Sounds almost as if the plate blocking capacitor is bad such that
the tank is only loosely coupling to the tube (that could explain
the weak dip, and the low output power).
Does he have an impedance analyzer like the MFJ-259 that he could
use to check the tank?
Mike, W4EF..............................
----- Original Message -----
From: <nospam4me@juno.com>
To: <amps@contesting.com>
Sent: Tuesday, May 29, 2001 7:38 PM
Subject: [AMPS] care to take a guess..? Alpha problem
>
> -
> 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
>
> ________________________________________________________________
> GET INTERNET ACCESS FROM JUNO!
> Juno offers FREE or PREMIUM Internet access for less!
> Join Juno today! For your FREE software, visit:
> http://dl.www.juno.com/get/tagj.
>
> --
> FAQ on WWW: http://www.contesting.com/FAQ/amps
> Submissions: amps@contesting.com
> Administrative requests: amps-REQUEST@contesting.com
> Problems: owner-amps@contesting.com
>
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|