[Amps] AL-80B questions

[Skram, Helge (MED)]

Hello 

I have an AL-80B amp, purchased some years ago with a problem. The first
owned said it had popped and developed resting current when keyed (may have
been 250mA). It was sent to service and the zener that sets bias was
replaced. The original Amperex 3-500Z was reportedly gone and a new 3-500Z
from Pride was purchased. Then I got the amp.

Before I put in the new Pride tube, the amp was inspected and found to my
surprise that the amp cover was still with masking tape ! When Ameritron
paints the cover it is masked with paper tape where it it supposed to
contact the amp chassis. It is then normal practice to remove tape before it
is used on the amp chassis. Not so with my amp !
I guess there was a shielding anomality of the RF compartment in my amp,
that may have contributed to parasitic oscillations. Anyway the tape was
removed and the AL-80B have worked very fine for several years and contests.


Ameritron was not contacted, since the first owner purchased it in Texas and
brougth it back to Norway.
The remaining masking tape was easy to fix.

Check that there is no tape on the underside of the AL-80B top/side cover.


Regards

Helge Skram
LA6MV



-----Original Message-----
From: ad5gb [mailto:ad5gb at myway.com]
Sent: 2. mars 2003 06:18
To: amps at contesting.com
Subject: [Amps] AL-80B questions



Greetings amps gurus,

A friend of mine just called me. He bought an AL-80B about 6 months ago.
It's now eaten it's 4th tube. He's sent the amp back once and gotten
replacement tubes the other times.

This morning he wanted to try to work some of the contest on 10M, began
tuning up, said he heard a little "tick..... tick-tick" and then no output.
ZSAC is about 250mA.

The other times this happened he said Ameritron told him that they'd gotten
a bad batch of tubes (Amperex) and exchanged them for him.

The one time that he sent the amp in to Ameritron they said they found
nothing wrong.

Having never experienced parasitic problems first hand I can't speak from
experience but the last time this happened I suggested that he try one of
Rich Measures' retrofit kits. He says he now has it but hasn't installed it
yet.

My questions:

1: Does this sound like a symptom of parasitic oscillations?
  I thought the 3-500Z was pretty rugged with respect to faults.

2: Does anyone know of any problems with recently built Amperex bottles?

3: I'll probably help him install the parasitic supressor kit somethime this
week.  Are there any other things to look for or suggested corrections to
this thing that would make it less prone to eating another tube?

Thanks in advance all!


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