>On the parasitic suppression front, I have some very good data plotted now
>that show conclusively the effects of several suppressors on a 40 Mhz plate
>strap/cap parallel resonance, that is very strong. Other resonances are not
>so important to me right now, as they are things like the pi network
>inductor, and the output capacitance resonating with something or another.
>The 40 Mhz mode is so big that it will show up in the plot of the entire
>input to output response, with the amplifier turned off. The fundamental,
>of course, shows here also. I measured the output to input isolation
>yesterday, using the output connector to drive the amp, and the HP high Z
>probe on the plate, then on the grid. From plate to grid I see about 45 dB
>of cold isolation at operating freq in tune, and about 40 dB at the
>parasite freq...
>
>The gain is expected to be high, calculated to be over 30 dB class A from
>the curves. However, due to things like finite cathode to ground impedance,
>I can assume that it will be lower, so it may require more drive. That's
>OK, we have 1 KW available, and only planned to use about 250 watts for
>starters.
>
>The latest parasitic suppressor is still a big hairpin of copper, with two
>shunt 885AS Cesiwid globars across it,
What is the inductance of the copper hairpin-L? What is the intrinsic L
of the Cesiwid resistors? Thanks.
. If you are interested, in the interest of unpure science, I will make
a Ni-Cr-Fe hairpin L of the same dimensions as the copper one, and send
it to you. Please indicate whether the suppressor L is soldered in or
bolted in so that I can pre-tin it with silver-solder if need be.
Compared to copper, the Ni-Cr-Fe alloy material has about 5.5 times more
ESR at 50MHz.
>and it effects a 30 dB loss to the
>mode without touching the normal op freq. (well, about 0.01 dB affect, and
>this is a 5% duty amplifier). Today, I received samples of a new Fair Rite
>ferrite tile, #42, which is used in Anechroic chambers. It is incredibily
>effective when placed next to the plate strap, knocks the >10 Mhz
>resonances down another 10 dB. It is possible that this stuff may be useful
>for ham amplifiers, but should be used carefully so it doesn't absorb the
>desired RF power. It is heavy, fragile, and slightly magnetic.
The scary part of ferrite vhf attenuators is that they tend to distort
the fundamental waveform at full-throttle.
>
>Once we turn on, will start with the short low Z strap, then if the mode
>kicks up, will install the hairpin. I don't want to put bandaid in without
>finding the wound first.
Prior to Mission 25, NASA did not want to improve the booster O-ring
design because they had not caused a real problem. . . It is my
opinion that, from time to time, some weird things happen in
Parasiteville that cannot be easily explained. Alas, Murphy was right.
>Will keep posting when next step occurs.
thanks, John.
>Amp will
>be installed at the load tomorrow. Have to terminate cables, 15 pin
>control, 2 screens, 2 bias, 2 plates, 2 filaments, etc.
>
>John
>K5PRO
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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