[Amps] Re: Future availability of 3cx1200a7 and 3cx1500a7?

[Dave Haupt]

Ed,

The difference between the '1200 and '1500 in feedback
capacitance is only 2:1, 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.  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 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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