Hi Carl & All...
RE: the query in your posting headed as shown at the end of my note, the
ALPHA 91B uses modest unbypassed resistance in the cathode lead (12 ohms or
so I think) to create a few dB of rf negative feedback (1) to improve
linearity so IMD is better than most, if not all, modern ham xcvrs, and (2)
to set the nominal gain to comply with FCC type acceptance requirements.
We did have to provide very good screen bypassing - an ordinary ceramic
socket with common disk caps (very short leads) bypassing the screens left
us with "difficulty" (which may be understating it - I don't remember all
the details) in absolutely preventing VHF/UHF parasitics. Our basic
criterion is that, under all test conditions (including those which others
recommended here recently - low bias, near-maximum dissipation, no drive)
the amp MUST NOT show any sign of instability at any frequency & under any
combination of adjustments, unless the output is connected directly back to
the input externally. The latter is an operating condition which we
heartily recommend against(!) and do not ordinarily attempt ourselves.
73, Dick
-----Original Message-----
From: km1h@juno.com [SMTP:km1h@juno.com]
Sent: Thursday, May 14, 1998 7:16 PM
To: amps@contesting.com
Subject: Re: [AMPS] filament decoupling for RF
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