[AMPS] AL-1500, AL-82, AL-1200, QRO???

[Andy Cook, G4PIQ]

Rich wrote :

>Did the amplifier that shorted the 3cx1200A7s have a glitch resistor. ?
>Who made the amplifier?

Yes. The amplifier is a Henry and has a 25 ohm resistor (+ diode) in the 
path between the -ve side of the filter capacitor and ground.


Tom wrote :

>The 3CX1200A7 is probably the most reliable tube out there.
>Failures are very low. It is also one of the least stable, has high
>internal capacitance, and is moderately hard to drive. That's the
>tradeoff.

This may well be true - it seems a solid tube with high grid dissipation 
capabilities and no issues with a big glass vacuum, but I'm just speaking 
as I've found. I can't say why the first tube failed - the PA was like that 
when bought used. The second one failed around 5 years later following a 
contest where we had a power outage which . At first you'd just see a 1 
second kick on the grid and anode current meters at turn on, and then 
eventually (4 contests or so later) it just went ping.

Andy




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