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

[Vic K2VCO]

The one I plan to use is marked '852' and is the low-impedance version with the whole coil 
made of 5/16" tubing. It has the external 10m strap coil. There is also an 850A (I have 
one in poor condition) which has the "miniductor"-like low-frequency section. They made 
one called the 850/160 which had a 160m section. I haven't ever seen one of those in the 
flesh. There is also an 851, which is a lower-power version.

On 10/29/2012 12:31 PM, Roger (K8RI) wrote:
> 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/
>>>>
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>>>
>>
>
>
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-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/