[Amps] Tube Class C operation no Drive power or grid current

[sm0aom at telia.com]

You are not required to drive the tube into the grid current region in a Class-C amplifier.

The definition of Class C operation is a current flow angle of less than 180 degrees, which
is accomplished by biasing the control grid beyond plate current cutoff. There might be a differentiation between
Class C1 and Class C2, similar to Class AB1 and AB2.

"Greatest efficiency is obtained when the input drive to the grid of a Class C amplifier is sufficiently high to allow grid current to flow during the more positive parts of the positive half-cycles. This is the method of working most commonly used and can be referred to as Class C2. If grid current does not flow, the mode of operation may be described as Class C1. References to RF power amplifiers normally state Class C, whereupon Class C2 operation can usually be assumed". 

I believe that "Taschenbuch der Hochfrequenztechnik" goes into more detail about this.

As the tube is more efficiently used with grid current or Class C2 it is usually tacitly assumed that all Class C operations use grid current.

Regarding suppressor grid modulation, it is a quite simple and inexpensive way of obtaining AM without using an expensive and heavy Class B modulator. It had a brief popularity in mobile AM gear, especially ship's radio transmitters, before WW2 in Europe.

It shares its downsides with other forms of grid modulation which primarily are low carrier efficiency and being somewhat difficult to adjust.

In larger suppressor-grid modulated transmitters, an oscilloscope for proper modulation adjustment was often included.

73/
Karl-Arne
SM0AOM


 

----Ursprungligt meddelande----
Från : wlfuqu00 at uky.edu
Datum : 2022-10-09 - 00:14 ()
Till : dj7ww at t-online.de, amps at contesting.com
Ämne : Re: [Amps] Tube Class C operation no Drive power or grid current

Note:
Zero drive and grid current is only with 3kV plate voltage and as CLASS-C Oscillator or Amplifier. (CW, FM, PM)
Notice not the same for 2kV plate voltage but same efficiency.

73
Bill wa4lav
________________________________
From: Fuqua, William L. <wlfuqu00 at uky.edu>
Sent: Saturday, October 8, 2022 6:09 PM
To: Peter Voelpel <dj7ww at t-online.de>
Subject: Re: [Amps] Tube Class C operation no Drive power or grid current

I was discussing two separate things.
One was Class C CW Oscillator or Amplifier operation

The second was advantage and disadvantages of Suppressor grid modulation.

73
Bill wa4lav
________________________________
From: Peter Voelpel <dj7ww at t-online.de>
Sent: Saturday, October 8, 2022 2:54 PM
To: Fuqua, William L. <wlfuqu00 at uky.edu>; 'Amplifiers' <amps at contesting.com>
Subject: RE: [Amps] Tube Class C operation no Drive power or grid current

CAUTION: External Sender


The RCA data sheet shows the opposite:

https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Ffrank.pocnet.net%2Fsheets%2F049%2F4%2F4E27.pdf&data=05%7C01%7Cwlfuqu00%40uky.edu%7C0348c5c8fcc44d31881f08daa95e98de%7C2b30530b69b64457b818481cb53d42ae%7C0%7C0%7C638008521428471840%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C2000%7C%7C%7C&sdata=zUk2wvKkRV7pzkCh4f8LNimqb7TU89kHLo9D%2Fb0VMsk%3D&reserved=0

73
Peter, DJ7WW

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Fuqua, William
L.
Sent: Samstag, 8. Oktober 2022 20:38
To: Amplifiers
Subject: [Amps] Tube Class C operation no Drive power or grid current

    Maybe I have not looked at the data sheets very closely , but I was
surprised to find a medium power glass Pentode that required zero grid
current, thus no drive power in class-C operation.  The 4E27, not the A
version

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