[Amps] Power from Pair of Eimac 4 x 150 a / 7034?

[Carl]

> Date: Sun, 28 Dec 2014 11:00:32 -0500
> From: "Carl" <km1h at jeremy.qozzy.com>
> To: "Jim Thomson" <jim.thom at telus.net>, <amps at 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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