Autek WM1 watt meter

[WA2ROC]

I just picked one of these up from "YOU-KNOW-WHERE" and hooked it up to my Apache and Heath 2040 tuner.  It seems to work great and easy to minimize SWR.  Output power indicated is in the neighborhood of 110 watts, which sounds reasonable. (Apache generates one watt per pound!)

When switched to Peak position, and during normal QSO conversations, the peak power is reading in the neighborhood of 350 to 400 watts.  I think that's what it's supposed to read, 4X the resting output.

Am I understanding this correctly or does the Autek just give the user a false sense of power security?

[W2VW]

My WM-1 reads fairly closely to what I see on an envelope display for peak power with voice and test tone.

[k4kyv]

I'm not sure how critical an indication you are trying to use the meter for, exactly, but for proper modulation and making sure you have a clean signal, a more meaningful indicator would be to set up an oscilloscope for trapezoid pattern in order to observe modulation linearity, by sampling the rf output to the vertical plates, and sampling the audio output of the modulator to the horizontal plates (see an older ARRL or Radio handbook for details). Then switch to envelope pattern to check for flat-topping or other waveform distortion. With nothing more than a Hammy Hambone "power" meter (really an rf voltmeter with the scale calibrated for watts delivered to a 50Ω load), for all you know, you are seeing positive peaks resulting from the final taking off into parasitic oscillation.

Been there, done that.  Once I even had a problem with the modulator going into self-oscillation on voice peaks.  On the envelope pattern, the positive peaks had what looked like hair growing on them, and I was getting signal reports that my signal was splattering.  I cured the problem by placing a 100Ω 10W carbon composition resistor in series with each modulator plate lead, right at the plate cap.

The same goes for a broadcast type modulation meter that flashes at modulation percentages exceeding pre-set peaks.  A useful instrument that doesn't tell the entire story.

But for casual observation that everything in the transmitter is working close to normally, your meter sounds OK.

[WA2ROC]

Thanks for the comments.  I just wanted to see if the claims made by Autec were honest, which they seem to be.

I may get another one, maybe a new one with illuminated meters/

OOOOOHH!

[K1DEU]

Have owned an Autec for many years quite accurate with a triangular wave also. Have enjoyed comparing it to many LED peak reading devices and my various scopes of many different radian delays.  73  Dr. John  K1DEU

[K5UJ]

<<I cured the problem by placing a 100Ω 10W carbon composition resistor in series with each modulator plate lead, right at the plate cap>>

AH HA!  SO, That's why the plates of the 807s in my HT-20 have carbon resistors connected to them!  Except someone put a wire wound job on one which I figured was a boo boo. 

[KF1Z]

The Autek works good.

But, is very very difficult to get compensated to read correctly at say 75 meters, and the higher bands 15m and up.

I gave up on mine and threw it out in the shop...

[KM1H]

A wire wound works fine for an audio parasitic.....aint no RF getting out thru the mod iron.

[k4kyv]

Give me an old buzzard style thermocouple RF ammeter any day.  They read REAL r.m.s. antenna current!

[W2VW]

A wire wound works fine for an audio parasitic.....aint no RF getting out thru the mod iron.

Must me the nickelchrome.

[KM1H]

Does anyone have a WM-1 main board full schematic?

Carl

[KM1H]

[quote A wire wound works fine for an audio parasitic.....aint no RF getting out thru the mod iron.
[/quote]

Must me the nickelchrome.
[/quote]

Yep, pure voodo science at work.

[W2VW]

The audio parasitics I've seen were ultrasonic and occurred only on program peaks. Not the same as a parasitic in a typical H.F.R.F. amplificator where it takes off and keeps going.
A look at old broadcast tx schematics and parts lists would be a good way to decide what works and what doesn't.
I've killed them by swamping the grids too before I knew what I was doing.

[KE5YTV]

I've also just picked up a WM1. Does anyone have a manual they can post? I can't find one on the internet. Thanks for any help.

Mike

[k4kyv]

The audio parasitics I've seen were ultrasonic and occurred only on program peaks.

That is exactly what happened in my case. Those peaks can appear as a few points of additional modulation percentage on a peak reading modulation or power meter.  The meter just measures total voltage and can't tell the difference.  The additional voltage caused by the ringing of the audio components adds to the normal output from the modulator right at the crest. Mine made the tops of the envelope peaks look fuzzy and out of focus on the scope display, but when I set the sweep frequency as high as it would go, I could see the ultrasonic waveform of the oscillation superimposed on the crest of the modulation envelope.

Not the same as a parasitic in a typical H.F.R.F. amplificator where it takes off and keeps going.
A look at old broadcast tx schematics and parts lists would be a good way to decide what works and what doesn't.
I've killed them by swamping the grids too before I knew what I was doing.

Sometimes the rf parasitic may ignite only when the plate voltage reaches a certain level.  It may appear stable without modulation, but as soon as the modulation voltage drives the plate further positive, it takes off, but the negative modulation peak kills it until the next positive peak  comes along.  That can make for some really nasty looking and nasty sounding waveforms and splatter.  A SSB linear may kick into oscillation on voice peaks, even though the DC plate voltage is steady, much in the same manner of the ultrasonic parasitic in a modulator.

I got the idea of the 100Ω noninductive resistor in the modulator plate circuit from the schematic of a 1930s broadcast modulator using a pair of 849s driven by a pair of 845s.  I found a couple of the resistors in the junk box, tried it and it worked. WW resistors might work just as well.

Another Idea I have seen is to cross-neutralise the push-pull modulator stage, just as you would a push-pull rf amplifier.  One suggestion is to use a piece of RG-8 or RG-11 coax as the capacitor, trimmed to length, but an ordinary rf type variable capacitor for the purpose that would be used with an rf final with the same plate voltage and tube type should work just as well, and be easier to adjust.

Even without a parasitic oscillation problem, some have reported a noticeable improvement in audio quality when the modulator was neutralised. (This could be due to the same placebo effect, the kind of "noticeable improvement" that has made such a success of audiophoolery.)
 

[WA2ROC]

Autek WM1 manual (PDF)

[KE5YTV]

Thanks Dick, you're the man !   

Mike

[WA2ROC]

Mine didn't come with a manual either.  Google is our friend!

[WD5JKO]

Mine didn't come with a manual either.  Google is our friend!

   I find it odd that the manual document resembles a 1950's EF Johnson manual where the schematic is hand drawn with the aid of a stencil, and typed with a mechanical typewriter, then making copies of copies, and then scanned into a PDF. Don't get me wrong, I think the Autek folks have nice designs, but documentation seems to be an afterthought.

Jim
WD5JKO

[KE5YTV]

My WM1 came without the wallwart. It is the older model without lighted meters. Someone said that it uses a special one with reversed polarity. Can anyone verify this?  

[KF1Z]

Autek WM1 manual (PDF)

Of course that's the pick-up head, and not a schematic for the unit itself.......

I gave up trying to find that.... short of writing to Autek and paying for the priviledge.

[WA2ROC]

Fireball:  Mine has a note on the back stating something to the effect of :  "...the center connection on the power plug is negative and the outer shell is positive..."

Why they did this is a mystery.

If anyone has ideas about illuminating their older WM1 meters, let me know how you do it. 

I'm thinking a pair of wide dispersion LEDs in each meter behind the black front part, but you'd have to drill holes through the meter case to get the wires to the power source.

[W2VW]

Somewhere around here I have a junk one of these if somebody needs parts.

[KE5YTV]

I need the wallwart for the old first series. The plug is the "minature phone plug" type. 9-12v. Looks like I may have to go to the Radio Crack for a universal type.  Autek says they used several different types during production.

[KA2QFX]

A wire wound works fine for an audio parasitic.....aint no RF getting out thru the mod iron.

Must me the nickelchrome.

Dave, you kill me!

Nickel Chromium for audio too?! Never thought of that. I have a whole bunch left over from Brent's amp. What do you think the audiophools will pay for two turns of that on 5 watt resistor? LOL!!!

Voo-Doo science indeed. I have to go break in power cord now.