[Amps] Amps Digest, Vol 26, Issue 85

[R.Measures]

On Feb 23, 2005, at 5:22 PM, K3vw at 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