I bet you won't need much series L. The Cout in GG of the 8877 is only
10pf.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 12/13/2022 8:38 PM, Steve Bookout wrote:
Thank Jim,
One of my big questions was if I could use GM3SEK's spreadsheet
calculator. I'm not too far off from what you came up with and that
was because we used different numbers here and there.
I've got a brand new 50 ft coil of copper tubing to use up. In the
past, I've used solid #4 copper (3/16 inch dia) but too hard to work
with and it work hardens terribly. I'm winding it, by hand, on a
form on a lathe.
Again, thanks for the input.
Steve
On 12/13/2022 9:18 PM, Jim W7RY wrote:
Here is what I come up with... ~3000 ohms plate load impedance.
Oh..... I cant attached to this group!
But you can see it Steve since I copied you directly. The results are
highlighted in yellow.
73, Jim W7RY
On 12/13/2022 5:23 PM, Steve Bookout wrote:
Hello Jim,
4kv. It's about 4.2 kv, no load.
On another point, for the group, 'somewhere, sometime', in more than
one place on the web, I've seen where people recommended using 2.0
as the 'K' factor, instead of 1.5-1.8, etc. This was specific to
8877's. I used 2.0, as I very, very rarely use a microphone.
Just wondering
Steve NR4M
On 12/13/2022 6:01 PM, Jim W7RY wrote:
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
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