[Amps] 200-ohm tank and "un-un" in HF amp design?

[Jim W7RY]

Ummmm... He's using an 8877.

73
Jim W7RY

On 10/20/2013 9:56 PM, Vic K2VCO wrote:
> 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
>