R: [AMPS] L-Pi net...downside?

[Rich Measures]

>
>Hams are meant to use grip-dip meters and not worry about "Q" factors.
>On the input circuit (amp "OFF"!), get the deepest dip (check the
>harmonic response), on the output circuit, check for dips across the
>widest frequency range while twiddlying the "load" and "tune" caps. Then
>hope that the tube's input and output impedance doesn't change much as
>soon as its switched on. 

€  Pi-networks and L networks are not resonant on the working frequency.  

>If any dips (other than a nice deep one at the wanted response) are
>noted, Murphy dictates that in the heat of a contest, that combination
>will be tuned by the operator, then possibly bye bye amp.
>
>To tune the thing, if all seems in order:
>Leave the ouptut tuning on best match found, switch on and warm up,
>twiddle the input tuning a bit (exciter's automatic tuner OFF) while
>keeping a beady eye on the location of the HV post, the exciter's full
>power output, the exciter's SWR, and the amp's power output by tweaking
>the "load" and "tune" caps. Compromise for best output power vs input
>SWR. Go and have a cup of coffee while the old nerves unjangle, count
>yourself lucky to have survived such a frightening ordeal.
>Ian, ZS6BTE
>
>Maurizio Panicara wrote:
>> 
>> Vic,
>> 
>> with some care and a bit of experience in correct positioning and wiring,
>> the problem to find or realize proper components to have and keep a
>> standard PI network whose loaded Q is 10 is a fake one.
>> The problem is that on 10m the residual of plate capacitor plus tube/s
>> internal plate capacitance in some cases are so big that the first usable Q
>> is not 10 but a much higher value. In that case it's really hard to find out
>> the proper components (coil) and do not destroy Q with multiband amps
>> related items like wires (even short) and/or switches (even small).
>> If the practical situation allows the design of a PI whose loaded Q is 10
>> and no other parameter is required such network is a totally superflous
>> complication.
>> Go ahead with a symple PI network.
>> 
>> 73,
>> Mauri I4JMY
>
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Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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