[VHFcontesting] 222 amp

[David Pruett]

Dana,

I may be wrong, but I seriously doubt that is an issue. The difference 
between 220 and 222 MHz is only one percent and the plate output circuit 
has plenty of adjustment range to handle the difference.  The grid 
circuit is formed with lumped inductances that probably have more than 
1% tolerance, but can easily be adjusted by squeezing or expanding the 
inter-turn spacing.

Dave/ K8CC


On 12/31/2014 11:46 AM, VE3DS wrote:
> The original design from 1980 may have been for 220 Mhz rather than 222 MHz…so
> grid and plate lines may need some trimming?
>
> Dana VE3DS
>
>
>> On Dec 31, 2014, at 10:37 AM, David Pruett <k8cc at comcast.net> wrote:
>>
>> Mike,
>>
>> According to the description of the 220 MHz W6PO amp in W6SAI's Radio Handbook, here are the operating conditions with 3000V on the plate:
>>
>> Single tone plate current            667 mA
>> Idling plate current                  54 mA
>> Cathode zener voltage                 12 V
>> Single tone grid current              48 mA
>> Power input                         2000 W
>> Power output                        1230 W
>> Apparent efficiency                   61 %
>> Drive power                           48 W
>> Power gain                            14 dB
>>
>> With only 20-25W drive, one might expect numbers roughly half of these levels.  Presuming you are using a 100 mA grid current meter, I would think you'd easily see 25 mA of grid current and only about 333 mA of plate current.  Tube age and "goodness" could shift these numbers somewhat.  Still, I think you're seeing too little grid current and slightly high plate current. This seems to indicate too heavy loading of the amp.
>>
>> Dave Olean's advice to move the loading plate away from the tube is the right thing to do.  Apply drive power carefully, dip the plate tuning and note DC power input and RF output.  Move the loading plate a little closer to the tube and repeat the process, possibly with a little more drive to keep the grid current in the 30-50 mA range.  You should see increasing power output with roughly 60% efficiency (RF output/DC input).  When the efficiency starts to drop off, you've gone too far.
>>
>> Dave/K8CC
>>
>>
>>
>> On 12/31/2014 8:19 AM, Dave Olean wrote:
>>> I show very little grid current. Roughly 3000 volts .500 mill of plate current 1500 in 200 out. 20-25 watts drive Ft736 driver. Mike
>>>
>>> Those readings seem ok. I would think that 20 watts would drive it to 500 ma. I would make sure that you could move the plate loading "plate" far away from the tube. Are you sure that the plate circuit goes thru resonance? Maybe it never does! You might check that too. Use a grid dipper or antenna analyzer.
>>> If the loading control has little effect, I would also try looking at the input with some sort of return loss bridge or antenna analyzer. You could also put a Bird 43 type instrument in and see what the VSWR looks like when you apply drive power. I remember I had a problem with my new amplifier and it was a poor connection on a ground on the input circuit around the tube socket. The input impedance changes with drive level, so a VSWR check is only valid when the amp is being driven with RF, but you should still see some sort of poorer match with almost no drive.
>>>
>>> Dave K1WHS
>>>
>>> ----- Original Message ----- From: "mike repinski via VHFcontesting" <vhfcontesting at contesting.com>
>>> To: <vhfcontesting at contesting.com>
>>> Sent: Wednesday, December 31, 2014 4:16 AM
>>> Subject: [VHFcontesting] 222 amp
>>>
>>>
>>>> One other observation. The controls do not seem to operate as sharp as my 2 meter amplifier does. Kind of sluggish. The loading does not seem to do much. Mike WB8PFZ
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