After looking over my '77, here's a list of things I'd check.
.. Make sure bandswitch chain drive is in time. (correct
contacts engaged and centered in all switches)
.. Plate blocking cap. (already mentioned)
.. Output vacuum relay. (switching, melted/stuck contacts)
.. Tuned input bypass switch is switched toward the tube. (NOT bypassed)
The last one is a long shot, but if you're driving it with a
broadband rig, you never know.. ;-)
73,
Jim Barber, N7CXI
>-
>Hello there,
>-
>A non amps member, Bob W0YVA Emails me with
>a problem he's having with his just purchased used
>Alpha A77. Care to take a stab with your opinion of
>the problem..?
>-
>I have directed him to watch the amps archive for
>your answers. Below is a copy of his text to me...
>73's-skipp
>-
>[snip]
>: Here is what I have:
>: This is a "new" A77 (looks like never used) -
>: Serial 2556.
>: Seems to be okay except very low power output
>: (200 watts or so) with 80 watts drive. There is
>: plenty of grid current. Applying drive results in
>: significant plate current (800ma or so) which
>: can be dipped (the dip is very shallow) for
>: "max" power. HV reads normal. Power is
>: being measured with Bird wattmeter using
>: 5KW Bird dummy load. Problem appears on all
>: band segments.
>-
>: Here is what I have done:
>-
>: 1. Replaced 8877 with known good tube - no
>: difference.
>: 2. Checked bias directly at 8877 socket -
>: switches properly from high to low with
>: drive applied.
>: 3. The zener, D13, seems okay - checked
>: with ohmmeter.
>-
>: Where is the power going with all that plate
>: current? Weird.
>-
>: Suggestions for what to check? The plate
>: tank components all look good - no evidence
>: of heat anywhere.
>-
>: Any help would be appreciated.
>-
>: 73, Bob
>: W0YVA
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