[Amps] 1:9 un-un for grid driven tetrode

[Carl]

The National NCL-2000, ca 1964-70
used a pair of 8122 tetrodes with an untuned resistive input.

The bias was AB1 on SSB and AB2 on CW where grid current was used.

Carl




----- Original Message ----- 
From: "Peter Voelpel" <dj7ww at t-online.de>
To: "'Rob Atkinson'" <ranchorobbo at gmail.com>; <amps at contesting.com>
Sent: Sunday, October 24, 2021 10:47 AM
Subject: Re: [Amps] 1:9 un-un for grid driven tetrode


> That 1:9 unun and 450 ohm resistor is obviously for use with a high power
> linear tetrode amplifier.
> Passive grid would not work with grid current.
>
> Tetrodes requiring a few hundred volts of drive are for instance 4CX10000 
> or
> 4CX15000 and similar
>
> 73
> Peter, DJ7WW
>
> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Rob Atkinson
> Sent: Sonntag, 24. Oktober 2021 13:19
> To: amps at contesting.com
> Subject: [Amps] 1:9 un-un for grid driven tetrode
>
> The unun is (my opinion) a waste of time.  Just connect your grid
> input network, usually a pi network for tetrodes, to the grid and
> design it to do all the impedance transformation.  It can be band
> switched and you'll be fine.  I don't know what tube this is but its
> data sheet should give you the driving peak RF grid v.   You also
> didn't specify the class of operation, but for class C the grid has to
> be biased around 5 times past cutoff.   The data sheet should have
> "typical operating" specs for a certain plate v. and operating class.
> Divide the peak RF drive v. by the grid current given for the class of
> operation.  That will give you the grid impedance.   Construct a "grid
> dummy load" of carbon resistors that are close to the grid Z value and
> connect them from the grid socket lug to ground.  Now you can put a
> vswr analyzer on the RF input jack and futz with your input network to
> get it in the ballpark to get the grid Z to 50J0.   To get the drive
> needed, multiply the peak RF grid v. by grid current.   You can get
> the needed grid current by dividing the peak RF v. by the grid Z.
> Tetrodes usually do not require a lot of drive compared to triodes.
>
> 73
> Rob
> K5UJ
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