[R-390] 3DW7: A 3TF7 Tubester

[Miguel Bravo]

Oh!, and thought they had done it before with just an iron wire. At least I
can understand the way the iron wire work.

Merry Christmas / Happy holidays

Miguel

----- Original Message -----
From: "David Wise" <David_Wise@Phoenix.com>
To: <r-390@mailman.qth.net>
Sent: Tuesday, December 24, 2002 10:25 PM
Subject: RE: [R-390] 3DW7: A 3TF7 Tubester


>
> If the input to your pass device is other than DC,
> you must measure true-RMS.  Those "clipped sinewave"
> designs won't work without it.  Another idea is a
> saturable reactor.  It's simple but way too big.
>
> My first try used a forward phase-controlled triac,
> with a light bulb and photocell as RMS sensor.  I
> synchronized the control to the sine wave, using
> an exponential ramp circuit of my own invention.
> (At least, I haven't seen it anywhere else.)
> This was marginally usable, but the light bulb kept
> drifting.  Eventually I gave up on it and found an
> RMS converter IC.  This worked great, but my
> suspicions about RF noise were confirmed.
> I changed to reverse phase control with controlled
> fall time.  This doesn't put any detectable noise
> into the receiver, but the parts count is high.
> Even so, I was able to squeeze! it into the available
> circuit board space to confirm it could be done.
> That was months ago, when I first considered
> announcing the 3DW7.  At that point it would
> have been an analog design.
>
> Dissatisfied with the density, I took the digital
> leap and breadboarded up a microcontroller.
> After months of "interesting" evenings debugging,
> I got the program working really well.  It uses
> power mosfets switched at zero-cross to stay quiet,
> adjusts to voltage changes in one half-cycle without
> overshoot, and (like its analog predecessor) powers
> itself when not conducting, making it a two-terminal
> device.  It factors its own power usage into the
> computed load current.  It senses overloads and
> short-circuits, so quickly that no fusing is required.
> I don't have the facilities to test it, but I think
> it will regulate ugly-shaped, frequency-varying
> waveforms like what you get from a generator or inverter.
>
> It needs neither ground nor shield.  The main heat
> source is the current sense resistor.  It has recessed
> Up and Down buttons on top for calibrating between
> 270mA and 320mA, and stores the setting in eeprom.
> I'm figuring on a transparent plastic envelope.  No I
> will not blow glass :-)  And sorry, it doesn't glow,
> takes too much power.
>
> This design could be adapted to a variety of
> voltages and currents.
>
> Regards,
> Dave Wise
>
>