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Sweep Tub amps and freq. response

Nov 4th 2019, 11:43

gordyburdo

Joined: Nov 29th 2013, 18:14
Total Topics: 0
Total Posts: 0
Hello all, I have 2 sweep tube amps, a Swan 1200X and a converted Palomar 350Z. Both use 6lb6s in grounded grid. They are both working fine, but I noticed that the output on 75, 40, and 20 is over 400 watts with 100 watts drive. This drops to 380 on 15 and 350 on 10. Is this normal or do I have a problem with the rig? Thanks for any responses and 73, Gordy - WA2RUP
Nov 4th 2019, 16:54

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
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Total Posts: 0
A lot of amps don't do as well on 10M.
Nov 5th 2019, 14:06

WB1GCM

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Sounds like normal power output on the higher bands.

100 Watts drive sounds a little high for such an amplifier. If you can, plot the input power versus the output power, on a graph. Start with 10 watts drive and make a power output measurement at 10 Watt increments (of drive). The relationship between the two should be linear (a straight line on the graph). Near the top of the graph, it should curve (amplifier reaches saturation). Use an input power along the straight line of the graph to operate your amplifier in a linear fashion. Operating at, or past the saturation point will increase (transmit) intermodulation distortion, resulting in an abnormally wide signal.

Bob Allison
WB1GCM
ARRL Lab
Nov 5th 2019, 19:49

wa2rup

Joined: Nov 30th 2017, 09:54
Total Topics: 0
Total Posts: 0
Thanks to both who replied. I did make sure I wasn't over-driving the amp. Recommended drive is 100-125, but whatever power level I used, the gain factor was much lower on 10 meters. I didn't think tubes rolled off the way solid state devices do, but I must be wrong.

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