On Feb 23, 2005, at 5:22 PM, K3vw@aol.com wrote:
> I say the AL-1500 for several reasons. The 1500 has a grid trip
> protection
> circuit, the 1200 does not.
No grid-trip protection circuit that I've seen yet is capable of
tripping during an 8877's 50a or so burst of grid current during an
unloaded oscillation condition.
> The 1200 has a neutralizing circuit to keep it from
> oscilatting on 10 meters,
The "neutralizing circuit" is the one that Heath Warrior and Gonset
GSB-201 used in their 811A amplifiers. The reason this neutralization
circuit was abandoned is that, even though it worked semi-ok at 10m, it
contributed to VHF parasitic oscillation due to the unavoidable phase
shift as freq increased. The bottom-line is that when phase-shift is
right, an amplifier can take flight.
> the 1500 is stable.
Not according to some of the owners that I've spoken with. The AL-1500
is apparently the only HF amplifier that has ever been manufactured
that has no parasitic suppressor. Are all the manufactures that use a
suppressor wrong? Is everybody marching out of step except Johnny?
Ref: Figure 24 on my Web site.
> The 1200 uses about 160 watts of
> filament wattage, the 1500 uses 50 watts. The 1200 needs about 100 to
> 150
> watts drive for full output,
Eimac says the 3cx1200A7 needs about 80w of drive.
> the 1500 needs about 85 watts drive. The replacement
> cost is about the same now and used 8877's are easier to find than
> 1200's. If
> I had another AL-1200, I would put a 3CX 1200Z7 tube in it and
> aleviate some
> of the problems. Willy K3VW
Good idea, however, the Z7 requires a different socket and a different
fil V, plus one has to do business with Eddie RichardS$$on.
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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