[Milsurplus] [ARC5] Hello Smart People: Output Network "L"

[C.Whitaker]

de WB2CPN
Is the PA output the usual Pi network, a capacitor, the
coil, and the other capacitor?  Or is it something else?
How is the "something else" wired?
73  Clete
++++++++++++++++++++++++++++++++++++++++



On 4/14/2012 1:55 PM, J. Forster wrote:
> Does the transmitter have a variable coupling, like a rotating link?
>
> If you don't have effectively a variable ratio transformer between the
> tank and the load, you can have a mismatch.
>
> Changing the choke inductance, changes the impedance at resonance, despite
> changing the capacitor too.
>
> In a resonant circuit, there are two things you can vary, L and C. These
> control two other parameters, the resonant frequency and the impedance at
> resonance.
>
> What matters is the match between the tank at resonance and the load.
>
> -John
>
> =================
>
>
>
>> I learned the lazy-man's way (tinkering) just
>> how critical to PA stage efficiency and output
>> is getting the right value of "L" in the output network.
>> A single turn in a "Pi" net can make a large difference
>> in how much you get out vs. how much you put in.
>>
>> While working on the RAAF AT5 transmitter,
>> I was getting 12 AM watts out in R/T, just as specified.
>> CW output was a little lower- about 35 watts.
>> But in AM I was seeing 100 mills into those two 807s.
>> That's 55 watts in for 12 out unmodded carrier... hmm.
>>
>> The output for the AT5 is designed for 100 ohms
>> and normally feeds a tuner.  I was using, of course,
>> a 50-ohm load, feedline and wattmeter
>> (The original antenna connector is broken, so
>> I've temporarily mounted an "N" connector there).
>>
>> I got to thinking of my "lessons learned" while
>> building "Old Fireball (1935 RK20 rig)"
>> I dug-out a very short screw with course threads
>> and "screwed" it between two turns in the PA output inductor-
>> the turns between the two first vertical taps from
>> the front of the coil- effectively removing a turn.
>> After re-tuning, I still have .100 mills on AM,
>> but now the rig has 25 watts of clean, grid-modulated
>> carrier out and on CW, 50+ watts.
>>
>> So, for the dozens of you smarter than me,
>> here's the question:
>>                                Why?
>>
>> 73 DE Dave AB5S
>>
>> P.S. Australian folks:
>> If any of the AWA engineers still live, please tell them I'm
>> going to have one to their health. These are neat radios.
>>
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>
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