[Amps] De-gassing/de-barnacling YC-156 tubes (was Source for YC-156 tubes)

[Dave Haupt]

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..