson’s solution to sidetone issue

My memory is not as good as it use to be, but I thought I remember Dave’s solution was related to his interest in listening to the transmitted signal on his SCR-274N receiver that was in a rack and appropriately connected to a BC-456 modulator.

His innovative solution, was to add a spst switch to the rack that enables  the sidetone relay in the rack to be toggled off when transmitting.

With the sidetone relay toggled off, the receiver’s normal audio output remains connected to the rack’s headphone jacks.

And as I recall Dave telling me, even though the receivers antenna terminal is grounded (when in transmit mode), the receiver is nonetheless able to hear the transmitted signal and pass it through to the headphone jacks.

As we all know, Dave does not like to add a mod to any military radio system.  But this mod was born of necessity...

I hope I remembered it correctly and that my comments help further the sidetone options/issues discussion.

Apologies in advance to Dave for any errors on my part.
-Tom

Sent from my iPhone

On Feb 10, 2019, at 2:28 PM, arc5-request at mailman.qth.net<mailto:arc5-request at mailman.qth.net> wrote:

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Today's Topics:

 1. Re: SCR-274N side tone level? (Richard Knoppow)
 2. Re: SCR-274N side tone level? (Dave Kirk)
 3. Re: SCR-274N side tone level? (David Stinson)

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

Message: 1
Date: Sun, 10 Feb 2019 10:46:17 -0800
From: Richard Knoppow <1oldlens1 at ix.netcom.com<mailto:1oldlens1 at ix.netcom.com>>
To: arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>
Subject: Re: [ARC5] SCR-274N side tone level?
Message-ID: <b99f9f1b-8eb6-7662-dc5b-166636d1b235 at ix.netcom.com<mailto:b99f9f1b-8eb6-7662-dc5b-166636d1b235 at ix.netcom.com>>
Content-Type: text/plain; charset=utf-8; format=flowed

  No, I am talking about both sidetones and mentioned them in
my post. The come from different places but the load on either
transformer output is the same. If you put a pad of known
impedance on the headphone output of the rack it will work for
either side tone source. The winding on the modulator transformer
will be affected by the load on the headphone jacks but if its
loaded by a constant resistance pad of about the value that is
expected of the headphone line the modulator should work fine. A
pad will also isolate the headphone line so that changes in
headphone impedance will have little or no effect on the
transformer side. Many text books will show you how to make such
a pad. I suspect David's problem is that he used a low value pot
that partially shorted the headphone winding on the modulator
causing some overloading and distortion there. Even a simple L
pad with the series arm connected to the headphone output would
eliminate this. If the side tone, either CW or Phone, worked
originally it will still work.
   I read over the handobook for the SCR-274N before posting.
Its difficult in some areas because the schematic drawings are
broken up into sections but it is possible to trace through the
side tone circuits.
   The phones mentioned are 8K impedance, I have several. 8K is
the impedance, not the DC resistance as specified in many
headphones. Resistance is around 2K.

On 2/10/2019 1:25 AM, Robert Downs via ARC5 wrote:
Richard,

You are talking about the CW sidetone and Dave was talking about the voice sidetone.  Two different circuits in the BC-456.

Robert Downs

-----Original Message-----
From: arc5-bounces at mailman.qth.net<mailto:arc5-bounces at mailman.qth.net> [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Richard Knoppow
Sent: Sunday, February 10, 2019 01:06
To: arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>
Subject: Re: [ARC5] SCR-274N side tone level?

--
Richard Knoppow
1oldlens1 at ix.netcom.com<mailto:1oldlens1 at ix.netcom.com>
WB6KBL

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

Message: 2
Date: Sun, 10 Feb 2019 19:13:59 +0000 (UTC)
From: Dave Kirk <w6mqi at yahoo.com<mailto:w6mqi at yahoo.com>>
To: arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>, David Stinson <arc5 at ix.netcom.com<mailto:arc5 at ix.netcom.com>>
Subject: Re: [ARC5] SCR-274N side tone level?
Message-ID: <924898192.1272051.1549826039788 at mail.yahoo.com<mailto:924898192.1272051.1549826039788 at mail.yahoo.com>>
Content-Type: text/plain; charset="utf-8"

Okay guys I need to reset this whole conversation in my original post I mentioned that the CW side tone was too loud along with the phone side tone. My main concern is the CW side tone because I wear headphones while operating CW and the side tone is just ear piercing. So I did some test on the CW side tone, and was able to lower the volume with no problem, but now relay clicking in the headphones is prominent. Funny I didn't hear the relay clacking away in the headphones with the loud side tone:-), fix one problem another appears oh well. Anyway think I'll just let things be have to remember these are WW2 radios not some $10,000 2019 Icom and that's why I like them their quirky, and rough around the edges.
My next issue is to figure why the BC-455-B 40m receiver drifts so much it takes almost an hour for the receiver to settle down my other command set receivers are very stable.

Dave
   On Sunday, February 10, 2019, 5:06:38 AM PST, David Stinson <arc5 at ix.netcom.com<mailto:arc5 at ix.netcom.com>> wrote:

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Caution:
If you try putting a pot across the sidetone winding, rather than in series with it,

the impedance change this makes is reflected into the other windings of the

modulation transformer and will change your modulation envelope.? It changed

mine drastically when I tried this.?? In fact, any non-spec load on the sidetone

winding causes tx modulation envelope effects. It?s been a lot of years now

and I don?t remember the exact details, but ended-up abandoning the sidetone

line altogether in my sets.
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Message: 3
Date: Sun, 10 Feb 2019 13:28:00 -0600
From: "David Stinson" <arc5 at ix.netcom.com<mailto:arc5 at ix.netcom.com>>
To: "ARC-5" <arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>>
Subject: Re: [ARC5] SCR-274N side tone level?
Message-ID: <[email protected]<mailto:[email protected]>>
Content-Type: text/plain; charset="utf-8"

Try what worked well on the TCS set.
Connect two 5V Zener diodes across the headphone jack, one

pointed in each direction.  Made the headphones on the TCS

as comfortable as any other ham rig.   Lots of talk about how

?it won?t work,? but it works just fine.  I don?t explain it;

I just report it.  Pic:
https://photos.app.goo.gl/X6v2VtKWcp75AqQT6

GL OM DE Dave AB5S

From: Dave Kirk [mailto:w6mqi at yahoo.com]
Subject: Re: [ARC5] SCR-274N side tone level?

Okay guys I need to reset this whole conversation in my original post I mentioned that the CW side tone was too loud along with the phone side tone. My main concern is the CW side tone because I wear headphones while operating CW and the side tone is just ear piercing. So I did some test on the CW side tone, and was able to lower the volume with no problem, but now relay clicking in the headphones is prominent. Funny I didn't hear the relay clacking away in the headphones with the loud side tone:-), fix one problem another appears oh well. Anyway think I'll just let things be have to remember these are WW2 radios not some $10,000 2019 Icom and that's why I like them their quirky, and rough around the edges.

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