[Central-Electronics] 100V and SWR?

[George Maier]

Hi Eugene:

First of all, glad to hear another 100V is in service; great going.  Just
getting around to my email pile, so I hope this info is still needed.

The 100V/200V mismatch circuit is really a screen overload detector. 
When the PA screen current is beyond a specific limit, it draws enough
current to trip a relay that momentarily biases the grid to cut-off.  The
relay is in the PA compartment, and has one of those pesky low voltage, high
failure caps across it.  The cap should charge & discharge at a fairly fast
rate causing the relay to chatter.  If you ever heard it, you'd know it; it
sounds like the PA compartment is going fly apart. That is the "audible
alarm" the manual talks about. 

First thing, replace that cap across the relay ASAP. The relay coil must be
OK or you would not have screen voltage. Next, try your transmitter into a
known good load, then one with a VSWR of 2:1 to 3:1.  You should be able to
trigger the relay.  If all else fails, bring the power up slowly without any
load, but do not exceed the tube dissipation ratings (35W per tube).

If you've already done this, and it has not been successful, then we'll have
to dig a bit deeper.  Let us know what turns up.

73, George - W1LSB 




-----Original Message-----
From: central-electronics-bounces at mailman.qth.net
[mailto:central-electronics-bounces at mailman.qth.net] On Behalf Of Eugene
Hertz
Sent: Monday, November 06, 2006 11:50 AM
To: central-electronics at mailman.qth.net
Subject: [Central-Electronics] 100V and SWR?

Hello all,

I have read that the 100V has a measure of protection in the case of high
SWR.  Well, I put my first antenna up this past weekend and I had 3:1 on 80m
and infinity on 160m.  Yet, the mismatch indicator never indicated.  So to
test if this circuit was working, I disconnected the antenna altogether and
sllooowwwllly increased power from 0 to max (momentarily) so that I could
see this indicator work (and presumably to hear a relay actuate).  Yet I
heard and saw nothing.  Built-in o'scope showed a nice long vertical line as
I increased power but no mismatch.

Q's
1. Does anyone have experience as to how much SWR it should take to trigger
this thing?
2. Does anyone have a procedure I can use to make sure this protective
feature is operational?

Third unrelated question: The manual indicates that the hairline can be
adjusted so that the VFO display is right on target, I am guessing similarly
to how a collins R-388 or J4 works. Where is this adjustment? 
thanks
Eugene



_______________________________________________
Central-Electronics mailing list
Central-Electronics at mailman.qth.net
http://mailman.qth.net/mailman/listinfo/central-electronics