[AMPS] New AL-82 problem...

[Dave Hockaday]

I bought a new AL-82 about 2 weeks ago. Nice looking amp. I was going to
install the 10 meter mods, but when I contacted Ameritron, they requested a
copy of my license and a written description of my desire to operate it on
10 meters via US Mail...so I  assembled it without the mod. 

A couple of nights ago, I was on 40m CW (I think, though I may have been on
ssb trying to work the ZK1). A loud "SNAP!" came from inside the case. The
amp continued to work OK, but now my idling current is up to 325 ma. (from
the normal 75ma CW/150ma SSB). The plate voltage is about 3500vdc unloaded,
and about 3300vdc loaded, exactly as it was when I first powered it up. The
SSB/CW switch has absolutely no effect on the idling current, it stays at
325ma while the amp is keyed with no drive. 

The rig I use with this amp only drives it with about 80 watts. After the
"SNAP!", the power output of the amp seems to have increased a little. What
could have failed?

Wow...The amp is only 2 weeks old. 

I studied the schematic a bit. I don't think the problem is in the metering
board, especially since the current doesn't change when the CW/SSB switch is
toggled. I guess it's possible that the zeners (ZD1 and ZD2) could have
failed, but isn't it unlikely that they would both fail at the same time? If
the Zeners failed, wouldn't that indicate some sort of momentary arc-over in
one of the tubes??

Thanks
Dave WB4IUY
wb4iuy@ipass.net


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