[Collins] 30S-1

[Carl]

I hope you use a dynamic signal to run the IMD tests which better compares 
to real world than a steady state 2 tone.

Carl
KM1H


----- Original Message ----- 
From: "Alan Chandler" <alanchandler at frontier.com>
To: "collins" <collins at mailman.qth.net>
Sent: Monday, September 20, 2010 1:28 PM
Subject: [Collins] 30S-1


> The 30S-1 is one of the lowest IMD amplifiers ever produced for amateur 
> use.
> It uses a grounded screen grid and operates the cathode at about -200 
> volts
> as the screen supply.  The RF drive is supplied to the cathode so the RF
> adds about 100 volts to the cathode which results in a total screen supply
> of about 300 volts when fully driven.  The Eimac 4CX1000A maximum screen
> voltage is 400 so adding 125 volts to the screen supply will exceed the 
> maximum rating under RF drive.  Typical AB1 operation for the 4CX1000A is 
> with 325 volts on the screen which is about where the 30S-1 actually 
> operates.  Increasing the screen voltage does increase the gain of the 
> tube, requiring less drive power but it reduces the available plate 
> voltage swing before the screen current rises to the level that exceeds 
> the screen dissipation (35ma at 325v is just under 12 watts,
> the maximum screen dissipation.)  and the tube is in saturation. The net 
> result can be more output power but with a substantial increase in IMD. 
> You will typically get about 1 to 2 dB increase in power (0.2 to .04 S 
> units) and about 10 dB higher IMD (2 S units).  Be kind to operators on 
> adjacent frequencies and leave the screen supply where it was designed to 
> be operated.
>    I have just about finished setting up a variable screen supply and will
> make power and IMD measurements with a 4CX1000A and 4CX1500B in a 30S-1 
> later in the fall.  I started the project in the Spring but good weather 
> forced yard work to take precedence.  When I complete this, the results 
> will be sent to The Signal.
>
> 73, Alan - K6RFK
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