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@gmail.com>
To: <amps@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/
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