At 02:31 PM 10/7/98 -0700, you wrote:
>In reference to the question on the 3CX1200Z7 tube:
>I asked Ted Henry about the 3CX1200Z7 and he called Eimac and I quote
>"Eimac swears to us that the 3CX1200Z7 is not being discontinued. "
Hello Dan
I see you stopped reading my post after the the first sentence in the
second paragraph. I don't know who Ted Henry spoke to at Eimac. I spoke
with Reid Brandon of the engineering staff. To be explicit he informed me
that production of the Z7 variant of the 3CX1200 ceased when production was
transferred from Utah back to California. Production resumed in California
with a new anode cooler and the the tube was reassigned the commercial
designation YC229. The new cooler will permit 1600 watt plate dissipation
with a 3-3/4 squirrel cage fan turning at 3200 rpm thus the 3CX1600Z7
designation. Mr Brandon also told me that distribution of the tube was
being done through Howell Engineer in Columbus, Ohio. As the anode cooler
is the only difference between the 2 tubes a 1200Z7 equivalent is in
production. The A7 and D7 variants were not affected by these decisions and
are readily available.
>The 3CX1200A7 as used in the HENRY 3K Classic & Premier and 5K Classic, as
>well as the 3CX1200D7 as used in the HENRY 3KD Premier
Ahh Dan I knew you couldn't pass up the oppourtunity to plug your/Ted
Henry's equipment.
Yes the 1200 series is a much more rugged tube than the 8877/3CX1500A7.
This is to its credit. But like a salesman you fail to mention a short
coming of the tube. The A7 and D7 have an internal structure that make it's
base pin configuration identical to the 3-500Z. Allowing the use of the
SK-410 air system, socket/chimney. This internal configuration came
complete with a higher than typical interelectrode capacitance. This
results in a tube that breaks into Parasitic Oscillation at a lower than
normal frequency. About 100mhz is typical. Taming this tube while not
difficult does result in extra losses at the high end of the HF spectrum.
Specifically 10 meters. There have been a number of posts on this list
regarding reduced efficiency of AL-1200s on 10 and 15. The AL-1200 does use
the 3CX-1200A7. The changes in the D7 did not address this problem to any
appreciable extent. Eimac then did some redesign on the internals and came
up with the Z7. There are only 3 pins on the base. 2 heaters and 1 grid
pin. The most important grid contact is the grid ring that is new on the Z7.
In the same phone conversation with Reid Brandon I asked about a socket for
the Z7 tube. He gave a detailed response of an elaborate socket that is
used in MRI equipment. It was unnecessarily complex and he gave a simple
and cheap alternative. The grid ring has 4 studs. Cut a hole in the chassis
to allow the base of the tube pass through and drill out 4 holes for the
grid ring studs. Mount the tube by securing the studs with nuts. For
cooling you will have to pressurize the entire upper compartment and
exhaust the heated air through a suitable chimmney out the top. For the
filament blowing air directly on the pins from any axial fan capable of
generating 20 cfm in free air would be sufficient. For filament and grid
pin connectors it is necessary to obtain the clips from a 410 socket and
solder them the choke leads. He stated DO NOT solder directly to the tube
as this would destroy the seals.
Well I will leave it at that for now. I been curious about the 3CX1200Z7
because of the 1200s durability and my desire for a solid 10 Meter Amp.
Because I am a 10 Meter fanatic I would not buy any amp with a 1200A7/D7
tube. And there are no commercially made 1200Z7 amps. There is a QST
article detailing the construction of a 50Mhz amp around this tube by
N7ART. Happy building
Bob Marston K1TA
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