[ARC5] SCR-274N side tone level?

[Richard Knoppow]

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


-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL