[AMPS] Amplifier Experiments!

[Tom Rauch]

> Date:          Sun, 24 May 1998 10:31:03 -0500
> From:          Jon Ogden <jono@webspun.com>
> Subject:       [AMPS] Amplifier Experiments!
> To:            amps@contesting.com

> First I put in my original supressor design.  This consisted of 3 3watt 
> metal film resistors in parallel with about 70 Ohms or so total 
> resistance.

What is the inductance of the resistors? Can you measure it?

> nH inductance.  I had earlier tried more than one turn, but the resistors 
> kept burning up.  

Alternative solutions:

1.) You could have added capacitance in series with the resistors to 
reduce 10 meter current, while using the large suppressor inductor. 
In the AL-1200 amplifier, an intentionally inductive resistor is 
series resonated at 100 MHz, the frequency where the tube likes to 
oscillate. This series resonant suppressor is then placed 
across the standard inductor.

2.) The inductor could use less turns, and be PARALLEL resonated at 
80 MHz.  Then the resistors (assuming they have zero reactance would 
series load the anode with their entire resistance. This solution is 
offered in some 4-1000 articles.

> Anyhow, on 10 meters, I was able to get out about 1200 watts with about 
> 95 watts in.
> 
> Then I decided to key the amp but provide no input signal.  I then varied 
> the tune and load controls to see if I could make the amp oscillate.  As 
> I decreased tune C down close to its minimum value, plate and grid 
> current took off.  I had made an oscillator!  So obviously my supressor 
> design did not work!

No band switch failure? No bent filaments or blown grids? No HV 
arcs or exploding chokes or meters? What happen to the catastropic 
explosions due to an oscillation we can't even see?

> Next I took replaced my supressor design with supressors I had built from 
> an AG6K kit.  Put them in.  Power out was not about 1050 Watts.  So I did 
> have about 150 watts of loss in the supressors.  And I am using 3 runs of 
> nichrome wire after the supressors to the blocking caps.  Anyhow, the GDO 
> dipped at 80 MHz, but much, much less dip.  I put the dip coil in 
> *exactly* the same place as previously.  Then I did the same zero signal 
> experiment.  No oscillations occured regardless of the tune and load C 
> combinations.  The amp was completely stable.

Another way to skin a cat, but with addition loss at the desired 
frequency.
 
> So Rich's supressors work far better then mine.  Am I concerned about 150 
> Watts?  Well, it's less than 1.5 dB so  probably not.  And actually I 
> think I can get more power out on 10 m if I could get a little more load 
> C.  It's fully meshed when I tune up and pretty much stays that way.

What king of load cap do you use that is fully meshed on ten meters, 
or is the amp a "ten meter only" amp?


73, Tom W8JI
w8ji.tom@MCIONE.com

--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm