I presume you mean the modified B&W 852!
** Its an 850A that Ive rebuilt and slightly modified the L values. The 4X1
is a Hi Z tube
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.
** Its been ages since Ive seen one but I dont remember any special place to
hang a cap. They just added the contact and a modified coil. Im using a
toroid for 160.
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.
** In the past Ive used a WW2 BC-375 switch for padding when I didnt have a
big enough vacuum variable. This time around Im using a 2500pf version that
Ive been hoarding for 20+ years.
Carl
KM1H
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
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http://www.qsl.net/k2vco/
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