Didn't my response to you get published?
AM I BEING RESTRICTED FOR SOME REASON? I noticed a post taking all day
yesterday posted at 9:30 AM to make it up by evening. If this is the case
I'll take my knowledge elsewhere.
I answered your question over 24 hours ago.
The 746 has a computer monitored SWR foldback. This is the only ICOM to
have this aggressive setup except maybe the 7000.
AT 8 WATTS REFLECTED IT FOLDS BACK. This is not adjustable.
Your reflected power climbs as your forward power goes up and blammo
foldback.
YOU will need to TUNE your tuned input better.
BOB DD
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Mike
Sent: Tuesday, January 16, 2007 3:38 PM
To: amps@contesting.com
Subject: [Amps] Amp 10 m Output Fold Back Also on 15 m
Just found the same problem on 15 meters, except it occurs when the
power output reaches 1100 W. The output then drops to 400 W until
the drive or any other control that can influence the output (C1 or
C2 in the PIL tank circuit) causes the output to drop below 1100
W. 20, 40 and 80 work okay at full output (1500 W).
This power output drop occurs as a step function, e.g., at 1100 W
output the amp is normal, the instant the power is increased to more
than 1100 W the power drops to 400 W. No intermittent value, but 400
W. The same is true for 10 m other than the 800 W output power level
when the amp's output drops back to 400 W.
Also, when the power level is left at 400 W on 15/10 for more than a
second or two, a funny odor comes from the amp. The odor, as best I
can identify, smells like copper tarnish getting hot. Plenty of air
is being forced through the tube with spill-over into the tank
compartment. When the power out drops back to 400 W due to the
problem the grid and plate current decrease to approximately the
values seen at 400 W output under normal operation. If there is an
oscillation going on, wouldn't a plate/grid current increase be seen?
It seems the output is getting back into the input via the input
board? This is my present thought about the problem. If that is
what's happening, why is 400 W the resulting output level?
>Hello,
>
>Need help with figuring out why 10 meters doesn't work properly on a
>homemade GS35-B amp. when the pi network input circuit is used.
>
>Symptoms: without the 10 meters pi network input circuit connected,
>the amp. will put out ~1400 Watts on 28500 KHz with ~65 W from the
>IC746 (the IC746 internal ant. tuner used to match the amp.) The 10
>meters input pi network output capacitor, C2, a120 pF mica, is
>permanently mounted from the cathode to ground at the tube. When the
>rest of the10 meters input network is connected and the IC746's ant.
>tuner bypassed, only ~800 Watts output can be obtained before the
>output drops back to less than 400 Watts (fold back?) and the SWR on
>the IC746's SWR readout increases. When the output power is turned
>down to just below 800W, normal conditions return until power again
>is adjusted to the 800 W level.
>
>Conditions: The input networks C1 is a mica, variable, compression
>capacitor and has been adjusted for minimum SWR on the IC746. The
>network was designed using a Q of 2. A toroid is used for L1 in the
>input network. The amp works okay on other bands with the tuned
>input. A separate pi network relay selects the individual pi network
>for each band. The 10 meter input C2 is added to all the other
>bands' C2 value. 5000 pF mica capacitors are used to couple the
>input circuit to the cathode and across the tube's filament. The
>input board's output is less than an inch away from the
>cathode. Using a B&W FC15 as the filament choke. The amp input is
>being fed directly from the IC746 rather than go through the ant.
>transfer relay in an attempt to find the problem. Liberal
>application of 0.0015 uF disc capacitors has been made. All control
>lines have been bypassed with the 0.0015 pF capacitors at both ends.
>Chokes have been inserted in several of the lines going from the grid
>compartment to the control area.
>
>Need some more ideas to try to isolate the problem. What's causing
>the amp to not work properly with the input network?
>
> 73,
> Mike, K4GMH
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>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
73,
Mike, K4GMH
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