[Central-Electronics] 20A and relay output voltage

[Jim Candela]

Stan,
The switching of 120vac for PTT is quite dangerous, and a fault in that circuit can really cause carnage. Any changes made need to followed by changes to whatever the 20A is switching, such as the amplifier keying, or a T/R relay. Staying with a switched 120 vac is easier. I would surely use a 3 wire power cord to make sure only the hot gets switched instead of the neutral. 

>From a danger perspective, there are many issues with this equipment. Think about the B+ dropping resistor behind the BC-458 modified VFO! Ouch!!
Your conversion from cap input to choke input will definitely drop the level of heat in that box, and as you noticed, will drop the RF power. One thing about that is the AC ripple rejection will be less, and this ripple will limit the depth of the carrier null. One suggestion might be to add an additional R-C in the B+ path which feeds the lower level RF and AF stages. Maybe something like 220 ohms WW and 40 uf. The lower B+ to the 9 Mhz oscillator will decrease the RF drive though...Keep full B+ to the 6AG7's.
You might find this thread interesting:
http://amfone.net/Amforum/index.php?topic=37143.0
JimWd5JKO



      From: Stan McIntosh <mcinsand at gmail.com>
 To: central-electronics at mailman.qth.net 
 Sent: Monday, July 3, 2017 6:59 AM
 Subject: [Central-Electronics] 20A and relay output voltage
   
Hello all,

I joined late last year after a 20A fell into my lap, and then some things
interfered with radio play for a few months.  After digging out, I'm now
digging back in.

After recapping, mine had a B+ of around 400V.  Moving the capacitor in the
power supply to make it purely choke-fed dropped B+ to just over 300V,
which then dropped the output to 1-2 Watts.

Last week, I put the 20A back on the bench.  The 10k resistor in the
negative voltage divider had drifted to 15k over the years.  Replacing it
got the output to 10 Watts with a 40 meter rock plugged into the front
panel.

Mine (SN 4434) is apparently too early to have the antenna relay plug in
the back, but a previous owner did wire the 115 through the relay and
terminal positions 8-10 on the back panel.  I started reversing that last
night to take the relay outputs back to the original configurations.  Even
if/when I do find a rack to house my 20A, I'd rather not have exposed hot
contacts.  Also, that'll make the 20A easier to connect with the R4B muting
connection.

This one's getting close to being ready to take out on the air.

73
Stan
KD4BTH
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