[Amps] Negative feedback passive input tetrode

Glen Zook gzook at yahoo.com
Thu Dec 14 17:03:27 EST 2017

The later 30S-1 amplifiers used the 4CX1500 tubes and a number of the earlier units have been updated to the 4CX1500 tubes.
The 3, or 4, depending on who you asked, 30S-3 amplifiers used the 4CX1500. Glen, K9STH 
Website: http://k9sth.net

      From: "Fuqua, Bill L" <wlfuqu00 at uky.edu>
 To: RCM <robrk at nidhog.net> 
Cc: AMPS submit <amps at contesting.com>
 Sent: Thursday, December 14, 2017 2:34 PM
 Subject: Re: [Amps] Negative feedback passive input tetrode
  The 30S1 is biased cathode driven 4cx1000a.  The negative feedback is to the control grid and is a voltage divider between plate and control grid. The 30L1 was neutralized so that it would work properly on 10 meters.

It used an air core transformer and variable capacitor between input an and plate. Have to look at the schematic, but the parallel 811A tubes did not work well at higher frequencies.

  Being that I a looking at grid driven it is a bit of a different story. Neutralization of a grid driven amplifier prevents tuned-grid tuned-plate oscillation.

    Yes, the cathode resistor is the easiest method indeed.


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