>short for time I over simplify.
>>
>>First of all I have no particular disagreement with the use of a
>somewhat
>>lossy material in the suppressor.
>
>At least, not since N7WS published his vhf suppressor measurements.
Actually I never heard of his measurements until you showed up on the
reflector. My use predates yours by probably 30 years.
BTW, how come Wes disavows all of your claims in his name????
>
>>I have commented since the beginning of
>>this reflector that National Radio went that route in a military
>tetrode
>>amp back in the 60's. I use that same strap today in my
>work.....bought a
>>roll of it at the final National IRS auction several years ago. The
>main
>>difference is that Rich tries to get by with #16
>
>#18 Ni-Cr-Fe alloy
Even worse IMO but that is nit picking...your speciality.
>
>>wire whereas National
>>used 1/2" wide strap around a big 50 Ohm non-inductive resistor.
>
>There is no such thing as a non-inductive resistor. A big globar type
>
>resistor has over 100nH, which is roughly the same L as a typical
>suppressor inductor has.
Give it a rest Rich.. Give part numbers and real measured values, not the
usual generalities. With real numbers we may be able to confirm your
values.
>
>>I do object to using that material in the complete plate to blocking
>cap
>>path and prefer the traditional low inductance wide silver plated
>>strap/tubing strap.
>
>The two, parallel resistance-wire arrangement we use has about the
>same
>inductance as a silver-plated strap of the same width, which is why
>the
>anode-resonace changes little after the resistance wires are
>installed.
>Sure, in medium size amplifiers it gets pretty warm at 28MHz due to
>its
>inherently high VHF-ESR.
Sorry but two #18 wires do not equal a 1/2" strap for inductance...not
even close. You may continue to fool some but you are beginning to remind
me of Rauch when it comes to generalizations, magic numbers and drifting
off the subject. Are you guys related?
. For tetrodes with handles size
>amplifiers,
>we supply nichrome-80, 0.25" ribbon.
>
>>If the suppressor is doing its proper job right at
>>the tube then there is no reason to continue nichrome to the blocking
>>cap.
>
>Every VHF ESR-ohm in the anode resonant circuit contributes to
>Decreasing
>the VHF parallel-equivalent resistance (Rp) load presented to the
>anode,
>which decreases the VHF amplification of the tube.
And every Ohm equals more loss and more silver solder. It would seem to
make more sense to cure the problem instead of modifying the symptom.
.
>
>>Layout is critical and in a sloppy version it may be necessary to use
>>more nichrome or whatever. But in a good layout I would think that
>the
>>lowest possible inductance in order to move resonance above the tubes
>>ability to oscillate would be the "good engineering" approach.
>>
>Indeed. The Tune C should be close to the anode. To minimize L,
>vacuum
>capacitors should be mounted vertically , as Jennings recommends, and
>driven through a Multronics right angle drive under the chassis.
Pretty hard to do in a SB-220 or other commercial amp. A bit overkill in
any ham amp under 3000W or so.
>
>>Secondly, I have harped for a year about VHF resonances in the tank
>>circuit with nary a bit of comment from anyone. Now I see that Rich
>has
>>finally added that possibility to his ever varying repertoire.
>
>As I recall: I discussed this with Mr. Rauch during the grate
>parasitics debate, and we semi-agreed that a typical HF tank inductor
>acted pretty much like an RF choke from 90-150MHz. The major VHF
>resonances are in the Tune capacitor.
That debate was not on this reflector and I have no idea what transpired
elsewhere. As far as major resonances....depending upon the actual switch
and mounting method there are also resonances between various switch
components and the hardware. Two silver plated wipers seperated by a
piece of ceramic also make a damn good capacitor.
>
>>National Radio solved that problem very neatly in the NCL-2000 and
>NCX-1000 by
>>adding a SERIES cap...not a shunt as has been discussed about here
>the
>>past few days. The National engineers added a 10pf capacitor across
>the
>>20 and 40M shorting bandswitch contacts which eliminated a
>particularly
>>nasty proclivity to arcing.; perhaps you would wish to analyze that
>>circuit.
>
>It would be better than using no 10pF capacitor, however, there would
>seemingly be less stray inductance if the capacitor made a less
>circuitous path to gnd.
It is my understanding that the ground path was not the issue, rather a
low Z path around the tank L and directlly to the load. Perhaps someone
would care to really analyze tht circuit.
>..........
>>Thirdly, my dis-belief centers around the big bang and that is where
>I
>>suggested ( or that was my intent anyway) an article. You are the
>>engineer, show me how a VHF parasitic has enough energy to bend a
>3-500Z
>>filament.
>
>The parasitic apparently produces a surge in DC grid current because
>an
>underloaded high Mu triode oscillator exhibits large grid current.
>In a
>TL-922, the grid current surge is large enough to burn out the 1A RFC
>from the grid to gnd. Since all grid current comes from the
>thoriated
>tungsten filament, and all electric currents produce mechanical force,
>
>why couldn't enough current produce sufficient force to bend the hot
>(1820 deg. K) filament helices?
Explain the mechanical force necessary to bend the filament. Then
translate that to electrical energy. Then show where that energy comes
from in an amp with a current limited filament xfmr???
How does one know that a parasite
>took
>place during the big bang/shorted 3-500Z filament/grid? For starters,
>I
>would measure the resistance of the VHF suppressor resistors and
>inspect
>their appearance.
About as useful as checking ur undies for hash marks...a visual or smell
test usually works.
In an amp that is completely stable when keyed...no drive...at or close
to its dissapation rating AND varying Tune and Load C while keying the
relay line...there IS NO WAY that it can then magically go bang when
biased well into standby. I dont care how many Web pages you use or
sacrificial virgins...it just cant happen from a parasitic.
>
>>I say it is a gas/plasma discharge
>
>However, in a G-G amplifier a plasma discharge would be from anode to
>grounded grid. Such an arc would not reach the filament.
Why not? What happens when the anode is at the B- rail at the critical
instant of the PS discharge? Is it that hard to visualize the filament to
grid path then? The initial BANG is not the plasma anyway...that occurs
at some finite time later and is a creation of the arc.
In the
>dozen
>or so kaput 3-500Zs, with bent filament-helices, I have autopsied, I
>have
>not found one with an arc mark on the grid cage.
So how do you then explain a filament to grid short with a bent filament
if there is no contact path? Magic again? Or do they just do their
damage and leave no visible trace?
{see page 15 of 9/90
>
>*QST*}
>
>>and partially caused by barnacling
>
>It is my opinion that if there were "barnacles" that produced internal
>
>arcs, one would undoubtedly find arc-marks when one finds bent
>filament
>helices. . So far, the barnacles theorm is not supported by
>evidence
>-- i.e., "barnacles" may be a 'sea-story'/ 'junk-science'.
Beats me...I would prefer to believe Eimac, other tube mfgs and countless
users. If you can prove your version of reality then by all means go for
it. Just let us all know where and when it will be published.
>>
>>.........
>>And finally....No, I have not built a ton of amps but there are
>certainly
>>plenty of established companies that have. I would prefer to give
>their
>>engineers the credit they deserve and cite the megatons of stable
>amps
>>that they have shipped to military and other customers. A few persons
>act
>>as if they are the sole sources of these revolutionary "new ideas"
>but in
>>reality there is absolutely nothing new at all.
>
>Agreed. F.E. Handy wrote about it in 1926. Another chap apparently
>wrote about in 1935, I think in the IRE journal.
>>.........
>>My own suggestions for an amp would include:
>>
>>1. HV surge suppressor resistor of a value and wattage that can limit
>the
>>instantaneous PS discharge current to a safe non-destructive value.
>
>agreed
>
>>2. Use of a suitably placed series capacitor in the tank circuit to
>>provide a low impedence VHF path to the load.
>
>What kind of a VHF load is a 20m yagi?
As good a load as a 50 Ohm Bird or did you forget the loss of 100' of
RG-213 at 150-200 MHz? Coax makes a damn good load at VHF and above.
Granted this will not work with the guy using 1 5/8" hardline to his 20M
yagi.
It seemingly makes more sense
>to
>put 10pF from the output end of the Rs/Ls vhf suppressor to chassis
>gnd.
Yep and then forget about 10M operation...plus the expense of a 10pf HV
cap that will actually work at VHF.
>
>>3. Use of a suitably sized parasitic suppressor resistor and phase
>out
>>carbon composition. A 5W metal oxide should be the minimum for
>3-500Z
>>size tubes; a pair of them for the 4-1000A.
>
>>4. Use of a resistive suppressor L material only if necessary to tame
>a
>>known problem tube such as the 3CX1200A7 or to compensate for layout
>>problems.
>
>Why wait for trouble to come knocking?
Good idea for sloppy design....go for it.
73 Carl KM1H
>
>- later, Carl.
>
>cheers
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K
>
>
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>
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