[Amps] W8ZR Autotune Amplifier Progress Report

Fri Dec 25 17:55:13 EST 2020

I have an 86 in one of my tube amps.  A dual section type. Pulled out 
the detent and use a type 23 direct drive.  Works great; way way more 
torque than needed.

The bigger issue (at least in my thinking) is the method you use to 
determine the switch position.   I used a small belt-driven gear off the 
switch over to a multi-turn pot which is ready by an DAC.

The disclaimer to this is that Jim's build and design quality is way way 
way better than mine.  So I'm only answering the "can it be done that 
way" question.  Not the "yes, I know it CAN be done that way, but SHOULD 
it be done that way?" question...

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com

On 12/25/20 3:34 PM, Gary Schafer wrote:
> I have a switch like that on an old TMC amp. It was very hard to turn to change bands so I put a much weaker spring on it and it turns very easy now. There is a micro switch that gets activated whenever the switch is properly aligned in each detent. I wired that micro switch in series with the PTT line so that you can only transmit when the band switch is precisely set on the proper band. Works great.
>
> 73
> Gary K4FMX
>
>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of
>> Steve, NR4M
>> Sent: Friday, December 25, 2020 3:17 PM
>> To: Jim
>> Cc: amps at contesting.com; amps at groups.io
>> Subject: Re: [Amps] W8ZR Autotune Amplifier Progress Report
>>
>> Good question. I was wondering the same thing.
>> Those switches have a serious detent.
>> Someone who has the resources could partially fill them in
>> with a machine able epoxy.
>>
>> 73 de Steve NR4M
>>
>> Sent from my iPhone
>>
>>> On Dec 25, 2020, at 3:47 PM, Jim <jimw7ry at gmail.com> wrote:
>>>
>>> Question Jim..
>>>
>>> Do you (would you) remove the detent from a Radio Switch
>> band switch? Or will a large enough stepper turn them with
>> the detent in place?
>>>
>>> Thanks
>>> 73
>>> Jim W7RY
>>>
>>>> On 12/19/2020 3:33 PM, Jim Garland wrote:
>>>> Hi all,
>>>>
>>>>      As you probably know, commercial automatic vacuum tube
>> amplifiers have been available for more than decade, but they
>> are expensive; their pricetag adds about $2000 to the cost of
>> a comparable manual-tuned amplifier. For homebrewers,
>> autotune capability is complex and difficult to duplicate, at
>> least for most of us who are not professional design
>> engineers with access to sophisticated workshops. For the
>> past year, I've been working on an autotune control circuit
>> intended to overcome these barriers. The purpose is to make
>> it possible for amateurs with average technical skills to add
>> autotune capability to almost any vacuum tube linear
>> amplifier, whether homebrewed or commercial.
>>>>      Here are the design goals for my controller:
>>>>      (1) The performance should rival that of
>> top-of-the-line commercial autotune amplifiers, (My benchmark
>> is the Alpha 9500.)
>>>>      (2) The controller should be easy to duplicate for
>> amplifier builders with average homebrew experience.
>>>>      (3) The controller should be affordable, costing no
>> more than $100-$200.
>>>> It has taken me a year to realize these objectives, most
>> of which was spent learning to use an advanced, yet
>> inexpensive, microcontroller called the Propeller PX32A. (The
>> PX32A was designed in California by the Parallax Corporation,
>> maker of the popular Basic Stamp controllers) The PX32A is a
>> sophisticated device containing eight fully independent
>> 32-bit microprocessors that share 31 read/write IO ports and
>> a common memory for storing variables, computation results
>> and data. These features make it possible to construct a
>> complete amplifier autotune circuit on an uncrowded file
>> card-sized  printed circuit board using ordinary through-hole
>> components that can be wired up in an evening. The circuit
>> board intelligently operates inexpensive stepper motors and
>> motorized switches to adjust the tank circuits of almost any
>> h.f. vacuum tube amplifier. An ordinary PC or laptop computer
>> programs the device,  but once programmed, no external
>> computer is required. Because of its power, the PX32A
>> implements numerous advanced features while requiring only a
>> handful of additional components.
>>>> Although it has taken me almost a year to write and debug
>> the program
>>>> code for this controller, I 'm finally ready to move the
>> project out
>>>> of the breadboard stage. Here's a link to a YouTube video that
>>>> demonstrates the controller's user features. (My eventual
>> amplifier
>>>> will use an 8877 triode in a conventional grounded grid
>> circuit, but
>>>> that's a topic for another day.) I apologize for the
>> crudeness of the
>>>> video, but hope you find it interesting and will let me know your
>>>> comments and suggestions. (If the below link doesn't work, just
>>>> Google "W8ZR YouTube Prototype Controller" )
>>>>
>>>>     https://www.youtube.com/watch?v=1qDGoEElKcU
>>>>
>>>>     Thanks and 73,
>>>>     Jim W8ZR
>>>>
>>>>
>>>>
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