[Amps] AL-80 (early) Loading control at full C

[Tom Rauch]

> I'm the recent proud owner of an early (SN 151) AL-80. 
> After reworking the power supply, I finally have it 
> running (sort of). Latest 'issue' is the Loading control 
> seems to be at or near full C (max CCW) position on 160, 
> 80, 20 meters (haven't checked the others). It does make 
> 500 watts CW out. I notice there is a modification to add 
> ~10 diodes in series with cathode, I guess to reduce 
> idling current and move towards AB1. Plate circuit looks 
> good, no burns or scorch marks. Bandswitch looks 
> excellent, as do doorknb caps on loading side.
>

Tony,

I don't want to make you unproud, but the AL80 was full of 
problems. That amp was designed by Ameritron when Denny from 
Amp Supply owned it. I inherited that mess when, as part of 
a debt cancelling, Prime Instruments assumed control of all 
the assets of Ameritron. (Prime had initially funded most of 
the operation and owned most of the tooling and parts.) I 
was hired by Prime to get Ameritron going so they could 
recover some of their investments.

John Moran W8IOB owner of Prime and I reviewed the AL-80 
design because it was almost impossible to build, had an 
exceptionally high failure rate, and generally did not work 
well. The original problems includes wrong component values, 
poor cooling system design, a idiotic QSK system that was 
copied from or based on a low power Heathkit 2 meter amp, 
inadequate tube anode-to-case clearance, seals on the tube 
over temperature even when RF wasn't applied, safety 
hazards, and so on.

Ameritron took it on the chin and paid to strip all the 
original amps down to bare metal and rebuild them at no 
charge. The cooling system was heavily modified, the tube 
socket lowered, the tank components tossed out and replaced 
with correct value components, the tuned input corrected, 
resistors across the power diodes removed, the QSK system 
removed, resistors across the electrolytics removed and 
replaced with proper parts, new HV multiplier resistors 
instead of ones purchased at a surplus store (they had 
chronic failures), new meter that reads 300mA grid current, 
filament voltage lowered, an actual wiring harness instead 
of point-to-point, different metering, different bandswitch 
(non-shorting with pick-up-and-hold rotor and different 
contact layout), and so on.

Original units started at 100 and went to around 200. They 
were supposed to be renumbered when rebuilt at the factory. 
When existing field  units were rebuilt or new ones released 
they were assigned a S/N of 300 and higher. New units with 
more mods were 500 and higher.

I'm not sure what level you amp is at but:

1.) Look at the resistors across the electrolytics. They 
cannot be brown colored carbon resistors. They must either 
be gray 100K metal films or something equal.

2.) There must be cooling holes in the chassis below the LF 
tank coil on the phenolic form, and there must be additional 
vent holes added at the chassis front.

3.) The fan must be a slow speed fan like a TA450S without a 
speed slowing resistor. The ~400 ohm resistor originally 
used must be removed. If you don't do these mods the seals 
in the 3-500 will run over temperature even without drive.

4.) The tube socket must be the minimum height possible so 
the anode clears the cover by as much as possible.

5.) The resistors across the rectifiers must be removed.

6.) If you have a black painted QSK module, it has to be 
disconnected. Failure to do that can ruin your transceiver.

As for your tuning issues, the reason the loading control is 
fully meshed is the tank components are all wrong. There 
isn't enough inductance on most bands. I'm not sure how you 
would fix that now. Ameritron scrapped the original huge ~3 
inch diameter #8 coil and rewound it about 1.75 inches 
diameter with more turns. The pair of Centralab 200pF 
padders for 160 tuning were changed to HEC 170 pF.  The 
phenolic coil for low bands was rewound with more turns, and 
the padding capacitors for the loading all changed.

As soon as possible the AL80A was put in to replace the 
AL80.

Sorry for the bad news, but Ameritron made a effort to 
contact anyone who filed a warranty card on an original amp 
and rebuild it for free at Prime Instruments expense. I 
wouldn't touch one unless it was over S/N 300.

73 Tom