>Rich raises some interesting points. I guess one question to ask is:
>"Are we designing a commercially viable, going to make lots of, device
>OR are we building one offs as amateurs?"
>
... commercially viable, Peter.
>The answer to this has potential for running us down one of two routes.
>Looking at Rich's points:
>
>>IMO, it would be feasable to produce an amplifier that had:
>>1. 2mS - 3mS switching.
>>2. Rheostat-adjustable filament-potential.
>>3. Filament voltmeter function on the multi-meter.
>>4. Low VHF-Rp parasitic suppresson.
>>5. Step-start.
>>6. Tank circuit with appropriate RF current rated components.
>>7. Good input swr with any transceiver.
>>8. Glitch protection.
>
>#1. 2mS - 3mS switching.
>
>Some of the smaller vacuum relays are quite OK at 1Kw plus - carrying,
>NOT hot switching. However, they are abt $75 in the US. ...snip...
At Fair Radio Sales, the price is about $35 for a RJ-1A. At 50 ohms, a
paralled-pair of these guys will handle 11kW of RTTY at 29MHz.
......
>Question: has anyone been really successful with PIN diodes?
Yes. However, there are reportedly failures associated with SWR, and
with lightning discharges within the near-field of the antenna.
>I've got 10 off 1000volt 2 microsecond PIN diodes on insulated stud
>mounts, rated a 1A DC, and 10 of the same wire ended. One day, I'll see
>what can be done. Interesting that W2VJN's company is avoiding PINs
>because George is dubious about the reliability under amateur
>conditions.
George seems to be right, Peter. With 1500w into 50 ohms, one must be
prepared to deal with c. 776 peak-to-peak volts - - which is no problem
for a 1000v PIN diode. Add a bit of SWR, and there just might be a
problem. PIN diodes are more unforgiving than vacuum relays.
>
...snip...
>#3. Filament voltmeter function on the multi-meter.
>
>Amen to that. It's not a difficult or costly thing to do, either.
>
However, one would need a special scale on the multimeter for reading
filament volts, but it would only need to be calibrated over the plus and
minus 5% range of recommended filament voltage. / / For heater-type
bottles, a 723-based undervoltage cutoff protection circuit would be
good.
>#4. Low VHF-Rp parasitic suppresson.
>
>I guess we all have our own opinions on this, and its implentation, but
>the basic principle (as I understand it, the parasitic suppressor should
>have a low Q at VHF) is agreed.
>
- VHF-Q is one way to look at it, Peter. A bit more obvious way to look
at it involves VHF-Rp. For example: In N7WS' measurements with a
Hewlett-Packard Model 4191A RF Impedance Analyzer, at 100MHz, a
conventional suppressor made from copper-wire had a Q of 2.2, and a
similar suppressor made from resistance-wire had a Q of 1.5. This isn't
much difference. However, the copper-wire suppressor had an Rp of 166
ohms, and the resistance-wire suppressor had an Rp of 101 ohms.
The objective of VHF suppression is to reduce VHF voltage gain. Since
such gain is basically VHF-Rp*Mu, lowering VHF Rp is our goal. This
concept is nothing new. F. E. Handy recommended using the technique in
the 1926 and 1927 Editions of the Handbook.
I find it a bit curious that Mr. Rauch has stonewalled the subject of F.
E. Handy's pioneering observations on VHF parasitic-oscillations back in
the 1920s.
>#5. Step-start.
>
>An alternative that can be very cheap after a good flea market, is a
>motor (or even hand?) driven Variac. Otherwise, I would say that step
>start is a sine quae non. For production, it isn't that expensive,
>either.
True, but a pair of 7w resistors and a dpdt relay are faster, cheaper,
lighter, and won't trash the high voltage regulation.
>
>#6. Tank circuit with appropriate RF current rated components.
>
>This surely comes down to deciding what the application is.
...snip...
>
>#7. Good input swr with any transceiver.
>
>I must admit I don't understand this. If the input SWR is good
>(<1.5:1?), then why should the driving transceiver come into it?
Because some transceivers begin to throttle down when the SWR is above
1.15.
.....
>#8. Glitch protection.
>
>I assume that by this, Rich means the 'spike' of energy of much higher
>level that the transceiver can produce before its own ALC grabs the
>output.
No. ...... During the Grate Parasitics Debate, in an attempt to explain
mysterious tank arcing, numerous naysayers claimed that humungous amounts
of overshoot peak-power could be produced by garden variety transceivers.
I have measured some radios that had as much as 60% overshoot, but
nothing like what was claimed by the naysayers -- who claimed that
ALC-related overshoot could not only cause tank arcing, but also cause
(grid) gold-sputtering, grid/filament shorts, burn out parasitic
suppressor resistors, et cetera. IMO, such claims were not supported by
the evidence - - i.e., the naysayers were seemingly headed down that wide
river in Egypt.
. .... .. ....
>One thing about old fashioned tube PA's in transceivers - that's a
>problem they didn't tend to have.
>
A TS-830S produces about 100w key-down and 145w on voice peaks.
...snip ...
>But I believe that many modern transceivers can heavily overdrive modern
>grounded grid tubes anyway.
Every tube, whether it be a g-g type or a grid-driven type, has finite
cathode emission. For instance, a pair of 3-500Zs, with 3kV on the
anodes, will deliver about 1500w with 120w of drive. However, when
driven with 240w, they will not produce anything even close to twice the
output. The reason is that cathodes have finite emission.
- Another angle: If ALC-overshoot were really responsible for tank
arcing, the tank would pretty much arc at the beginning of each spoken
sentence, however, this not the case. Tank arcing may not occur even
twice on the same day of operating. In my SB-220, tank arcing was seldom
observed. After I lowered the VHF-Q/Rp of the VHF suppressors, tank
arcing has not been observed by this operator.
... ... ....
Rich---
R. L. Measures, 805-386-3734, AG6K
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