[ETO_Alpha] Re: Alpha 76

[Dave Haupt]

Robert,

The 76 feeds the cathodes through a broadband network
with no tuning elements.  If other amplifiers use a pi
network input, then the 76 might be lower gain (e.g.
"hard to drive").

Note also that there is a "low drive" modification to
the 76, documented on the AlphaRadioProducts web page.
 Make sure that you've performed that modification. 
The original 76 was designed to deliver 1kW INPUT
(roughly 650 watts output) from a 100W exciter
(typical exciters those days were 180 watts INPUT, and
delivered 100 to 120 watts output).  When the FCC
increased the amateur power limit to 1.5kW output,
many existing amp designs needed to do something to
increase the gain.

What Dahl xfmr did you use?  I have looked at the
possibility of running my 76 on higher anode voltage -
at stock anode voltage, the 3CX800A7s are being pushed
a bit for cathode current.  One solution would be to
add a third tube, but not sure there's room.  I was
hesitant to increase the anode voltage because that
might put the tune cap and bypass caps at risk.  I
gather that you haven't had any problems with them?

73,


Dave W8NF


>Date: Sat, 18 Jun 2005 00:30:17 -0500
>From: Robert Wood <rwood90 at direcway.com>
>Subject: [ETO_Alpha] Alpha 76>
>
>Have Alpha 76 converted to 3CX800's and the Dahl 
>higher >voltage 
>transformer.
>Others with experience on said conversion
>and feeding the inputs to these tubes.   Seem harder
to
>drive then other 3cx800 amps I've dealt with.

>73 w5aj

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