> my al-80A hicuped tonight. I do not have the schematic for this amp.
> It does not show HV now. After inspecting the meter, the reading was
> open from the outside terminals. i have removed the meter from the
> chassis and disasembled. Inside the meter is a small 1/8 or 1/16 watt
> resistor in seris with the meter coil. This resistor reads open. The
> meter coil reads around 400ohms and also the volt ohm meter deflects
> the meter upward about 20%. What is the value of this resistor inside
> the plate, HV, Power, alc meter. ? Also the plate current shunt
> resistor is blown. I also need the value for that.
Look in the manual. Although I designed that amp and managed the
company that built those meters, I can't recall the exact meter
resistances. I think they are 450 ohms, and if that is correct the
resistor would be a hand selected 39 to 68 ohm resistor that makes
the movement read exactly the resistance specified.
With a 0.6 ohm shunt and a 1mA movement, that would be 450 ohms for
750mA full scale. Don't get ANYTHING trashy in the meter, and make
sure you do not splash flux beads in the meter when soldering.
>> Any other thoughts what went on. And how to make preventative
measures
> for the future.
Any number of things could have arced Victor. The tube could be
getting bad, and flashing over. The dirt could have flashed.
You must have an old AL-80A that does not have the HV fault diode
from the supply rail to ground. You need to add that diode, two
capacitors, and a small RF choke. Then a HV flashover will not hurt
anything.
I would not worry about adding any gimmicks to the amplifier, the
suppressor in it is fine. Amplifiers that are not stable do not last
perfectly for 15-20 years, and then suddenly need major modification!
Virtually 100% of the time the problem you saw is either caused by
dirt from poor maintenance or a defective component, most often the
tube.
73, Tom W8JI
W8JI@contesting.com
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