A pi network on 2 meters? Never work.
I've had a couple of tetrode amps for 2, one was the old classic plumbers
delight push pull amp with a pair of 4CX250s. That worked OK. A much better
design is a 1/4 wavelength stripline using either 4CX250s or 8930s. That amp
was sold by ARCOS a few years ago.
The stripline design is better with better efficiency. A problem however is
IMD with those tetrodes. It's a bit high and those tubes require a fairly
complex power supply with a screen supply that must not only be capable of
sourcing voltage, but also sinking it. Negative screen current is normal
with those tetrode amps. I'd bet the 4CX800s would work well in that
configuration too.
Triodes are much better. The W6PO amp using the 8877 is an excellent design.
A similar design could be constructed with the Russian tubes or the Eimac
triodes like the 3CX800 or 3CX1200. The IMD with these amps is much better.
If you're only operating CW or FM there's not much difference. On SSB the
triode designs with lower IMD are a far better choice. Your neighbors (hams
nearby) will appreciate it. On VHF/UHF nearby stations are REALLY loud. The
tetrode amps will make you VERY wide at your neighbors houses even if you
run them properly. The high order IMD products (7th, 9th, 11th, 13th) are
still quite strong when you're 100+ dB above their noise floor.
73 es GL,
Jerry, K0TV
----- Original Message -----
From: "David King" <G6KWA@thersgb.net>
To: <amps@contesting.com>
Sent: Thursday, September 09, 2004 4:50 PM
Subject: [Amps] 2m Linear Amp Enquiry
>
>
>
> Has anybody got experience of the Amp listed in the Tech web pages of
> 6m.com? It was for 2m using 2-4cx250b (shown as Horizons 12-62) zip file
c5
> It looks easy to build, and has a PI output network. I guess it was an
> early design but with some
> modifications (say better grid bias and screen protection, etc.), would it
/
> did it
> give good performance compared to other designs?
>
> David
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
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