>Hi gang,
>
>I'm a newbie when it comes to working on amps and would like some
>suggestions/advice. Here's the situation:
>
>I recently acquired an AL-80A which appears to be cosmetically good and
>complete. When I fired it up, the plate and grid current appear to be
>fine. However, the plate doesn't "dip"
? when loaded properly, there is very little "dip" in a linear
amplifier's "plate'/anode current.
>and applying any significant drive
>to the amp results in "hissing" or "sparking" noises and of course zero
>power out.
>
>Any ideas as to what may be wrong and where to start?
>
? For starters, I would inspect the bandswitch and the Tune-C with a
dental mirror and a penlight, paying especially close attention to the
15m and 10m coil contacts, plus the 160m and 80m Tune-C padder contacts.
Arc marks on the variable Tune-C plates and/or toasted switch contacts
could be an indication of parasitic oscillation - or a very serious
fruit-fly infestation. // Parasitic-oscillation is due to the
tube's/tubes' not-insignificant internal feedback-C (0.3pF for 2,
3-500Zs; 0.7pF for 1, 3CX1200A7).
have phun, Mike
>
>
>
>
>
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