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

[Roger (K8RI)]

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 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/
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>> -----
>>> No virus found in this message.
>>> Checked by AVG - www.avg.com
>>> Version: 10.0.1427 / Virus Database: 2441/5361 - Release Date: 10/29/12
>>>
>>
>