Don't believe the 1.8.
I found that this is far from the correct value for the 4CX1000A. Maybe it's closer for
triodes like 8877s, maybe not.
See
<http://www.granta.g4axx.com/Linear_design_notes.php3>
for an example of how to determine the load impedance from the the constant current curve
for the tube. Here's an 8877 datasheet which contains those curves:
<http://www.g8wrb.org/data/Eimac/3CX1500A7.pdf>
On 10/20/2013 1:37 PM, Jim W7RY wrote:
Jim...
To figure the plate load impedance:
RP = EP / 1.8 X IP
1.8 = K factor for class AB1 (Changes with ZSAC)
RP = Plate Resistance
EP = Plate Voltage
IP = Plate Current
1.8 X .65 Amps = 1.17
1.17/ 4000 = 3418 Ohms plate load impudence.
Your actual voltage will more likely be 3800 with a .65amp load which brings
the load down
to 3250 Ohms.
Better to just switch in some loading padders with your bandswitch.
See the last 8 years of the ARRL handbook for the K8RA amplifier using the
3CX1500D7 tube.
There are some great examples there.
73
Jim W7RY
On 10/20/2013 8:28 AM, Jim Barber wrote:
1500 watts
4kV, 625mA
Single 8877 at around 4000 ohms plate impedance in AB2.
Tnx,
Jim N7CXI
--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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