Gary, you may be right regarding my power output measurement, but I thought
I knew how you calculate DC power and AC power of sinusoidial waveforms on
my scope, which, by multiplying with 0.707 you have to reduce first to the
aquivalent of a DC voltage.

What confuses me in your suggestion (printed below) is that even after you
rectify an AC signal and send it through a filter capacitor you STILL
suggest to multiply it times 0.707.
I would have thought that would give you the wrong result??

Where do I go wrong, if at all??

Uwe


in article , JGBOYLES at
wrote on 3/12/04 17:19:

So a 50 resistor serves as my dummy load and a meter connected to
the dummy load indicates around 10 volts RMS. If I did my homework that
would indicate around 2 watt output.

Uwe, The 10 Vrms that your meter indicates may not be accurate at 3.5 or 7
MHZ. It is probably OK at 60 hz. What you can derive from the 10 Vrms is
that
the AC-1 is producing power, just not sure how much.
One thing you might try is a method to remove the frequency dependency of
your measurements. Use a 10:1 voltage divider (10k and a 1.11k). Run this
thru a Germanium or Schottky detector diode and a .01 filter capacitor. You
now have a DC voltage that is proportional to power, and relatively frequency
independent.
To calculate the RMS voltage across the 50 ohm load: Read the DC volts out
of the detector-Vdc. Then Vrms=(Vdc*.707)*10.
Example: You read 2Vdc out of the detector. Vrms=14.14 volts. Power into
the
50 ohm load is then: 14.14^2/50=4 Watts. The diode drop in the dector will
introduce some error at QRP levels, hopefully not too much for what you are
trying to do.
73 Gary N4AST

What confuses me in your suggestion (printed below) is that even after you
rectify an AC signal and send it through a filter capacitor you STILL
suggest to multiply it times 0.707.
I would have thought that would give you the wrong result??

Uwe, Wouldn't be the first time I was wrong.
If you rectify and filter an AC waveform, and the read the DC voltage, this
is Vpeak of the AC. In the example I gave, you read 2 vdc out of the detector
circuit. Multiply this times the X10 divider, and you get 20vdc which is Vpeak
across the 50 ohm load. To get the rms voltage across the load
Vpeak*.707=20*.707=14.14 Vrms. 14.14Vrms across 50 ohms=4 watts.
BTW, the reason I suggested a voltage divider (attenuator) rather than
reading directly with a VOM or scope is to reduce the likelyhood of the scope
probe or meter impedance from detuning the AC-1 causing further errors.
If you are using a scope, measure the Vpeak across the 50 ohm resistor,
multiply by .707 to get Vrms.
73 Gary N4AST

What confuses me in your suggestion (printed below) is that even after you
rectify an AC signal and send it through a filter capacitor you STILL
suggest to multiply it times 0.707.
I would have thought that would give you the wrong result??

Uwe, Wouldn't be the first time I was wrong.
If you rectify and filter an AC waveform, and the read the DC voltage, this
is Vpeak of the AC. In the example I gave, you read 2 vdc out of the detector
circuit. Multiply this times the X10 divider, and you get 20vdc which is Vpeak
across the 50 ohm load. To get the rms voltage across the load
Vpeak*.707=20*.707=14.14 Vrms. 14.14Vrms across 50 ohms=4 watts.
BTW, the reason I suggested a voltage divider (attenuator) rather than
reading directly with a VOM or scope is to reduce the likelyhood of the scope
probe or meter impedance from detuning the AC-1 causing further errors.
If you are using a scope, measure the Vpeak across the 50 ohm resistor,
multiply by .707 to get Vrms.
73 Gary N4AST

With the help of some folks here I did troubleshoot my AC-1 tube transmitter
(using a 6V6) and got it working somehow. Since I passed my code test and
had my first QSO using the transmitter and boy was that exciting.

But questions remain.

I monitor the output signal on my scope and notice that right after key down
the waveform contract just a bit and the tone changes pitch. I guess this is
called chirp. I normally use B+ 200V.
If I increase the voltage lets say to 300V this effect becomes much more
pronounced.
I still use an external bench supply capable of much higher currents and I
don't think it is a power supply weakness. In fact putting a VOM on the
supply line shows no sag in my supply voltage.

How can I minimize this and especially keep it from becoming more severe at
higher outputs.


Also, the circuit diagram for the tranmitter did not state the coil diameter
of the pi network. The pi network still has me scratching my head. Coils
with slight variations in diameter give dramatically different results.

Also changing the air cap with one of an identical range can have a vast
effect, which surprised me. Is this the "real world components" versus the
theory???

Uwe

With the help of some folks here I did troubleshoot my AC-1 tube transmitter
(using a 6V6) and got it working somehow. Since I passed my code test and
had my first QSO using the transmitter and boy was that exciting.

But questions remain.

I monitor the output signal on my scope and notice that right after key down
the waveform contract just a bit and the tone changes pitch. I guess this is
called chirp. I normally use B+ 200V.
If I increase the voltage lets say to 300V this effect becomes much more
pronounced.
I still use an external bench supply capable of much higher currents and I
don't think it is a power supply weakness. In fact putting a VOM on the
supply line shows no sag in my supply voltage.

How can I minimize this and especially keep it from becoming more severe at
higher outputs.


Also, the circuit diagram for the tranmitter did not state the coil diameter
of the pi network. The pi network still has me scratching my head. Coils
with slight variations in diameter give dramatically different results.

Also changing the air cap with one of an identical range can have a vast
effect, which surprised me. Is this the "real world components" versus the
theory???

Uwe

I monitor the output signal on my scope and notice that right after key down
the waveform contract just a bit and the tone changes pitch.

Uwe-

I can think of two reasons for the "chirp".

You did not mention your receiver. It is possible that the strong signal from
your nearby transmitter causes the receiver to change pitch.

I assume your transmitter is crystal controlled, since that is similar to the
6V6 homebrew transmitter I started with back in 1955. By increasing voltage,
the crystal current increases. There is an effect due to heating of the
crystal that might cause a chirp.

In the case of my old transmitter, I found that I could get more power output
by changing the 6V6 to a 6L6, which has the same base diagram. However, one
thing that happened along the way was that crystal current increased to the
point that one of my crystals fractured and stopped working.

Looking back, I realize that the increase in power by changing tubes and
increasing voltage, may not have made a significant difference. If you double
your power, the received signal only goes up half an S-Unit. Improving your
antenna can make a bigger difference!

I don't know about the waveform contraction. I doubt it is from overload of
the scope, but it might be due to the tube being a little "soft" due to low
cathode emission in the 6V6.

73, Fred, K4DII

I monitor the output signal on my scope and notice that right after key down
the waveform contract just a bit and the tone changes pitch.

Uwe-

I can think of two reasons for the "chirp".

You did not mention your receiver. It is possible that the strong signal from
your nearby transmitter causes the receiver to change pitch.

I assume your transmitter is crystal controlled, since that is similar to the
6V6 homebrew transmitter I started with back in 1955. By increasing voltage,
the crystal current increases. There is an effect due to heating of the
crystal that might cause a chirp.

In the case of my old transmitter, I found that I could get more power output
by changing the 6V6 to a 6L6, which has the same base diagram. However, one
thing that happened along the way was that crystal current increased to the
point that one of my crystals fractured and stopped working.

Looking back, I realize that the increase in power by changing tubes and
increasing voltage, may not have made a significant difference. If you double
your power, the received signal only goes up half an S-Unit. Improving your
antenna can make a bigger difference!

I don't know about the waveform contraction. I doubt it is from overload of
the scope, but it might be due to the tube being a little "soft" due to low
cathode emission in the 6V6.

73, Fred, K4DII

With the help of some folks here I did troubleshoot my AC-1 tube transmitter
(using a 6V6) and got it working somehow. Since I passed my code test and
had my first QSO using the transmitter and boy was that exciting.


Congratulations! Though it's been many years, I still remember when I made my
first contact with a transmitter very similar to yours. (It was 1954)

As for the chirp, this is partly the nature of single tube transmitters. You
can minimize it with careful power supply design, and just the right amount of
feedback on your oscillator, but a small amount will remain.

The feedback is controlled by the ratio of the capacitors marked C7 and C9 in
the original Ameco schematic. They form a "tap" on the cathode RF choke.
Increasing C7 slightly or decreasing C9 slightly will increase the feedback.
Different crystals will also react differently.

73,

Doug Moore KB9TMY

With the help of some folks here I did troubleshoot my AC-1 tube transmitter
(using a 6V6) and got it working somehow. Since I passed my code test and
had my first QSO using the transmitter and boy was that exciting.


Congratulations! Though it's been many years, I still remember when I made my
first contact with a transmitter very similar to yours. (It was 1954)

As for the chirp, this is partly the nature of single tube transmitters. You
can minimize it with careful power supply design, and just the right amount of
feedback on your oscillator, but a small amount will remain.

The feedback is controlled by the ratio of the capacitors marked C7 and C9 in
the original Ameco schematic. They form a "tap" on the cathode RF choke.
Increasing C7 slightly or decreasing C9 slightly will increase the feedback.
Different crystals will also react differently.

73,

Doug Moore KB9TMY

"Uwe" wrote in message
...

I monitor the output signal on my scope and notice that right after key
down
the waveform contract just a bit and the tone changes pitch. I guess this
is
called chirp. I normally use B+ 200V.
If I increase the voltage lets say to 300V this effect becomes much more
pronounced.
I still use an external bench supply capable of much higher currents and
I
don't think it is a power supply weakness. In fact putting a VOM on the
supply line shows no sag in my supply voltage.

I think 200 V is enough. Someone here probably knows what the AC-1 design
voltage was, but I'm sure it wasn't 300 V, and may be have more like 150 V.
While the 6V6 can handle higher voltages, as a keyed crystal oscillator, you
don't want to overdo it. You could fracture a crystal, too.

There's quite a bit of AC-1 lore online. Use
http://www.google.com/search?q=ameco+ac-1 to find it. I even found a copy of
the original AC-1 manual, but it doesn't show circuit voltages.

Congrats on getting your ticket and making your first QSO. Now it's time to
put this antique away and build some safe, cool, solid-state gear!

73,

"PM"