[Amps] L-PI amp network

[Steve Bookout]

Hello all,

(First part is background, so you know a more 'overall' of what I'm doing.)

I've been intending to finish a long-ago-started mono band amp for 10 
meters, and I think I regained the enthusiasm I need to complete the 
project.

I had started out going to use a pair of grounded grid config 4-400's 
only BECAUSE I HAVE A BUNCH.  That was then, this is now. I've recently 
found a treasure trove of 8877's and have determined that I have SIX of 
them!

With the exception of one, all were unknowns, so I 'cooked' them on fil 
voltage only for a day, and then applied the B+.  My test platform as a 
HB 8877 40 meter amp that I built in the mid 80's. It still uses the 
same tube.  Peter Dahl 3000 volt 6 KVA transformer, for 4000 volts.   22 
watts drives it to 1500 out; ~ 600 ma/.030 grid.

Over the period of about a week, I cycled all of the unknown tubes thru 
this amp.  They all were similar, taking 22 to 27 watts of drive for the 
same 1500 watts out;  550 ma to 600ma @.030 ma grid.

That was the background for my real question for the group.

Based upon GM3SEK's PI/PI-L calculator, I'm working with a plate load 
impedance of ~3000 ohms.  I know from my own experience, and that of 
others, that it's a pain to get the plate inductor 'right' so that it 
all works and tunes, as it should and make power with reasonable 
efficiency.

I have never used an L-Pi, but I basically understand the idea.

IS THERE A RECOMMENDED TOOL OUT THERE, WHICH WILL HELP ME FIGURE OUT MY 
TWO "L's"?

Using GM3SEK's calculator, I see there is a line, 'Lead inductance 
(total from tube to tank, but excluding suppressor)', which I have 
played with.  Adding my 'L' inductance there, say '.6uh', does reduce 
the inductance associated with PI, and it does raise the value of the C1 
capacitor.   ( I am using a 100 pf /15 KV vacuum variable and right now 
as I write this, I don't remember it's minimum C, but it's in the range 
of what I think you should see; maybe 5 pf?)  Using this, I was able to 
come up with about 15 pf, vs 4 pf in a standard PI configuration.

Suggestions on if this would be an accurate way to figure this out?   
Or, another/better way?   And, what should I be looking for as maybe a 
ratio of the 'L' vs the 'L' in the PI network.   As I recall, I think 
I'm looking at about 1.7 uh.

I would appreciate any constructive comments, or even precautionary ones.

73 de Steve, NR4M