[Amps] Comments solicited on AL-82 amp

[Carl]

The AL-82 has had a long history of expensive tube arcs since the Chinese 
3-500's dont hi-pot even close to the Eimacs and they arent gettered as well 
either in production.

Later models added a surge resistor in the HV line to minimize current (and 
damage) until a fuse blows or the event has passed. BUT NOT running the amp 
often enough to get a nice red glow on the anodes will continue to cause gas 
arcs. The getter material is on the anode surface and is activated by the 
heat. New tubes especially need this done for several hours and if you have 
the electronic bias option it defeats the purpose a lot.

The large Ameritrons are also known for opening up a electrolytic equalizing 
resistor and blowing that cap as well as others suddenly letting loose as 
the unloaded HV is always too close to the maximum cap rating to be safe; 
all it takes is a small line surge to go bang.  The exact same PS is in all 
3 big amps.

Adding another cap or two with resistors is fairly easy or just replace the 
PS board with one that is built for Snap In caps and use 8 270uF 500V 105C. 
Mouser and Digi Key carry several good brands. Ameritron upgraded cap values 
several times over the decades and now uses 270uF.

ANOTHER Ameritron problem is the step start fails and the result is often a 
blown transformer. The cause is an unknown number of amps that were 
miswired, and the relay contacts weld shut. Ameritron came up with a fix but 
would not acknowledge that they caused the failure. A few owners got all new 
parts under warranty however; one I know of failed right out of the box. In 
any case none of those AL-82/1200/1500 amps agree with the schematic.

Ameritron no longer uses Dahl transformers and the new ones by Indiana 
Transformer havent been around long enough to get a long term reliability 
score.

I would NEVER run the boost winding on the AL-82 (with added electrolytics 
first) as the chance of 3-500 failures has increased dramatically at 4KV. 
Besides the added power wont be heard at the other end with any of those 3 
amps. The AL-1500 8877 could also get a bit unstable as no parasitic 
suppressor is used and even Eimac tubes have been known to fail at 4KV from 
an internal arc. The small power boost isnt worth it.

Carl
KM1H



----- Original Message ----- 
From: "Ray Day" <rayday at cox.net>
To: <amps at contesting.com>
Sent: Friday, October 24, 2014 11:06 AM
Subject: [Amps] Comments solicited on AL-82 amp


> Hi all,
>
>
>
> Ray N6HE here... I'm in the market for an amp to replace my deteriorating
> SB-220. I love the (2) 3-500 in grounded-grid configuration 
> characteristics
> and am looking for a full legal limit not-too-expensive tube (not solid
> state) amp. I'm aware of MFJ/Ameritron's spotty history with workmanship
> quality and will check out anything from them carefully. I'd rather buy 
> new
> as opposed to used. $3,000 or less is my budget. Have a special 220VAC 
> line
> already run for the SB-220. I've reviewed the eHam Reviews (not much 
> "meat"
> in them) for it but respect the knowledge of this group much more.
>
>
>
> I'd appreciate any comments from members the group with their experience
> (including if there are any odd things to especially be on the lookout for
> when using it) with the AL-82 - and of course any other amp 
> recommendations
> within the parameters above.
>
>
>
> Thanks in advance, 73,
>
> Ray N6HE
>
>
>
>
>
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