Clarification please:
The current Eimac webpage says that the socket is the *same* for both the
3cx1200a7 and 3cx1200z7 (SK-410). Several posts said that the socket was
different. Is this a web page misprint or are the sockets still the same?
The only other cooling related difference (again from the web page) is that
the a7 requires a chimney (sk-436) and the z7 does not. (or so it would
appear.)
Is that correct?
I take it that the a7 has generates little sales volume for Eimac, and so
would likely retired earlier than some other tubes. Is the same true for the
1200z7?
I ask this because because several responses indicated how much better the
'z7 was in my response to my 'product lifetime' question that I wonder if
there is an implication taht the z7 will be around longer than the a7.
Finally, if the socket is the same, and I were to change the filament
voltage, what else woudl have to be done to use an z7 as a replacement for
an a7 in an amateur HF linear. (I see the anode connection is different).
Thanks
Ed
----- Original Message -----
From: "rlm" <r@somis.org>
To: "Dave Haupt" <emailw8nf@yahoo.com>; "AMPS" <amps@contesting.com>
Sent: Friday, October 24, 2003 12:15 AM
Subject: Re: [Amps] Re: Future availability of 3cx1200a7 and 3cx1500a7?
>
> On Thursday, October 23, 2003, at 05:06 PM, Dave Haupt wrote:
>
> > Ed,
> >
> > The difference between the '1200 and '1500 in feedback
> > capacitance is only 2:1,
>
> *** There is apparently a typo in Eimac Catalog 175. The correct
> anode-cathode C for a g-g 3cx1200A7 or 3-1000Z is c. 0.2pF, so Dave
> Haupt is correct. The anode-cathode C is 0.1pF for a g-g 8877 (Eimac,
> 5/15/1977). The anode-cathode C (g-g) for a 3cx1200Z7 is 0.075pF
> (Eimac #2209).
>
> > and both are very small,
> > indeed. While there are the occasional reports of
> > oscillations with the '1200, it is more likely a
> > result of the long element leads inside the tube, and
> > not a result of the 0.2pF feedback capacitance.
>
> **** Can 0.2pF of feedback be dismissed as insignificant? '
> - At a freq of 110MHz, 0.2pF has c. 7k-ohms of XC. With an anode
> supply potential of 4000VDC, the AC current through C-feedback is
> 0.385A. In my opinion, it would not be good engineering practice to
> ignore this.
>
> > The
> > 3CX1200A7 data sheet shows the in/out/feedback
> > capacitance when operated in grounded cathode, and
> > Rich appears to have not converted that data into
> > grid-referenced data.
> >
> > However, the feedback capacitance information has
> > absolutely nothing to do with your original question.
> >
> > Were it my amplifier, I would choose the 3CX1500A7
> > immediately. I have seen the 3CX1500A7/8877 used as a
> > driver in many broadcast applications, and as a final
> > in many scientific applications. I have never seen a
> > 3CX1200A7 outside of a ham amplifier, ever. The 8877
> > is popular enough that, at least at one time, it was
> > available from Chinese sources.
> > The 8877 is available frequently as a medical pull
> > for $300 or so. WA8WZG usually has them offered on
> > his website.
> >
> > 73,
> >
> > Dave W8NF
> >
> >
> >
> > Rich wrote:
> >
> > **** The problem with the 3cx1200A7 (and the 3-1000Z)
> > is that it has
> > roughly 7x
>
> **** this should read 2x as much ... ...
>
> >
> > as much feedback-C (Anode-cathode C) as an
> > 8877. Although
> > more feedback-C is beneficial in VHF oscillators, it
> > can be a problem
> > in HF amplifier applications. To reduce feedback-C,
> > Eimac came up with
> > the 3cx1200Z7. It has about 1/10 as much feedback C
> > as the ...A7. The
> > cost is c. $20 more than an ...A7, it uses a 6,3v
> > filament, and it
> > requires a better-design socket, so it is not a
> > plug&play substitute..
> >
> > cheers
> >
> >
> > On Tuesday, October 21, 2003, at 06:09 AM, Ed Briggs
> > wrote:
> >
> >> I was wondering if it is possible to predict how
> > long the 3cx1200a7
> >> will continue to be available from Eimac. I'm
> > considering buying a
> > new
> >> amp, and pondering the future availability of the
> > 3cx1200a7,
> >> 3cx1500a7, and of course the Svetlana 4cx800.
> >>
> >> Is the 3cx1200 widely used? I know of two amateur
> > amps in production
> >> with this tube, and I wonder if there are
> > non-amateur applications.
> >>
> >> It seems the 3cx1500a7 is more widely used in
> > non-amateur
> > applications
> >> and thus might be a longer survivor. Also, it seems
> > to have a second
> >> source.
> >>
> >> Anyway, if anyone has guidance, particularly wrt.
> > the 3cx1200, I'd be
> >> very grateful indeed.
> >>
> >> Ed
> >> N1TS
>
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