[Amps] linearity detector and the sonic web page

[nospam4me at juno.com]

Hello again, 

First off, regarding the linearity circuit mentioned below. Yes, 
Collins 30L-1, 30S-1 and a few other  manufactures amplifiers 
include a linearity detector. One very interesting application 
is when the detector circuit is used to actually modify the 
amplifiers bias in operation.  An interesting example of this 
circuit was used in the WRL Galaxy 2000 HF Amplifier. 

You can find the Collins 30S-1, 30L-1 and WRL Galaxy 2000 HF 
Amplifier diagrams on the relocated sonic.ucdavis.edu web page.  
I retired the sonic.ucd server in March of this year and relocated 
the web pages to the radiowrench.com web site. 

I still receive a lot of Email from people searching through 
the amps archives, regarding   previous posts and the old sonic.ucdavis.edu web server site.   Please note the contents 
of the sonic server have simply been relocated to www.radiowrench.com/sonic  

Most all the original sonic server contents plus a few new 
additions are on the www.radiowrench.com/sonic  web page. 

If you'd like to do a quite preview of the mentioned Linearity 
Detector Circuit in the Galaxy 2000 HF Amplifier, the http://www.radiowrench.com/sonic/so02192.html description page 
has a thumbnail picture for a quick preview. If you want the 
full size files, simply download the zip/pdf file from the main page. 

Cheers,
Skipp 
nospam4me at juno.com 
www.radiowrench.com/sonic 

[paste]

> Jason Buchanan wrote:
>
>I noticed in the 1972/1973 ARRL handbooks that I have there is a 
>4-1000A amplifier project with a linearity metering circuit.  Look for 
>the SS-2000 project.  This seems like an incredibly good idea, however 
>I have never seen anything like this in any other amplifier except for 
>something similar apparently in the ACOM 1000A (and presumably the 
>2000).  It seems to me that the ability to tune for optimum linearity 
>would be a "Good Thing"(tm) and the circuit design appeard to be simple 
>to implement.
>
>Was the original designer of this circuit blowing smoke or is this 
>something worthwhile to add to a homebrew amp?

[paste Ian's follow up reply]

I don't have that particular ARRL Handbook, but the circuit is possibly 
something like Collins use(d) as combined tuning/loading/linearity 
meter. It is described in 'Single Sideband Principles & Circuits' by 
Pappenfus and his Collins colleagues.

It's simply a pair of diode detectors. One looks at a sample of the 
cathode  RF voltage (typically at the in a GG amp) and gives a negative 
DC output. The other looks at a sample of the plate RF voltage, and 
gives a positive DC output.

These two outputs are combined through a DC balance pot, and fed to a 
center-zero meter. When the amp is correctly tuned and loaded, this 
internal pot is adjusted so the meter reads exactly zero. For improved 
linearity, you would probably load on the heavy side from the point of 
maximum RF output, in the usual way. Whatever you decide is "correct", 
you set the balance pot to read zero under those conditions.

To use the meter for pi-tank tuning, simply tune for maximum rightward 
(positive) deflection.

As a loading indicator, the meter is actually measuring the *gain* of 
the amplifier - it reads zero when the amp is loaded to give the correct 
level of gain. Too much gain (too light loading) makes the meter move 
right; too little gain (too heavy loading) makes the meter move left.
Any single-meter (or single bargraph) indicator probably has to be of 
this 'Collins' type. To use it, simply tune for max, load for center 
zero, and repeat those two steps until you're exactly there.

With normal modulation, the needle should stay pretty much on zero. If 
the amp is overdriven into flat-topping, the gain will drop and the 
needle will move leftward, so it acts as a simple linearity meter.

It's obviously pretty easy to automate the basic tuneup procedure in a 
computer-controlled amp. More advanced auto-tune amps use a separate 
phase detector to identify the correct output tuning point, which is 
0deg phase shift between input and output (for a GG amp).

Hmm... my amp has an unused position on the meter switch... thanks for 
making me think about this, Jason!
Ian

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