[ARC5] SCR-274N side tone level?

[Dave Kirk]

 Hi guys, Yes I had the pot in series will try as a shunt tomorrow. 
Robert your right I forgot to move T-52 tap as well helps to read the note all the way through. 
Brian I have 2 MC-385's so no need for anymore thanks for the offer. 

I'll report back tomorrow hopefully with more positive results.
Dave

    On Saturday, February 9, 2019, 5:24:46 PM PST, Richard Knoppow <1oldlens1 at ix.netcom.com> wrote:  
 
   If you use a pot the pot should be across the output and the 
wiper to one side to the phones. That should regulate the level.
  For the most part a 500 ohm output will feed almost any 
headphone set of medium (500 ohms) to high impedance (10 to 25K). 
The low impedance phones will be louder. Many tube short wave 
receivers have a headphone jack across the speaker line, usually 
around  4 to 8 ohms. This will work with high impedance phones 
just fine. Several volts across almost any headphones will be 
deafeningly loud. Put a pot across the output and see what that 
does.
    Carbon mics vary but all have noise and many have rather a 
lot of distortion. The best of them was the capsule used in the 
Type 500 telephone. The noise increases as moisture gets into the 
carbon particles. Sometimes baking the mic will help but often it 
won't. If the mic has been subjected to too much current the 
points of the carbon particles will have been burned making the 
mic more noisy and lowering its level. Carbon mics should be run 
with the minimum current that will produce a useful output.
    Carbon mics are amplifiers. The output level can have more 
energy than the sound wave producing it. That is one reason they 
were so popular for telephone and communications use. They are 
also relatively rugged. They have been almost completely 
supplanted by electret mics which must have a built in impedance 
matching device which can also be an amplifier. So they can have 
output as high as a carbon mic with far better audio quality and 
similar ruggedness. They are also cheap to make.
On 2/9/2019 3:26 PM, Dave Kirk via ARC5 wrote:
> 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

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