If there is a problem with the metering circuit as you suggest,
Tom, whereby the grid meter is partially indicating plate
current, then shouldn't the amp be reading some grid current
under conditions of zero drive due to ZSAC?
Mike, W4EF..........................
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: <amps@contesting.com>; <nospam4me@juno.com>
Sent: Saturday, June 02, 2001 5:08 PM
Subject: Re: [AMPS] continued Alpha work
>
> Skipp,
>
> > I've relayed to Bob about checking the blocking caps
> > and the tank alignment. He has done said with no
> > positive results. Here is his latest text to me. I'm in
> > the process of relaying some of the amps members
> > posts back to him.
>
> All of that is a waste of time, if indeed he has high grid current AND
> high plate current at the same time.
>
> Open blocking caps cause low plate current and high grid current.
>
> Misaligned tanks cause low plate current and high grid current, or
> high plate current and low grid current.
>
> High grid current comes from a lightly loaded plate circuit----one
> running the tube into a much HIGHER than desired load
> impedance.
>
> High plate current with a shallow dip comes from running the anode
> into a LOWER than desired anode load impedance, and that
> means you can't have excessive grid current.
>
> When you see high plate current and high grid current with a
> shallow plate current dip as you indicated, it is a dead-giveaway
> the metering system is messed up.
>
> If the metering system is messed up and he is trusting it to tune
> the PA, that explains why the output is low. More than likely the
> grid meter is partially reading plate current through a fault in the
> from the B- return to the chassis. When that condition exists, the
> user will "overcouple" the PA because he "thinks" the grid current
> is higher than it really is.
>
> When he overloads the amp to reduce grid current, he will have low
> output, a shallow plate current dip, and at the same time the grid
> meter will (because of the fault) show excessive grid current that
> really isn't there.
>
>
>
>
>
> 73, Tom W8JI
> W8JI@contesting.com
>
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