Dave,
The idle grid current should 25mA/50mA (CW/SSB). It sound like you
blew one of the zener biasing diodes (ZD1 or ZD2). That can happen
if a tube arcs or also if you transmit before warming up the tubes
sufficiently. Yes, I know 3-500Z no warm-up required... I say
"whatever" to that. My AL-82 will blow a zener pretty consistently
if I don't warm it up. The two diodes are in series and ZD1 gets
shorted when the switch is in SSB position, which provides the higher
bias current. Since the current is high in both switch positions, it
sounds like you blew ZD2. You can continue to use the amp for SSB
but keep the switch in the CW position until you replace it. If you
put the switch in SSB, the tubes will get hot because of too much
bias. Good luck. They are easy to replace and available at
RFparts.com for half of what Ameritron charges. They are 7.5V 10W
Zeners, P/N 1N2971A.
Joe
N1FCJ
At 11:02 AM 12/29/2009, you wrote:
>Happy New Year, all:
>
>On a 7- or 8-year-old AL-82 I just tested, I noticed that, with the amp's
>relay pulled in, but no drive applied, the grid-current meter showed
>50-70mA upscale, all bands, and zero with the
>relay de-energized. There was no
>r-f output.
>
>With drive applied, it has full output on 160-10M, with normal grid
>(upscale) and plate currents.
>
>The resting plate current responded properly to the c-w/ssb switch setting.
>
>The manual says nothing about "resting" grid current, only resting plate
>current.
>
>Anyone out there have any ideas about what's going on?
>
>Tia and brgds,
>
>Dave, W8FGX
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