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3CX3000A7

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(Bob Marston)984325796Sun, 11 Mar 2001 15:49:56 +0000 (UTC)
GSeven wrote:

> I thought it would tune around at least 25pf bit its back all the way out.
> What should I expect to see with say 100 watts provided the tank is right?Answer  Not much   The 3CX-3000A7 is notorius as being a Pig to drive. The
spec sheet states that 410 watts is required to drive it to 2.0 Amps of
plate current. With 100 watts don't expect much more than 500 mils of plate
current with the tube biased correctly.

As to 10 meters not tuning that is also predictable. The 3000 has an
inordinately high output capacitance. 38pf  Compare this to the 8877 and
4CX-1500A which each have values of 10 pf and its understandable that you
are not able to tune 10 meters.

Finally the plate voltage that you state you are using (6700 volts) is a
full 33% over the manufacturers Maximum recommended Plate Voltage of 5000
Volts. BE CAREFUL !

It appears that Eimac intentionally developed this tune with the objective
of keeping it out of the hands of Hams and CBers. My recomendations, if you
have this Amp running on all bands but 10 declare victory and leave it
alone. Drop the Plate Supply to 5000 volts and limit the service of this
amp to 14 Mhz and below.

73s

Bob K1TA
(Mike Sawyer)984331759Sun, 11 Mar 2001 17:29:19 +0000 (UTC)
That to me, is sound advice!
Thanks Bob.
Mike(y)
W3SLK

----- Original Message -----
From: "Bob Marston" 
To: "G SEVEN" 
Cc: "AMPS" 
Sent: Sunday, March 11, 2001 10:49 AM
Subject: Re: [AMPS] 3CX3000A7GSeven wrote:

> I thought it would tune around at least 25pf bit its back all the way out.
> What should I expect to see with say 100 watts provided the tank is right?Answer  Not much   The 3CX-3000A7 is notorius as being a Pig to drive. The
spec sheet states that 410 watts is required to drive it to 2.0 Amps of
plate current. With 100 watts don't expect much more than 500 mils of plate
current with the tube biased correctly.

As to 10 meters not tuning that is also predictable. The 3000 has an
inordinately high output capacitance. 38pf  Compare this to the 8877 and
4CX-1500A which each have values of 10 pf and its understandable that you
are not able to tune 10 meters.

Finally the plate voltage that you state you are using (6700 volts) is a
full 33% over the manufacturers Maximum recommended Plate Voltage of 5000
Volts. BE CAREFUL !

It appears that Eimac intentionally developed this tune with the objective
of keeping it out of the hands of Hams and CBers. My recomendations, if you
have this Amp running on all bands but 10 declare victory and leave it
alone. Drop the Plate Supply to 5000 volts and limit the service of this
amp to 14 Mhz and below.

73s

Bob K1TA--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              
Administrative requests:  
Problems:                 
(Maurizio Panicara)984334157Sun, 11 Mar 2001 18:09:17 +0000 (UTC)
The 3CX3000A7 (and the descendant 3CX6000A7) can't give 2A plate with 100W
drive, but perfectly deliver >2KW out with 100W in and 6.7 Kv plate.
At 100W drive its gain is typically 13dB in Gg.
No way less power than 2KW if tube is OK and PI tank well designed.

73,
Mauri I4JMY


----- Original Message -----
From: "Bob Marston" 
To: "G SEVEN" 
Cc: "AMPS" 
Sent: Sunday, March 11, 2001 4:49 PM
Subject: Re: [AMPS] 3CX3000A7>
> GSeven wrote:
>
> > I thought it would tune around at least 25pf bit its back all the wayout.
> > What should I expect to see with say 100 watts provided the tank is
right?>
> Answer  Not much   The 3CX-3000A7 is notorius as being a Pig to drive. The
> spec sheet states that 410 watts is required to drive it to 2.0 Amps of
> plate current. With 100 watts don't expect much more than 500 mils ofplate> current with the tube biased correctly.
>
> As to 10 meters not tuning that is also predictable. The 3000 has an
> inordinately high output capacitance. 38pf  Compare this to the 8877 and
> 4CX-1500A which each have values of 10 pf and its understandable that you
> are not able to tune 10 meters.
>
> Finally the plate voltage that you state you are using (6700 volts) is a
> full 33% over the manufacturers Maximum recommended Plate Voltage of 5000
> Volts. BE CAREFUL !
>
> It appears that Eimac intentionally developed this tune with the objective
> of keeping it out of the hands of Hams and CBers. My recomendations, ifyou> have this Amp running on all bands but 10 declare victory and leave it
> alone. Drop the Plate Supply to 5000 volts and limit the service of this
> amp to 14 Mhz and below.
>
> 73s
>
> Bob K1TA
>
>
> --
> FAQ on WWW:               http://www.contesting.com/FAQ/amps
> Submissions:              
> Administrative requests:  
> Problems:                 
>
(Maurizio Panicara)984348304Sun, 11 Mar 2001 22:05:04 +0000 (UTC)
Incidentally, the output capacitance of a 3CX3000A7 in Gg is 24pf that's a
little bit more than twice the single 8877.
The 38 pf is not "huge" and anyway is the input capacitance.
A paired 8877, less that a single 3CX3000, would get more output capacitance
because of interconnections.
Last but not least, a reasonable PI with a loaded Q of 12 requires more than
the 3CX3000 internal capacitance and a vacuum variable capacitor
(raccomandable with such HV) has generally only 10 pf of residual
capacitance.

73,
Mauri I4JMY

----- Original Message -----
From: "Bob Marston" 
To: "G SEVEN" 
Cc: "AMPS" 
Sent: Sunday, March 11, 2001 4:49 PM
Subject: Re: [AMPS] 3CX3000A7>
> GSeven wrote:
>
> > I thought it would tune around at least 25pf bit its back all the wayout.
> > What should I expect to see with say 100 watts provided the tank is
right?>
> Answer  Not much   The 3CX-3000A7 is notorius as being a Pig to drive. The
> spec sheet states that 410 watts is required to drive it to 2.0 Amps of
> plate current. With 100 watts don't expect much more than 500 mils ofplate> current with the tube biased correctly.
>
> As to 10 meters not tuning that is also predictable. The 3000 has an
> inordinately high output capacitance. 38pf  Compare this to the 8877 and
> 4CX-1500A which each have values of 10 pf and its understandable that you
> are not able to tune 10 meters.
>
> Finally the plate voltage that you state you are using (6700 volts) is a
> full 33% over the manufacturers Maximum recommended Plate Voltage of 5000
> Volts. BE CAREFUL !
>
> It appears that Eimac intentionally developed this tune with the objective
> of keeping it out of the hands of Hams and CBers. My recomendations, ifyou> have this Amp running on all bands but 10 declare victory and leave it
> alone. Drop the Plate Supply to 5000 volts and limit the service of this
> amp to 14 Mhz and below.
>
> 73s
>
> Bob K1TA
>
>
> --
> FAQ on WWW:               http://www.contesting.com/FAQ/amps
> Submissions:              
> Administrative requests:  
> Problems:                 
>
(Jim Reid)984352822Sun, 11 Mar 2001 23:20:22 +0000 (UTC)
Aloha,

My Henry 8K amplifier is equipped with this tube, 3CX3000A7,
ceramic triode.

Per the factory test sheet which came with the unit,  it operates
as follows.  Keyed plate voltage is 5800 volts;  a bit over 6K
key up.

With a drive power of about 60 to 70 or so watts,  I get the full legal
1500 watts out on all bands,  160 up to,  and through 10 meter band.
At the factory the unit was tested into a big Bird dummy load and
produced:

100 watts drive;  2500 to 3000+ watts all bands.

10 meters, 250 watts drive, 5000+ watts out
15 meters, 215 watts drive, 5000+ watts out
20 meters, 200 watts drive, 5000+ watts out
40 meters, 230 watts drive, 5000 watts out
80 nmeters, 200 watts drive,  5000 watts out
160 meters, 275 watts drive, 5000 watts out.

In the SSB mode,  I have always rcv'd exceptionally good audio
reports,  obviously because of the great head room above our
legal power levels available from this set up.  A great amp
to operate,  I love it!!  Easy to tune as I have a number of
presets withit,  two or three for each band,  except on 20m,
where I am using 8 frequency tune/load pots set across the
band both CW, digital,  and US SSB areas.

73,  Jim,  KH7M
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