[Hallicrafters] SR-400 RF Output ???

[Sandy W5TVW]

I had an SR-400 for some time.  The neutralization was always rather squirrelley on that
rig.  You had to rather compromise.  IO think I used to do it on 15 meters and that turned
out to be not quite enough on 10 but "OK" and almost "right on 20.  40 and 80 always OK.

If you are getting 150 watts output that is enough!  The screen voltage is rather high
normally and the tubes have a tendency to "run away" if you are not careful.
Watch the value of the small cathode metering/current limiting resistors carefully.
If they are high or low in value you will set the idling current too high.
My radio used 6HF5 tubes in the PA.  Some versions use 6KD6's.  In ALL
cases, if your radio does not have a "muffin fan" installed on the rear
of the PA cage, by all means INSTALL ONE!  It will keep the tubes
cooler and they will last much longer.

I always tried to keep my RF output down to 100-125 watts max.  This will
also prolong the life of the tubes.  Expect less than that on 15 and 10 meters!
The tubes are not too efficient on those bands.

You can neutralize by removing plate and screen voltages, applying drive
only and monitoring RF output with a dummy load and RF voltmeter
across the dummy load.  Peak tune and load for maximum output and adjust
neutralizing cap for a null (on minimum output).  Repeat the "peak and null"
several times until no change is noted.  Check on 10/15 20 meters as you will
probably have to "fudge" the neutralizing cap adjustment to get the best
compromise onall bands.  80/40 meters will be OK and don't have to be checked.

Don't have a book handy so I'm working from memory!  Let me know if I can help
clear anything above up if you are confused.
73,
Sandy W5TVW
----- Original Message ----- 
From: <wd0x at adelphia.net>
To: <hallicrafters at mailman.qth.net>
Sent: Friday, May 05, 2006 7:09 PM
Subject: [Hallicrafters] SR-400 RF Output ???


| I'm hoping someone familiar with the proper operation of a SR-400 Cyclone transceiver (paired up
with a PS-500A-AC supply) can give me an idea of how much full rf output (not input) in watts in the
CW position is "normal" into a 50 ohm dummy load. I've been fiddling with one that has a new pair
of, idle plate current matched and neutralized, 6JH5 finals and a good driver tube.
|
| Best I can get on 80/40/20 meters is 150 watts CW output @ 350ma plate current. Output too low?
About right? PS-500A-AC has been completely rebuilt and all voltages (800vdc, 280vdc, -125vdc) &
idle plate current (70 ma) are correct. All caps and resistors in the PA circuit are OK. I'd really
appreciate some expert opinions/advice before I go any further.
|
| By the way... Anyone have a better method of neutralizing these finals besides the procedure
outlined in the manual? Somehow adjusting the neutralizing cap with full plate and screen voltage on
both finals seem like a great way to shorten the life of these nervous sweep tubes!  I have an Autek
RF-1 antenna analyzer that can transmit a weak signal to the PA stage. Seems like I did that once a
long time ago with a Johnson Valiant. Don't remember how I did it, hi........ Hmmmmmmmmmmmm
|
| Thanks, 73, Bill, wd0x
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