[Amps] The GU84B and GU78B tubes / some brief history

[Carl]

Ive even run swamped grid old glass triodes without neutralization. 
Currently it is a pair of Class C 6C21's in parallel that runs up to 20M and 
Ive no doubt it would work higher. That amp ran 250TH's earlier.

During the 70-80's I built and sold plenty AB1/AB2 single and dual 4X1 amps 
and never needed neutralization, even on 10M at 5KV.

A swamped grid Class C 4X1 covering 160-10 and driven by a 32V2 is the next 
project for my own use. Guess what tank circuit Im using (-;

Carl
KM1H




----- Original Message ----- 
From: "Vic K2VCO" <k2vco.vic at gmail.com>
To: <amps at contesting.com>
Sent: Monday, October 29, 2012 10:59 AM
Subject: Re: [Amps] The GU84B and GU78B tubes / some brief history


> Why do you say that a swamped grid-driven tetrode needs neutralization? I 
> haven't seen this in published designs. Isn't a 50-200 ohm swamping 
> resistor enough to stabilize the amplifier?
>
> Agreed on the other points!
>
> On 10/28/2012 11:57 PM, Jim Thomson wrote:
>> ##  actually, they are not apples and oranges.  One has an extra grid in 
>> it,
>> requires a regulated screen supply, neutralization, and some method to 
>> cancel out
>> the Xc between the cathode and control grid, so u just cant slap a 50/200 
>> ohm.
>> passive grid resistor in there.
>
> -- 
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco/
>
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