[ARC5] Bypass Cap Question

[Roy Morgan]

On Nov 25, 2013, at 1:32 PM, Mark K3MSB <mark.k3msb at gmail.com> wrote:

> Guys –
> 
> Thanks for the info;  much appreciated!
> 
> On the transmitter, do the bypass caps need to be at the rear connector, or
> can they be at the tube sockets?  I supposed the rear connector is optimal,
> but from past experience working in that small area isn’t pleasant for me
> (vision issues).

Mark,

AT LEAST SOME of them need to go at the rear power socket:  for instance the B+ leads may go to the tubes via dropping resistor or such.  I don’t remember the schematic well but there may well be bypass caps at the tube socket (or nearby) for screen and cathode.  The plate B+ certainly goes via an RF choke (“shunt feed”) or the RF plate tank coil ("series feed”) and almost certainly there is a bypass cap at that point.  It *could* be that these bypass caps or one of them is open, thus causing wandering RF.

In addition, a wire from the socket to the rear connector could possibly pick up enough RF to cause trouble.  It could act as a short antenna inside the radio with an RF ground at the socket.  Bypassing at the rear power connector reduces this chance considerably.

If you have trouble putting caps at the rear connector, you might do about as well to put them inside the mating connector - in the rack if you use one, or in a cable shell if that is what you have, or even at the outside rear of the chassis if your supply wires are soldered onto the rear connector as in the transmitters I have here (ugh!).

By the way, if your transmitters have soldered-up rear original connectors, it may be possible to clean the solder out of them and return to original rack mount connectors.  It’s a good job to accomplish if both: you can manage it, and you have the rack(s) to use.

Roy

Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958 - Keep 'em Glowing!