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From: "Dick" <knaap159@zonnet.nl>
To: <rsgb_lf_group@blacksheep.org>
Date: Sun, 9 Apr 2006 13:25:23 +0200
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Subject: LF: Tech questions  G3YXM amp+18 divider
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Status: O

Hello all,

I'm building a new (and larger) 136kHz transmitter.

The output circuit is the same as the one used by G3YXM with 4 times
IRFP450.

Each FET will get his own gate input resistor (6R8) and gate-to-ground
resistor (47k)
The sources will be grounded as short as possible to ground, while the
drains of
2 FET's will be connected together.

I am now in the stage of putting the components of the output circuit on its
correct position,
and that raised some questions about where to mount what.

I am using a large heatsink 12x15x5cm.
On this heatsink I mounted a 1.5mm thick copperplate 75x150mm in order to
transport heat quick away from the FET's.
Maybe it's some 'overkill' , but I just want to set up a thing that can run
for hours
on full power; just a bit of reserve...........

The 4 FET's are mounted in a row, separation between the FET's is 1 FET
width (abt 15mm).
The resistor of the 'zobel-network' is mounted just in the center , with
wires about 30mm long connected
to the drains of the FET's.

I do not expect problems, but maybe that 30mm is too long???
I don't think I can make them shorter without changing the whole component
layout.

If anyone has experiences with this amplifierstage and the zobel-network
wire length,
I would glad to hear.

Another thing coming into my mind is to set up a fixed frequency into the
transmitter, beside the VXO.
I do have an 4.9152MHz X-tal, but I have to divide it by 18 to get the
necessary 273.066kHz.
Any simple schematic (with easy to get components) for an divide by 18
circuit?

73

Dick, PA4VHF