[Collins] 30S-1

[David Knepper]

FYI - this test was conducted several years ago and appeared in an early 
issue of the Collins Journal prepared by Warren Bruene.

David Knepper, W3CRA/W3ST
Editor of the Collins Journal
Secretary of the Collins Radio Association
www.collinsra.com
Join today
----- Original Message ----- 
From: "Carl" <km1h at jeremy.mv.com>
To: "Alan Chandler" <alanchandler at frontier.com>; "collins" 
<collins at mailman.qth.net>
Sent: Monday, September 20, 2010 3:47 PM
Subject: Re: [Collins] 30S-1


>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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