Funny, I didn't see you over my shoulder while I was reading your post. I
read the entire thing, both then and now.
I was quoting Ted Henry. I didn't have the conversation with Eimac.
As for the 3CX1200A7 having a problem in some other brand of amplifier, OK,
I'll take your word for it. Let's put it as more the manufacturer than the
tube.
As for HENRY using this tube in their HF amps, it is an excellent performer
and VERY stable!
My HENRY 3K Classic X MKII (using a 3CX1200A7) will put out into a 50 ohm
load 2500 watts on 10M with drive that still doesn't push grid current to
tube max ratings.
Hmmmm, with these "extra losses at the high end of the HF spectrum" I would
say it must be "properly tamed" eh?
As if there is some shame in stating facts about HENRY amps. I have no
problem with it pertaining to this question about tube choices.
I agree that at higher frequencies there are better tube choices, but for
10M and lower this tube in the proper hands plays very well.
73, Dan Magro W7RF, (member SCDXC, SCCC)
Rugged, Reliable Henry HF Amps are "Instant on" for RF Power now!
DXers/Contesters/Ragchewers get your HENRY from RADIODAN for LESS!
***Subscribe to the HENRY reflector at www.qth.net <http://www.qth.net>
***
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> -----Original Message-----
> From: owner-amps@contesting.com [mailto:owner-amps@contesting.com]On
> Behalf Of Bob Marston
> Sent: Wednesday, October 07, 1998 9:42 PM
> To: amps@contesting.com
> Subject: RE: [AMPS] What Tube for Home brew
>
>
>
>
> 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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>
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