Dick and others...I forgot to mention cooking in the 8122's since they
have sat for 20 years.
There are probably several versions for the procedure but this is what I
have used successfully with indirectly heated tubes: (after the DC path
is known to be OK).
Run filaments and air only for 24hrs, disconnect the HV.
Then preset the bias pot on the NCL-2000 to the highest negative voltage
which is usually about -45V.
Key the relay in the CW position with no RF drive, there should be only a
very small, if any plate current reading. Slowly reduce the bias voltage
until you get about 50ma of plate current. Also monitor screen current
with the other meter....there should be no indication. Let this run for a
few hours and stay close to the AC breaker! The NCL has HV and Screen
current limiting resistors for catastrophic arcs but you still want to
keep an eye on the meters.
The next step is to run the idling current at 100ma in the CW position
for a few more hours.
If all is well, crank the CW idling current down to almost zero. Unkey,
switch to SSB and key up again. Bring the idling current slowly up to
200-250ma and let this run for 4 hours with the same precautions as
above. This is usually the time you will have a gas arc or a screen will
short if the tube has been previously abused. Gas will usually show as a
slightly negative screen current. Screen emission will be slightly
positive.
You will now be dissapating up to 650W or so with both tubes which is
well within ratings but will probably curl the paint on the cabinet!
I usually defeat both interlocks and have the cabinet removed during all
testing. DO NOT try this unless you are 110% confident and understand the
risk. That was the way we did it at National before OSHA and other
busybodies came along and we never lost a tech. The bleeding hearts today
would probably stain their undies if they ever saw the way things were
done then, even in the military division. Yet I know of no
case....ever....where anyone there was injured, zapped, killed, etc by
high voltage.
BTW if you run the amp horizontally with the cabinet removed prop it up
on a few 2x4's...the air intake is from the bottom.
GL Carl KM1H
SNIP
>8122's are still in production by Burle who bought the old RCA line.
>Others are Eimac 8122W's and Amperex. The Mil-Spec Eimacs are bullet
>proof....I have a pair here I use when converting the NCL to 6M and
>they have survived all the abuse I can give them while taming
>parasitics.
>
>I have all field bulletins, etc and may be able to help you with
>problems...BTW, I would need the serial # off the back panel which is
>stamped in black ink.
>
>73 Carl KM1H
>Amplifier Repair and 6M Conversions Our Specialty
>National Radio 1963-69 and part of the NCL-2000 design team
>
>
>
>On Fri, 11 Sep 1998 09:48:45 -0500 Richard Carroll
><w0ex@scan.missouri.org> writes:
>>
>>I have just acquired a very nice old
>>National NCL2000 amp (along
>>with the matching NCX5 transciever &
>>NCX-A supply ) that
>>hasn't been turned on in about 20 years.
>>I intend to bring it up
>>slowly to reform and avoid shock to the
>>old power supply electrolytics.
>>I have a 120vac variac, but none for
>>220, and I believe this should
>>work out OK, but what are the "gotchas"
>>involved? I feel that I should
>>remove the tubes as a precaution against
>>any possible damaging flashover.
>>Any suggestions from those who are
>>familar with this amp? Also
>>any loose 8122's around and available?
>>I'll want some spares if I keep it.
>>
>>Dick W0EX
>>
>>
>>--
>>FAQ on WWW: http://www.contesting.com/ampfaq.html
>>Submissions: amps@contesting.com
>>Administrative requests: amps-REQUEST@contesting.com
>>Problems: owner-amps@contesting.com
>>Search: http://www.contesting.com/km9p/search.htm
>>
>>
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