On 10/29/2012 11:34 AM, Vic K2VCO wrote:
I presume you mean the modified B&W 852!
I remember two different models from B&W. One was the standard 850A(?)
with a "stepped" coil. A lower frequency portion of about #8 wire, (80
and 40m) followed by something on the order of 1/4 " or 5/16" tube, (20
and 15m) and then a flat strap coil (10 m) mounted on top of the end
ceramic/band switch. The second unit just consisted of about 5/16ths
tube. I don't remember if that one had the strap coil on the end or not.
73
Roger (K8RI)
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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