On Mon, 24 Oct 2005 00:56:14 -0700, MarkAren wrote:

Hi All,

I am contemplating the design of a class C amp for 144MHz using wound
output inductors and a split stator (butterfly) tuning cap. This seems to
be a very common approach in the good old days for QQV06-40As, but I don't
think that I have seen such a design for 250Bs in push pull.

There is a design for a 2M amp using a single 4CX250B in the old
RSGB VHF/UHF Manual. The inductor in the anode circuit is 3.5 turns
of 1/8 inch copper tube. The output coupling loop is 1 turn.

I don't see any reason why you couldn't make a push-pull
version with a pair of 250Bs.

The issue of voltage rating of the o/p cap is of course an issue, and the
output coupling loop will need to be well insulated (assume 1500VDC on the
anodes).

You can reduce the risk of frying the operator by grounding one
end of the output coupling loop.

Any obvious reason that this isn't a common approach ?

The only advantage I can see with this arrangment is a reduction
in the size of the amp. Since a 500W tube amp will require a large
power supply, I don't see much point in building a tiny PA.
A stripline amp will give greater efficiency and will only
be a little bit bigger.

73, C U on 2M. Ed. EI9GQ.

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