I have used a scope to monitor filament voltage on a large number of
commercial amps and have yet to see one where the filament transformer or
winding does not do an excellent job of limiting inrush.
If the HV hasnt been recapped with over 25-30 uF total that transformer or
winding is also a good inrush limiter also offering switch protection..
If spending money is of no concern then by all means buy whatever keeps you
happy amd hope you do a very good job installing it..
Any old tube, today or in the future should be brought up on a Variac to be
sure it hasnt gone partially to air which will not show up initially on a
glass envelope. NOS US built 3-500Z's are already becoming scarce as are
4-400A's which can often be easily adapted. The 4-250A can be used at
reduced power at the same voltages as the only difference is the anode
construction; the PL-175A also shows up at times as well as various 4 digit
numbers for the others.
IF OK then bring the filament, plus HV up slowly to about 1200V and look for
the telltale glow of outgassing. Do notkey the amp and never with RF at this
stage. With amps using the old CW/SSB switch about 1800-2000V in the CW
position is the norm and if the gas is not excessive it will not cause an
internal arc.
In all amps I highly suggest a HV surge, aka glitch, resistor sizeed to
limit fault current to a safe level and allowing fuses or breakers to blow.
A 25 Ohm 50W Vitreous Enamel resistor is the ONLY choice I suggest (25W on
SB-200, AL80's power level is fine) as it will absorb the high current
without self destructing as does sand type or other cheap substitutes.
Ceramic/metal tubes are not immune to outgassing but that is limited to a
small variety...at least this year. Id be worried about Russian and Chinese
offerings. Philips and other mainline EU tubes seem excellent IMO but I
havent tested enough types to be 100% sure.
There are several ways to regetter a tube which is a different subject I
have detailed many times over many decades..Perhaps someone has preserved a
file.
Carl
KM1H
Amp service since 1964
----- Original Message -----
From: "Leigh Turner" <invertech@frontierisp.net.au>
To: "'Rob Atkinson'" <ranchorobbo@gmail.com>
Cc: "'AMPS'" <amps@contesting.com>
Sent: Tuesday, December 26, 2017 5:27 PM
Subject: Re: [Amps] Life of tubes in ham service
Rob, I concur with your succinct sentiments here about transmitting tubes.
The only proviso I would make is the inclusion of a soft-start mechanism
on
the filaments to bring them up slowly in a controlled manner at initial
switch-on; and ensure the filament voltage as measured at the socket pins
is
tightly within manufacturer's specification.
73
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Rob Atkinson
Sent: Wednesday, 27 December 2017 3:45 AM
To: amps@contesting.com
Subject: Re: [Amps] NXP 65V LDMOS 1K80H-1800W
"What happens when they quit making tubes?"
For some tube types that happened decades ago. But you can still find
plenty of good 810s etc. decades later.
In other words, what happens when no tube of any type is made?
Answer: Not much, except prices may go up.
What happens when tubes no longer exist?
Not our problem because we'll all be SK.
Why are you so flippant?
Because millions of tubes have been made and for ham use, a pair of
3-500Zs (to use them as an example), will outlast all of us _if they
are treated properly_.
That's the rub. Broadcasters wear out tubes because they run them day
and night non-stop for a year or two and they lose emission.
Hams don't do that. The only time a tube wears out in a ham rig is
when hambone abuses it, usually by running too much plate current or
grid current.
Most common is the single 3-500 "Kilowatt amp" that pisses away 3-500s
every 3 years or so. A certain manufacturer should get a medal from
the Chinese company making 3-500s these days.
If you know how to run your tubes, they'll be running after you are in
the ground.
73
Rob
K5UJ
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