[Amps] 10 kw CCS on 6M

Tue Sep 13 01:13:53 EDT 2022

Having worked with really big transmitters; Telefunken 100 kW ISB and Thomson-CSF 500 kW carrier AM,
tune-up works in very similar ways for all practical purposes.

First the low-power drive stages are peaked up for maximum drive voltage to the penultimate
driver grid. After this, the procedures differ somewhat between linear amplifiers for ISB and AM transmitters that are
Class C in the drivers and PA stages.

A servo-tuned ISB transmitter uses the phase relations between the grid and plate circuits to establish resonance,
and then is the plate circuits and their coupling circuits adjusted to present the proper load-lines to the tubes. 
Finally, the drive level is adjusted so the proper output power and linearity is reached. 

In order for this to work properly, the tuned circuits need to be pre-set quite closely to their final positions. 
This was mostly accomplished by measuring the input frequency and use this information to access tables of stored
tuning information, either established after the last successful tuning operation, or at the design stage of the amplifier.

"Before computers" this was done by dividing the tuning range of the amplifier into many sub-ranges and then use the measured frequency for choosing one of the ranges with its preset information. After this, "Auto-tune" mechanisms with servo motors were first brought to their initial positions, and after this phase and load-line discriminators took over control.

Class-C transmitters used grid and plate currents to establish resonance conditions, and were tuned progressively from the drivers to the final stages at reduced power. As the final step, the drive was increased to reach the proper carrier output level before high-level modulation could be applied. 

The Thomson-CSF transmitters did not servo-tune in the proper sense of the word, but used stored settings for each frequency. Instead, the servo-motors brought the tuning elements to their pre-set positions without any room for adjustments.  This worked well because the tuning settings become quite broad when operating into a broad-band antenna, and there are no critical linearity specifications for a Class-C AM transmitter.

73/
Karl-Arne
SM0AOM

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Från : amps at contesting.com
Datum : 2022-09-13 - 00:06 ()
Till : amps at contesting.com
Ämne : Re: [Amps] 10 kw CCS on 6M

 One of the things I see that is different, as I have watched videos of the bigger transmitters firing up, is that they can bring the driver stages online, and have them drawing plate current, tune them, and then engage the final. Obviously, there is not tx/rx relay for a plain transmitter. So, where does that drive power go while the driver(s) are being tuned, and the final is on standby? There are plenty of such videos out there that are exciting to watch!

FM of course, does not have any 'swing", so you crank the carrier where you want it to be, and it just sits there. AM on other hand of course, is set for about 25% of max carrier, and them modulation takes it up and down from there. Based upon that description, when WLW was running a full 500KW, I'd assume the engineer would set the carrier around 125KW, and then 100% modulation would peak at 500KW. 

Any way you slice it, that is a bunch of RF up the feedline!

Don N8ECH

In our case, we engage the tx as a unit, and then tune for appropriate readings, and/or maximum smoke, lol.
     On Monday, September 12, 2022, 03:19:34 PM EDT, Peter Voelpel <dj7ww at t-online.de> wrote:  

 Yes, no difference, just bigger and more powerful.

73
Peter, DJ7WW

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Kim Elmore
Sent: Sonntag, 11. September 2022 03:36

Don Fox raises a question I've wondered about for years: how are these very
high power amplifiers initially placed in service? Today, we have VNAs we
can put in the palm of our hand, how is it done now and how was it done when
there was nothing but vacuum tubes? How adjustable are the PA output
circuits? It can't possibly be done the way we tune our puny 1.5 kW amps. 

Kim N5OP

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