[ARC5] ARC5 CW Question

[David Stinson]

----- Original Message ----- 
From: "J Mcvey via ARC5" <arc5 at mailman.qth.net>
Subject: Re: [ARC5] ARC5 CW Question


>I believe those receiver relays only served to put 
>the side tone from the MD7 into the headphones.

The relays mute the audio output of the receivers 
during transmit.  It's all the muting there is 
and all they need.

> I assumed the tx tone should be audible if the BFO
> is on in receiver.?
When the set is in CW or MCW mode, 
an actual tone generated in the MD7 
is fed to the sidetone line.

Which can be VERY load in headphones and
keying relay clicks will drive you deaf.  
I don't use the sidetone line.  You must be 
very careful trying to "pad" it;  anything you do on 
the Sidetone winding of the mod transformer is going
to be reflected to the other windings and affect 
modulation.  A high series resistance can be made
to work.  I tried limiting diodes ala telephone 
receiver elements and the reflections when they 
clipped also clipped the plate modulation.

>I am still wondering about contact failure of K52 
>snce they are keying ALL of the Tx B+ through
> K52 in the MD7 any guesses as to why
> they did it this way? 

Because the design works very well and 
the relay can handle it.
Keying the Osc. means you're going to need to supply 
fixed bias to the PA or clamp the screen during key-up 
like they do in a Johnson Ranger.  
Keying both the OSC and PA introduces 
timing issues that can lead to severe chirp.  
Keyed B+ finds the stages all loaded properly 
and ready to work.  If there is serious chirp
when keyed this way, there is some other problem.