[ARC5] SCR-274N side tone level?

Sat Feb 9 18:26:50 EST 2019

 Did a quick test with a pot on the side tone line tried 10k not much difference, 50k was much better still not enough, so looks like maybe a 100k pot might do the trick. Also switched the Hi-z connection on T-50 to Low-z didn't make any difference to my ears. Made my first AM contact today with the SCR-274N setup Q5 with a clean audio report as clean as a carbon mic can be anyway never have liked the sound of carbon mic's.

Dave

    On Saturday, February 9, 2019, 1:48:57 PM PST, Michael Hanz <aaf-radio-1 at aafradio.org> wrote:  

  Of course, don't forget that to authentically calculate that output voltage, one must take the square root of 6.667 by using Prime Factorization method.  No fair using a computer.  

 Running and dodging,
  - Mike

 On 2/9/2019 2:31 PM, Robert Downs via ARC5 wrote:

#yiv6510858935 #yiv6510858935 -- _filtered #yiv6510858935 {panose-1:2 4 5 3 5 4 6 3 2 4;} _filtered #yiv6510858935 {font-family:Calibri;panose-1:2 15 5 2 2 2 4 3 2 4;} _filtered #yiv6510858935 {font-family:Tahoma;panose-1:2 11 6 4 3 5 4 4 2 4;}#yiv6510858935 #yiv6510858935 p.yiv6510858935MsoNormal, #yiv6510858935 li.yiv6510858935MsoNormal, #yiv6510858935 div.yiv6510858935MsoNormal {margin:0in;margin-bottom:.0001pt;font-size:12.0pt;font-family:New;color:black;}#yiv6510858935 a:link, #yiv6510858935 span.yiv6510858935MsoHyperlink {color:blue;text-decoration:underline;}#yiv6510858935 a:visited, #yiv6510858935 span.yiv6510858935MsoHyperlinkFollowed {color:purple;text-decoration:underline;}#yiv6510858935 span.yiv6510858935moz-smiley-s1 {}#yiv6510858935 span.yiv6510858935EmailStyle18 {color:#1F497D;}#yiv6510858935 .yiv6510858935MsoChpDefault {font-size:10.0pt;} _filtered #yiv6510858935 {margin:1.0in 1.0in 1.0in 1.0in;}#yiv6510858935 div.yiv6510858935WordSection1 {}#yiv6510858935  
I had forgotten about that.  If your BC-456 is a BC-456-B or BC-456-E and is strapped for HI-Z audio, changing the two transformer connections to LO-Z will reduce the voice and CW  sidetone output voltage by theoretically SQRT(6.667) without having any effect one way or the other on the receiver audio, regardless of what mix of receivers you have.

Robert Downs

From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On Behalf Of Michael Hanz
 Sent: Saturday, February 9, 2019 10:49
 To: Dave Kirk; arc5 at mailman.qth.net
 Subject: Re: [ARC5] SCR-274N side tone level?

Table 8 in the manual says the sidetone voltage on CW is 7-9 volts into 4,000 ohms.  Are you using low impedance earphones?  If you are, you might try an MC-385* headset adapter to lower the volume.   Or, you might check to see if you have a low impedance tap on the sidetone transformer, T-50, in your modulator.  Here's the note on the tap:

 Or, you could just put an appropriate resistor in series with the jack to your headphones...:-)

  - Mike  KC4TOS

On 2/9/2019 10:52 AM, Dave Kirk via ARC5 wrote:

I run a stock SCR-274N setup with a BC-456 modulator not sure if this is normal, but the side tone in CW, and phone is ear piercing I can't even wear my headphones its so loud. Is there a simple way to lower the level? So far I haven't seen in the manual any mention of level adjustment. Guess I understand why its loud the radio dude needed to be able to hear the radio during flight, but dang this is ridiculous.

Dave 

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