Date: Wed, 17 Nov 2010 09:11:33 -0700
From: "Fern" <crc@cyberlink.bc.ca>
Subject: [Amps] re compability of 3cx1200Z7 in lieu of 3cx1200D7eimac
Can one use an eimac 3cx1200Z7 tube in lieu of the 3cx1200D7 tube? I note that
the Z7 series has a flange at the bottom of the ceramic portion so will that
pose a problem for a swap? Also the grid pin is directly grounded! This is to
use at hf in a henry 3K Premiere amplifier. Any comments would be greatly
appreciated. Fern
## good question. The Z7 version is the best of the 1200 series. The
A7 and D7 are dogs imo. The big advantage of the Z7 version is it has the
least stray C, between anode and cathode.
The lower the anode to cathode C, the more stable the tube will be. Also, the
grid flange on the Z7 version is the best way to directly grnd the grid to
chassis. That too, will also promote stability.
I THINK that the Z7 version requires NO socket per se, [flange bolted
directly to chassis], but still requires the 2 x directly heated fil
connections. If that's the case, the fil connections would
have to be hardwired to the hot side of the bifilar fil choke. Also, with
that grid flange in place, you have to see how the airflow is going to work.
IF you removed the stock D7 socket, the grid flange
of the Z7 still has to be bolted to the chassis. You might require a new,
small AL plate, with a hole in the middle for the Z7 fil connections [ stem
part of tube], big enough, such that you can bolt the grid
flange to the new plate..and also have the plate big enough that it's outer
circumference can then , in turn, be bolted to the existing chassis. It sound'
like a lot, but it's straightforward really. You
also nned slots/holes in the new small plate, for the airflow.
## It would be very similar to using any other tube that has a built in grid
flange, like a YC-156 or YC-243. When you really look at it, sockets on HF
are a waste of time..on any GG triode. All you have
is the fil/grid and anode. The grid is bonded to chassis. A simple built in
grid flange and a pair of fil lugs is all that's required. The megabuck
socket [esp on big triodes] is extra money. I went a few go arounds with
Eimac on this subject years ago. They did come out with a socketless 3x20,
called a 3CX-20,000C7..and also a YC-243 [socketless 3x6 /YU-148]. The
1200Z7 was another one. They shoulda done the same thing
with the 8877, and the rest of the GG triodes. It does take longer to change
a tube out though, but not an issue, since tubes rearely get changed out
anyway.
## You will see that Eimac sells these emergency replacement socket repair
kits for the bigger tubes. A local broadcast eng buddy of mine sez he has
seen SK-300A sockets that end up burnt to a crisp,
burnt finger stock, etc. [ those are tetrodes, and do require a socket]. The
SK-1320 is the GG socket for the 3x10/15/20 triodes....cost huge $$...and
is a prime candidate for a socketless version.
## if your 1200Z7 tube is in good conditon, it may well be worth the 'easy'
conversion from the D7. Dunno what the future availability of the Z7 is
though.
later........... Jim VE7RF
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|