[AMPS] 3CX1200

[Ken Barber]

George,
  Thanks for the information.  The 3CX3000A7 looks like an excellent tube.
  Some have suggested using an 8877 which is a nice tube, however, I have
both the AL-1200 and the AL-1500.  When I drive the AL-1500 with 20 watts
of carrier on 75 AM and setting it up with a single tone using a scope, the amp
puts out approximately 400 watts carrier, 1600 watts PEP tone.  While talking
everything is fine, however, if I accidentally hit the mike stand (rare
occurrence),
the audio spike kicks out the 8877 overload and I'm back to 20 watts.  The
AL-1200 (modded with 3800 volts under load) can put out the same power
and is not as sensitive on overloads, perhaps because it has twice the grid
dissipation over the 8877.   If I were strictly on SSB with low drive power,
I think the 8877 would be my tube of choice and if I wanted to step up to
another level and had sufficient drive the cathode driven 3CX3000A7
would, in my opinion, be a superb choice.
  I received another response that indicated that the 3CX1200Z7 would have the
least amount of parasitic problems as compared to the 3CX1200A7 so I'm now
thinking about a rig with that tube.
  Thanks for the response and the information.
73,
Ken W2DTC
--------------------------------------------------------------
George Benko wrote:

> Hi Ken,
>
> Interesting question.
>
> The A7 and Z7 are electrically the same tube.  The only differernce is in
> the grid ring. The Z7 has a solid grid ring for operation at higher
> frequencies.  Electrically, it has 7.5V filament @ 21 amps.
>
> The D7 is a slightly different critter. The filament is 6.3V at 23 amps and
> the cooling is slightly larger diameter.
>
> I don't have the data sheets in front of me, but I believe the internal cap
> is about the same. Specs on the D7 are not as well defined for HF SSB so I
> really can't say on IMD.
>
> Given the above, I would say they are all about equal at HF.
>
> I have built such an amp in the past and was somewhat not satisfied.  It was
> hard to drive, used double the parts, etc. IT did fit in an L4B deck though.
> (Very easy conversion from 3-500s) with a DAHL filament transformer.
>
> Another alternative to consider might be to use a single 3CX3000A7 or F7.
> The F7 does not need a socket. The filament is 7.5V @42 amp (same as a pair
> of the above), is a single tube (easier to build), pulls are about the same
> cost or less than a pair of the A7s pulls, and the real kicker is it is the
> cleanest tube around for IMD.
>
> All of the above are "instant on", great for when that DX station pops out.
>
> My thoughts only,
>
> 73, George
> K8BRW
>
> ----- Original Message -----
> From: "Ken Barber" <kbarber@monmouth.com>
> To: "AMPS" <amps@contesting.com>
> Sent: Monday, October 09, 2000 5:39 AM
> Subject: [AMPS] 3CX1200
>
> The 3CX1200A7, the 3CX1200D7 and the 3CX1200Z7 have similar ratings. I
> would like to build a two tube 160-10 linear around one of these types.
> Which one seems to be the best and why?
> Thanks,
> Ken Barber
> W2DTC
>
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