>> 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?
Haven't measured it. I probably could, but it's a good question.
>
>> 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.
>
Definitely good suggestions. I'll think about it. For number one what
value cap would one add in series? I haven't seen that before.
>> 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?
Well, it would be difficult for my bandswitch to fail as it is a big B&W
coil/bandswitch unit. And no, no other stuff. I did have a weird thing
happen that blew out some resistors a couple of weeks ago. But it turns
out that the tube was bad. IMHO, it had to have been an oscillation with
"unseen" stuff, but again, it was a bad tube.
No, none of the strange stuff happened. Just an increase in plate and
grid current as I tweaked the caps with no input signal......
>
>> 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.
>
Yes, it's true. I am going to try a couple of other things this
afternoon.
>> 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?
It's a standard 4 section cap. No idea of it's value though since I
didn't build the amp originally. It seems to like to operate near the
meshed position a lot of the time. Maybe I am not tuning the amp up
correctly. 15 meters has a false tune point when the cap is meshed but
tunes up better when you decrease the capacitance about half way. Maybe
I am doing the same thing on 10. It's a 80 thru 10 amp, BTW.
73,
Jon
KE9NA
-------------------------------------
Jon Ogden
KE9NA
http://www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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