Amplifier linearity

[W9BHI]

Some manufacturer made a linear amplifier that had a center reading meter that assisted in tuning for best linearity.
Does anyone remember who the manufacturer was?

Thanks,
Don

[K1JJ]

Some manufacturer made a linear amplifier that had a center reading meter that assisted in tuning for best linearity.
Does anyone remember who the manufacturer was?

Thanks,
Don

Hi Don,

Back in the 90's I had a schematic of a 4CX-10,000 (driven by a 4CX-1000?) linear amplifier that used a signal sample from the input and output and passively compared phase. It used toroids to do it. It mixed them together and used a center reading meter to evaluate. (Zero phase difference = best linearity)  It used a few diodes in the circuit too.  I cannot seem to find it. But it was from a commercial amplifier like TMC or somebody of that vintage and construction technique.

Evidently it worked well for the purpose.

Tom, K1JJ

[W9BHI]

Tom,
That is what I saw on an amplifier schematic once long ago.
I just don't remember what it was.
It compared the input to the output and when the meter was centered it was tuned properly.
Don

[K1JJ]

Don,

I'll bet you could reverse engineer it on a breadboard.

Use a small toroid at the input to sample some RF. Do the same at the output.   Be sure to have a zero degree phase relationship, like one grid driven tube driving another, input to output = normally zero degrees when tuned properly.   (Or flip the phase winding of one toroid sampler)


Rectify the outputs with diodes and mix. There was some kind of center tap relationship to normalize the two amplitudes IIRC.  The result should be zero DC output to the meter when the phase comparison = zero degrees.

However, I'll bet that schematic is around. I searched on Google for schematic images, but saw nothing after a short time. A guy on the web sent it to me years ago when I was considering negative feedback for a series of grid-driven RF stages.

T

[n2bc]

The Collins 30S-1 and the 30L-1 each had a linearity circuit which could be monitored on the multimeter.   

[W9BHI]

N2BC,
That is a clever circuit designed to show when the loading is set to match the plate impedance of the final tube.
The same thing that Acom is using in their 1000 amplifier.
They call it plate load "true resistance indicator".
Very fast band change and tune up.
I used to own one, great little amp.
I would like to be able to adapt that circuit to a pair of 4-400a's in class C plate modulated.
Knowing what the plate impedance is for two tubes in parallel would be a start.
Thanks,
Don

[W1ITT]

WD7S has a linearity monitor on the Triode Control Boards that he sells.  There's a description of it in the "manual" pdf on his page, but basically it looks at the ratio of input rf voltage to output rf voltage and displays it on the bar graph display that he also sells.  It requires an initial setup where the user tunes up for "best linearity", presumably with a two-tone test and spectrum analyzer.  After that, as long as the gain at any given drive level is proportionate, it keeps the LEDs in the green.  If the ratio of output to input drops off, the assumption is that the amplifier has been driven into nonlinearity and the display will so indicate.
His boards are well made and user friendly.

[Opcom]

like this maybe? I'm digging up the theory on it. It's from the GRC-106

[Opcom]

A zero center meter is used. Because it has a phase discriminator it might be useful for the topic purpose.

[N8ETQ]

      IIRC some of the auto-tune Military
rigs used a similar scheme. The GRC19 (T-195)
did for sure.


      Apparently it compared the input phase
to the output phase hence the discriminator.


/Dan