Date: Sun, 28 Dec 2014 11:00:32 -0500
From: "Carl" <km1h@jeremy.qozzy.com>
To: "Jim Thomson" <jim.thom@telus.net>, <amps@contesting.com>
Subject: Re: [Amps] Power from Pair of Eimac 4 x 150 a / 7034?
He is asking about a PAIR of tubes in an amp he is looking at.
One option there is that other tubes in the 4X150/250 family can be used
that offer much better IMD
For many a $700 Chinese 8877 is not an option.
Carl
KM1H
## I stand corrected. A local buddy built a single 4-250A for 6m.
Another local friend built a single 3-500Z for 6m...and wiped out
every 49 mhz cordless phone for .25 mile radius. Both those amps
did just fine on 6m.
## My understanding was the 4CX-250B has sub par imd ? If that’s
the case, why use it. I don’t operate 6m..so have no clue how crowded it
gets
on ssb.
Jim VE7RF
The 4CX250B is a pretty horrible SSB tube when run at its high side of
"Typical Specs" even with rather obsolete ways of regulating screen and grid
voltages. Using. G3SEK's method picks up about a 5dB IMD improvement.
They are still popular since they are so cheap from NOS surplus but using
pulls that have screen emission really sound bad.
6M is full of CBers and others that never learned how to tune or adjust
anything plus so many of the all band multi modes are pretty horrible to
start with. Add garbage rigs to garbage amps, including most SS, and you
decrease the resultant IMD quality even further.
Since 6M is often a very atmospherically quiet band and signals can be VERY
strong, the combination of IMD and phase noise takes out big chunks and
buries the weak signals. Over 90% of my 6M DXing is on CW for that reason
and a lot of DX uses CW.
Carl
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