[Amps] L-PI amp network

[Jim W7RY]

What plate voltage are you going to have on the tube of choice Steve?

Jim W7RY


On 12/13/2022 4:36 PM, Steve Bookout wrote:
> 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
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps

-- 
Thanks and 73, Jim W7RY