[Amps] AL-80B questions

[rlm]

>> 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?
>
** Because you left something out?

>> 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

-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K, 
www.vcnet.com/measures.  
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