That's fascinating information, Dave. Thanks for that. I always wondered how
this was done. Big lads' toys.
As for "a responsible amplifier design is one that won't get damaged when an
arc occurs" well my solution is low-tech: an HRC fuse (I bought a sackful from
the army suplus store) and a BIG glitch resistor. Also glitch diodes on meters
etc. I hold the negative HT quite close to earth so there won't be anything
too horrid happen to B- if there's a fault.
So far, I've managed to kill neither an amp nor myself. My wife has given me
strict instructions not to electrocute myself.......
How do other people in the group create flashover protection? I seem to
remember a very clever OE5JFL circuit in Dubus some years ago
cheers
Dave G0OIL / K2MOO
--- On Wed, 28/1/09, Dave Haupt <w8nf@yahoo.com> wrote:
From: Dave Haupt <w8nf@yahoo.com>
Subject: [Amps] De-gassing/de-barnacling YC-156 tubes (was Source for YC-156
tubes)
To: amps@contesting.com
Date: Wednesday, 28 January, 2009, 10:31 PM
I visited the Eimac factory in San Carlos circa 1989-1990 for the purpose of
witnessing the manufacture of the YC-156 tubes, which my employer was using in
production at that time. If your YC-156 has PEM nuts in the grid ring, it was
built for us.
IIRC, Eimac's procedure for final de-gas and de-barnacling the tube was to
immerse it in oil (so it would not arc externally) and run the cathode/anode
potential up to 20kV with a current-limiting resistor and an energy storage
capacitor. They ran them this way for some number of days, with no heater
power.
At the factory, our procedure was to run them in the amp, with heater and HV
applied, for 72 hours. They'd arc a half dozen times the first day, then
settle down. Our HVPS had a very fast shut-down but no crowbar.
Were I to do it in the home shack, I'd string up enough resistors to get a
few Megohms at 100 watts, feed them into a few uF worth of capacitance at high
enough voltage, and run the whole thing at about 15kV. The Joule storage
capacity of the caps would ensure that enough energy is transferred during an
"event" to adsorb the gas into the copper anode (the heated copper
anode is the getter in the YC-156: no amount of heater operation will getter the
tube), or melt off the barnacle, whichever condition causes the arc. In a used
YC-156, it's more likely gas; what we witnessed in young tubes was proposed
by Eimac to be the barnacle issue (aka Rocky Point Effect).
Also, bear in mind that it is not possible to guarantee that a tube won't
arc, so a responsible amplifier design is one that won't get damaged when an
arc occurs.
73,
Dave W8NF
K7RDX wrote:
>> I have purchased several YC-156A pulls from this vendor and nearly
every one
>> tested very good. They will exchange if you get a bad tube,however I
suggest
>> if building from scratch to have your tubes tested..Will save hours of
frustration when you finially light off the new amp..Remember: Most of the
pulls offered have been stored for several months (Or years) so de-gassing
is a good idea before use. I test my tubes filament for rated current
pull,hi-pot for twice rated dc voltage,and run in a cooled jig with filament
>> voltage for at least 8 hrs and then hi-pot again before testing with
hv in
>> my amp.It`s a lot of extra work but saves other component failure in
the
event of a flash-over..Zonum Industries will do this procedure for around
100 bucks plus shipping. GL,Jim..K7RDX..
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