On Sep 25, 2006, at 1:36 AM, pentalab wrote:
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
On Sep 24, 2006, at 5:05 AM, pentalab wrote:
--- In ham_amplifiers@..., R L Measures <r@...>
wrote:
### getter's [per Eimac and Svetlana] are ALWAYS
working... as long as the fil is lit. HV + drive are not
part of the overall gettering process.
Rich- If this is the case, why not use the tubes as they are being
gettered? This has always been the way that I have done it.
### Hey Rich....... if you blow up ur new rebuilt Svetlana
4CX-10,000J... don't come whining to me !
### All I was trying to get at was.... if 16 guys say to
use 48 hrs to getter a new/rebuilt tube.... and anything less is
gonna be a problem... cuz they have tried many diff time
frames... who am I to argue?
Rich - I have run into a number of amateur radio dudes who advise
something that sounds semi-plausible, but instead of being based
in science, it turns out to be an artifice for promoting his guru
status by giving the appearance of having esoteric knowledge.
### Well these dudes were very adamant about the 48 hour
gettering process.
Wannabe gurus and "recognized amplifier experts" feel they have to be very adamant because if one of them admits to even a picovolt of fallibility, he fears that he will lose credibility as a guru with his faithful followers. However, in my view, just the opposite is true. Every human makes mistakes and those who deny they do are their own worst enemy. IOW, if one doesn't know about something, 'tis best to close mouth and open ears.
Example -- When I was planning to build the original "Plywood Box" amplifier two decades ago, I consulted with the greatest amplifier guru in Southern California. When the project was completed and the design errors were fixed, I realized that some of his advice was based on wrong guessing and he would have come out ahead by simply saying "I don't know" when it came to territory he didn't know about.
Forget the science.... real life practical
experience is what counts. The tube is good for 35,000 hrs
b4 a rebuild.....
8171s, and 3-500Zs are more like 20k-hrs IF the fil-V is kept to a minimum.
so what if u leave the filament on for 48
hrs... it can't do any harm.
The point is that the gettering isn't going to happen any better with the HV off as with the HV on. In fact, according to Will's research, up to a point, hotter is definitely better.
A few of these fellows have a
LOT of experience with those tubes....... Jerry at Economy
Electronics buys the entire production run of YC-243's from
Eimac each month [socketless 6000A7]. He told me the same
deal..... 48 hrs.... or u could easily experience trbl.
I know an automobile mechanic who advises changing oil/filter two and a half times as often as Toyota recommends. Who's right?
### Eimac tells me the YC-243's that come in to be rebuilt, none
have had a fried grid in em... that's just a side story.
## I don't have the time or patience to inadvertantly
destroy expensive new/rebuilt tubes.
Rich - I have probably never run filaments for more than a minute
before firing up a new 3-500Z or 8170.
### 3-500Z's need the anodes to show colour to getter em.....
so whether u run the new 3-500Z fil for just a minute or 48
hrs is irelevant.
### How many DOZENS of new 8170's have you fired up ???
the straw man
### You gotta be very carefull here Rich. Anecdotal experience
with just one of anything is no subsitute with experience
with hundreds of the same thing.
I remember the story of Chicken Little.
When a fellow who sells
literally hundreds of big metal triodes/tetrodes.... and has a lot
of experience with em sez 8 hrs is not enough to getter
em.. or XYZ will happen..and does,.... and to use 48 hrs min....
I tend to listen.
I high-pot new or used tubes before plugging one in. If a tube is gassy, I don't plug it in. As I see it, with the exception of tubes with a built in ion-pump, vacuum leakage current Never decreases and it can not be exorcised by an exoteric means.
### when guys tell me 1/2" tubing tank coils run so bloody
hot on 10m, they require 100-200 cfm....
Water-cooled Cu tubing tank coils and water-cooled vacuum capacitors are common in larger commercial amplifiers.
I tend to listen,,,and
not try an re-invent the wheel. [on 10m, you can easily be
dissipating 200w of heat... all of it into just a 2-3 turn
coil.... as opposed to 120 watts of heat on 20m..... and way
more turns on 20m to boot]. Actually 3/4" is better.... and
strap... laid flat... like a parasitic suppressor wound on a
globar is the best for a 10m tank coil.
Strap will have RF
flowing down both sides.... where as tubing only conducts on the
outside. 1.5" wide strap works superb... eq to 1"
tubing... and minimal stray C between turns.
Good points, Jim, but there's a bit more to it. Round tubing has uniform RF current distribution, while strap concentrates RF current at the edges. Thus, at the same current, tubing with the same surface area as strap will show less heating than the strap. For example, Cardwell rates 0.5" tubing at 40A while 0.5" strap is rated at 15A. However, there is a considerable space saving with strap, and it's easier to wind, so I prefer strap.
Jim VE7RF
Yahoo! Groups Links
R L MEASURES, AG6K. 805-386-3734
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