[Amps] Two quick loading questions

[R.Measures]

On Feb 10, 2005, at 11:23 AM, Gary Schafer wrote:

> It is not always easy to see flattoping on a scope.

Amen, Gary.  The best way to measure total IMD is with a step-attn set 
and a  double-filter Rx tuned to the adjacent frequencies.

> Especially when using any kind of speech processing. The processing 
> itself tends to square off the peaks. So when you actually observe 
> flattoping on the scope you are probably well into it.
>
> 73
> Gary  K4FMX
>
> Rob & Terri Sherwood wrote:
>> I have always been puzzled by the "maximum smoke" tuning 
>> recommendations of some amps, AL-80A or B, for example.
>> A single 3-500Z in linear service is rated at 400 mA plate current. 
>> (350 mA in class C).
>> When I used to run a Measures/Kessler modified TL-922A (pair of 
>> tubes), I tuned it as follows:
>> 800 mA on the plate and 150 mA on the grid for SSB.  If I was running 
>> CW, I tuned it for 200 mA on the grid.
>> It was very easy to adjust the plate tuning for a grid current peak, 
>> as opposed to trying to see a broad plate current dip.
>> When tuned for the 800/150 mA conditions, the amp was very linear at 
>> 800 mA, and would saturate at something approaching 900 mA.
>> I always monitor my amps with a Tektronix scope, and set the RF 
>> envelope at 6 divisions at the above plate/grid current conditions.
>> With a modest amount of speech processing to control the peaks from 
>> the exciter, it is easy to see the linear flattop a bit above the 6 
>> scope divisions.
>> Set the drive on the exciter to peak the amp at 6 divisions, and I am 
>> completely confident I have a clean signal.
>> Without a scope, it is difficult to know how hard to drive the amp.  
>> The ballistics of analog meters is all over the map.   My Alpha 76PA 
>> was very different from my TL-922A meters. My present Alpha 99 and 89 
>> amps, even with LED metering, are not peak reading devices.  In these 
>> two Alpha examples, if the power output is set for 1500 watts key 
>> down, the LED meters read about 800 watts on voice peaks.
>> R.Measures wrote:
>>> Tuning for max P-out with max-drive is more important than looking 
>>> for a dip.
>>>
>>> On Feb 9, 2005, at 12:39 PM, George KB2Z wrote:
>>>
>>>> I'm sure I'm not the first to ask. I have searched in the archives 
>>>> and did not find a solid answer. I apologize up front and am not 
>>>> trying to waste anyones time. The directions from different  
>>>> manufacturers dont seem to answer one way.
>>>> As I read the loading instructions for gg hf amps, (2x3-500) they 
>>>> should be fully loaded at full power then the loading increased 5 
>>>> to 10% to lower the Ig and help stabilize the output. This seems to 
>>>> be where it gets confusing for me.
>>>>
>>>> 1) After increasing the loading 5 to 10%, should the plate be 
>>>> re-dipped?
>>>> 2) If drive is reduced from 100 to 50W, should the plate be 
>>>> re-dipped.
>>>>
>>>> Thanks in advance,  George KB2Z
>>>>
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
>>>>
>>>
>>> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
>
>
>
>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org