[AMPS] Alpha 78

[David B. Ritchie]

Its a great amp; the tubes are 8874s (the aircooled version of the 
8873/4/5 series); the resistor array mounted below the tube deck is a 
padding arrangement to allow 100+ watt transceivers like Collins, Drake 
to operate with the amp easily -- normally shouldn't take more than about 
50 - 60 watts to max it out.  With brand new tubes, you can get > 2000 
watts out on 20 M -- more typically you should get around 1500.  To get 
1500 you need to get it tuned up very carefully --
1) if you use bandpass tuning, you might want to tweak the bandpass caps 
to mate with your antennas;
2) if you use manual tuning, a two tone test and an oscilloscope are very 
good for getting it properly tuned (e.g., TS950 series and SM230);
if your antennas aren't exactly 50 ohms and you use bandpass, you'll get 
a little less power out, but it really shouldn't make much difference.

Make sure you get/have an instruction manual -- they are still available 
from Alpha-Power (970-535-4173)

If your front panel is grundgy (they used an epoxy-velour paint 
originally which decomposes in ozone) I have a spare for sale for $80 on 
an exchange basis.

Good luck
Dave N7UE


On Sun, 4 May 1997, Ernesto M. Grueneberg wrote:

> Hi guys:
> 
> 	While watching the alpha 78's manual, I realized it has some resistors in parallel between the rf from the exciter and the 8875s Can't remember how many, but the value was 15 ohms. I wonder what purpose they serve, with such a low value and also wonder if they can be removed, to increase drive => output power??
> 	besides, anyone can provide any hints about this fine amplifier. I'm only able to get 1,1 KW (with 100 W drive) and thought it should be at least 1.5 KW.
> 
> 	Thanks for any answer.
> 
> Ernesto LU6BEG  
> 
> 
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David B. Ritchie, Esq.
D'Alessandro & Ritchie, P.C. -- Intellectual Property Lawyers
3521 E. Yorkshire Road, Pasadena, CA  91107-5432
818-683-8800 (TEL)   818-683-8900 (FAX)   dbr@alumni.caltech.edu


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