I'd think it would be better to use a 6dB pad to increase the drive
requirements, so that the exciter always sees a 50 ohm load (neglecting
reactive effects). Basically, one would have a 50 ohm resistor swamping the
grid, and in parallel with that resistor would be a 50ohm and a 100ohm
resistor in series. Drive would be applied at the junction between the 50
ohm and 100 ohm series resistors. A 6dB pad doubles the voltage drive
requirements (4 times the power).
73,
Jim W8ZR
****************
Message: 1
Date: Thu, 9 Aug 2012 14:19:07 -0400
From: "Carl" <km1h@jeremy.mv.com>
Subject: Re: [Amps] 4CX1500B project
To: "Radio WC6W" <wc6w_amps@yahoo.com>, "Vic K2VCO"
<k2vco.vic@gmail.com>, <amps@contesting.com>
Message-ID: <2EAA1432ECE748E089323C74137505BA@computer1>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
The NCL-2000 used just a resistive input of 50 Ohms for as low as 20W drive
for 1200W output which was the tubes limit. Bias was in the -25 to -45 range
(wide mfg tolerances) for AB2 in CW. The tubes are 8122's. The tap on the
resistor network went to 25 Ohms for the typical 100+ watt exciter of the
day.
Carl
KM1H
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