[Amps] AL-80B questions

[Tom Rauch]

> A friend has a TL922A which gave him problems. First it was fried contacts
> on the bandswitch, then a burned out zener bias diode (twice), and finally
a
> shorted 3-500Z. He reported hearing a sizzling/arcing sound on several
> occassions. This all over a period of probably a year or so. We purchased
> and installed AG6K's parasitic supressor kit, without using any of the
other
> parts in the kit. He has not had any problems with the amp in 2 years
since.


You:

1.) Replaced the swicth with a new switch

2.) Replaced a shorted 3-500Z with a good new tube.

Now you don't have a problem, and the amplifier works.

Why am I not surprised?

> And as a caveat to any who might be thinking of doing some work on your
amp.
> I converted my SB220 over to QSK using AG6K's mods. Part of the mod
involves
> removal of the zener cathode bias diode and installing a string of diodes
on
> a board and an optoisolator and switching transistor to replace the
original
> relay. The bias voltage is adjusted by selecting however many diodes in
the
> string that produces the correct amount of bias. Since I had mounted the
> diodes on a board under the chasis, I had the amp laying on it's side on
the
> bench so it could be accessed to make the adjustment. When I powered it
up,
> the fireworks began. Ended up with a burned up grid choke, a couple burned
> up grid bypass caps, some fried diodes on the HV rectifier board. I am
> pretty sure that having the 3-550Z's in a horizontal position was the
> culprit, and the grids probably sagged over and shorted to the cathode.

Maybe the AG6K suppressor kit caused the short, by introducing a VHF
parasitic?

I'd bet if you removed all the mods and replaced the tubes the amp would
have worked just fine, proving the AG6K kit caused all the problems......hi
hi.

It doe not amaze me that people replace bad parts, and problems go away.

73 Tom