[Amps] 8171

[jeff millar]

Barrie...

Here's some design ideas, based on a smith chart analysis using the 
gsmc-1.1 program, assuming 25 pF output capacitance and 3K plate load 
impedance (with strays).  I can run the numbers for different Cout or 
plate load if you like. 

Overall, I like Network 2 for lowest Q and smoothest tuning.

Network 1
L1,  series, 488 nH
C1, parallel, 190 pF
L2, series, 194 nH
C2, parallel, 107 pF
This network has the additional advantage that the load control (C2) 
doesn't affect tuning (C1)

Network 2
L1,  series, 437 nH
C1, parallel, 243 pF
L2, series, 83 nH
C2, parallel, 63 pF
This network has the additional advantage that the load control (C2) 
doesn't affect tuning (C1)

Network 3, no L1, small C1
L1, series, 1 nH
C1, parallel 8 pF
L2, series, 345 nH
C2, parallel, 244 pF
This network is high Q and touchy to tune

Network 4, Tune and load caps less than 100 pF
L1, series, 584 nH
C1, parallel, 78 pF
L2, series, 504 nH
C2, parallel, 47 pF
If you have two of the cheap 100 pF vacuum variables, low Q, tune and 
load interact.

Hope this helps...

jeff, wa1hco

Barrie Smith wrote:

> I'm still muddling about trying to find a workable solution for 
> getting an 8171 on 6M.
>
> The tube's internal capacitance is a big problem.  I've posted this 
> whine previously, and have not gotten any real solutions.
>
> Also (not from this list), I've gotten the suggestion to run both 
> grids grounded and run without a screen supply.
>
> Is that a possibility?
>
> Barrie, W7ALW
>
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