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

[Vic K2VCO]

I presume you mean the modified B&W 852!

That's what I'm planning to use for my 4CX1000A amplifier. I simply lifted the strap from 
the cold end of the coil so I can insert a 160m coil. The one thing that I couldn't figure 
out how to do was to add a contact in the 160m position to switch in an additional 
capacitor across the loading capacitor. The rotor wiper for the B&W switch interferes with 
one of the contacts no matter where you position it.

I know B&W made a version of the tank that supported 160m. I bet they used a narrower 
rotor wiper.

I am probably going to gang a small rotary switch with 60 degree indexing to the B&W tank 
and use it to operate relays for the grid coils and the loading padder.

On 10/29/2012 8:23 AM, Carl wrote:
> 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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>

-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/