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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