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
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