[Amps] Pi-L Network Question

[donroden at hiwaay.net]

Are you saying that the coil(s) are larger to go from 2600 ohms down  
to 200-500 is larger than going from 2600 down to 50 ?

Don W4DNR


Quoting Jim  Garland <4cx250b at muohio.edu>:

> You're right, Peter. I misspoke. It's the large required L1 & L2 that make a
> pi-L impractical for an 8877 on 160m. For example, for Q=12 and a plate
> impedance of 2600 ohms (roughly correct for an 8877 with 4KV plate voltage),
> L1=43uH and L2=11uH. L1 would truly be a monster inductor! For a pi-network,
> L1=23 uH, or roughly half as great as for a pi-L. The values of C1 and C2
> aren't really of practical significance, since one can always use fixed
> capacitors as needed. Thanks for correcting me.
> 73,
> Jim W8ZR
>
>> -----Original Message-----
>> From: Peter Voelpel [mailto:df3kv at t-online.de]
>> Sent: Monday, June 18, 2012 11:03 AM
>> To: 4CX250B; amps at contesting.com
>> Subject: RE: [Amps] Pi-L Network Question
>>
>> It´s the opposite.
>> The required capacitance of the load-C of a simple Pi network is much
> larger
>> then that of a Pi-L, a big advantage beside the much besser harmonic
>> supression and easier tuning.
>> The two coils should not couple to keep the harmonics as low as
> calculated.
>> However, the required inductance is larger with the Pi-L.
>>
>> 73
>> Peter, DJ7WW
>>
>>
>> -----Original Message-----
>> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
>> Behalf Of Jim Garland
>> Sent: Montag, 18. Juni 2012 17:57
>> To: amps at contesting.com
>> Subject: [Amps] Pi-L Network Question
>>
>> I've been noodling around various tank circuit possibilities for a 160m
>> monoband amplifier. A pi-L network isn't very practical for an 8877
> because
>> the relatively high plate impedance mandates very large values of C1 and
> C2.
>> For an 8877, a simple pi-network is preferred. On the other hand, a Pi-L
>> makes a lot of sense for, e.g., three 3CX800a7s or GU-74Bs,  because the
>> combined plate impedance is under 1000 ohms and the required capacitance
> and
>> inductance values are quite reasonable.
>
>
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