A much simpler solution would be to use a 50Ohm resistor, no un-un, and more
drive power. I don't know what the tube(s) is you are trying to drive, but
for example a pair of GU74B's would require about 50W drive in to 50Ohms and
give 2KW PEP out.
- Paul KW7Y
-----Original Message-----
From: Amps <amps-bounces@contesting.com> On Behalf Of jim.thom
jim.thom@telus.net
Sent: Saturday, October 23, 2021 9:43 AM
To: amps@contesting.com
Subject: [Amps] 1:9 un-un for grid driven tetrode
A buddy is trying to get a 1:9 un-un to work on his grid driven tetrode.
Terminated in a 450 ohm globar, SWR is 1:1 but only up to aprx 20 mhz.
Above 20 mhz, it rapidly all goes to hell....reaching 2.5:1 at 29.00
mhz. ( this on the test bench)
He needs the 1:9 un-un to work from 80-10m. What's the trick here ?
What is the ideal material to wind the trifilar onto ?
Once eventually installed into the amp, a small coil is wired in parallel
with the 450 ohm globar to cancel out the XC from the tube, but that is a
normal procedure, and will not alleviate the high swr issue on the upper
bands.
Jim VE7RF
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