73, Tom W8JI
----- Original Message -----
From: "Mike(W5UC) & Kathy(K5MWH)" <w5uc@cox.net>
To: "Tom W8JI" <w8ji@w8ji.com>; "AMPS" <amps@contesting.com>
Sent: Monday, July 24, 2006 7:54 AM
Subject: Re: [Amps] Pi network tuning
> Good Morning:
>
> The tubes are Gi-7b's. (output capacitance = 4.6 pf/tube)
> The grids are tied hard to the chassis. I cut holes in
> the chassis just big enough for the grids to fit through,
> and then made clips (3 per tube) similar to those used to
> mount 4CX250B tube sockets. (no grid fuses here HI). The
> strap from the anodes to the blocking capacitors is brass
> (tinned at the connecting points) about 1/4" wide and
> approximately 1.5" long.
All sounds good. If the tubes have conical grid supports and
very low lead length it should be very stable. You probably
won't even need a suppressor if the grids are compact with
short wide connections.
>The plate capacitor is a standard air variable.
There's the rub. You not only have stray capacitance to
contend with, series inductance increases the effective
capacitance even more.
Did you look at the estimated capacitance required compared
to the tube output capacitance? I've never used that tube so
I don't know what typical output C is.
73 Tom
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