[Central-Electronics] 20A and relay output voltage

[Stan McIntosh]

Jim,



Thank you very much, and it’s great to hear from you.  I truly appreciate
your message.



>>The switching of 120vac for PTT is quite dangerous, and a fault in that
circuit can really

>>cause carnage.



Thanks, and I’m in full agreement.  I think that I mentioned working to
reverse the previous owner’s wiring to route 115 VAC through the relay
contacts.  When I first noticed it, my impulse was to ask the group if I’m
missing a solid reason for AC to the terminal screws.  After thinking a
bit, though, I decided that I simply didn’t want switched AC that way.
Besides, for my setup, all I want is a contact that is normally closed and
opens during transmit.



>>Staying with a switched 120 vac is easier.



If the AC was coming from a receptacle in the same manner as one of the
newer 20As, I’d leave it alone, but that’s not how mine was set up.  Mine
had two pigtail leads coming out in addition to having 110VAC switched
coming to screws 8 and 9 on the terminal strip.  That’s not the case,
anymore.  The



>>I would surely use a 3 wire power cord to make sure only the hot gets
switched instead of

>>the neutral.



Got a cord ready, but there’s a little more to do…hopefully tonight.  The
AC wiring in is a bit convoluted, and I want to deconvolute the path.  The
fuse looks to be in one leg with the switch in the other, which is a big
problem.  I need to get the return simplified with the fuse upstream of the
switch in the hot lead.



>>From a danger perspective, there are many issues with this equipment.



One safety feature missing from this, as well as many boat anchors, is a
lack of a bleeder system.  Would adding a couple of resistors really have
added that much to the BOM?  Even before making other changes, I usually go
in and add several bleeders in the B+ supply.  Years ago, someone
emphasized the value of using more than one bleeder with connections at
more than one B+ and more than one ground point, just in case one bleeder
path fails.



>>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.



Though some parts seem to handle the higher voltages, I’d really rather
stay within the component voltage ratings.  If we start making 6AG7’s in
the western hemisphere again, I might relax, even though they are rugged.
Reduced power output isn’t a concern.  If I need more punch, I have plenty
of parts for an afterburner, and then there’s the dual 813 amp that led to
me getting the 20A.



Here’s another question: can I prolong the green-eye’s life by cutting back
on the B+?  The 6E5 phosphor has a finite use-time, so would cutting back
on the B+ help?  The max rated voltage looks to be 250V, and the max
current is 4.5 mA.  So would something like 12k be a good place to start
for dropping 300V to 250V?



>>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.



That’s a very good idea, and it won’t be much work.  I’ve got some 10W 220Ω
resistors.





>>You might find this thread interesting:



>>http://amfone.net/Amforum/index.php?topic=37143.0


<http://amfone.net/Amforum/index.php?topic=37143.0>Hi.  I *might* find this
thread interesting?  This is one of the threads that got me excited when I
first got the 20A.  The whole thread is a great read, and I went through it
multiple times in December.  Thank you for reminding me because, now that
I’m getting back into the 20A, I need to read the messages again with
soldering iron in-hand.



I don’t remember if I posted just how I ended up with mine (, and I’m too
lazy to look back and see), but I hadn’t heard of Central Electronics or
the 20A when I went to see a friend in December.  He was wanting to clear
out a dual 813 amplifier that a Western Electric engineer built in the
1950s.  The amp is a work of art, and my friend was offering at a price I
couldn’t refuse.  Before I got there, he mentioned the 20A that he also
would be willing to throw in; it was a piece he hadn’t had time to get
into, and he didn’t think that he ever would.  I didn’t know anything about
the 20A, even when I was bringing it home.  And then I started to Google.
The thread that you pointed out is one of the first that I saw.  From
there, I just spent some time learning what I could about this piece.  If I
had to pick between the 20A and the amp that I drove to purchase, I’d keep
the 20A.



In December-January, I did get the 20A back running, though it needed 400V
to get the expected output.  However, then, as a friend used to say, ‘life
got in the way.’  Nothing happened at the bench again until May.



73

Stan