Hi Guys,
Just had my first QSO with the '78. There was a special event station
calling CQ. I answered him barefoot, he didn't get my call. Then I
pressed the "SSB" button on the Alpha and called him again. No
problem. "What did you do?" he asked. He said I want from 5/6 to 20
over S9. Sounds a little extreme actually, but that's what the man
said.
Nice amp. Very solid. Using the bandpass feature, no peaking and
tweeking whatsoever. Fan's a little loud. Also, I can feel it through
the operating table. I see Alpha sells a new fan for $65, I might
indulge. I could try taking the existing one out and renewing
the foam packing or somesuch but it's a bit of a bear to get at it, and I
think I might as well have a new part in hand when I take it apart. I
wonder how hard it would be to vary the fan speed? I'm thinking two
speeds - one for transmitting and cooling down after transmitting, and the
second
speed for receive/idle. A resistor across a relay....
This amp really wants 220VAC. It does work, but only gives about 900W.
I think it's because the HV regulation is not good running off 110. The
2200V sags down to about 1600 under load. Last night I thought of trying
my "cheap & dirty 220" trick. You find two 110 sockets that are on
opposite phases, build a box that plugs into each, and has a 220V socket.
I actually built such a box for welding in the field. It has a 220V 15A
breaker in it. That guarantees that in case of an overload, both phases
will be turned off - the 15A breaker in the box trips before the 20A
breaker in the building. Alas, all the 110V on this floor of the house is
on the same phase. So it looks like the procedure will be to go to the
County and pull a permit and install proper 220. I don't see that
happening
before the end of the year, I have so many projects lined up.
Those three little unobtanium tubes are worrisome. Some people have
replaced them with 2 3CX800A7 tubes. Which actually raises the plate
dissipation from 1200W to 1600W. The input and output stuff all works,
and
the amp tunes the same. Even uses the same tube sockets. Might have to
repeak the bandpass networks. The only complication is that the 3CX800A7
has a different filament voltage. And the box is really REALLY full. I
don't see where another transformer can be shoehorned in. Yet people do
it. Alpha's blog suggested mounting it in the RF section. I guess a
transformer doesn't care about being immersed in an RF field - as long as
nothing arcs. Would have to take care to bypass it good so I don't feed
RF back to the AC circuitry.
Even though the amp works fine now, I will be accumulating parts to do
this mod. I predict that some years from now, if and when these little
tubes actually die, the 3CX800A7 will be the same unobtanium as the
8874's are now. So better get'em while the getting is good. As soon as
the toy fund recovers from this purchase. Right now, it stands at
$0.00.
I was planning to get by on 110V by using the CW position. Have
changed my feeling on that completely. The CW position is harder to
drive, and you tend to run more grid current. So SSB position it is.
- Jerry Kaidor, KF6VB
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