[Amps] L-PI amp network

[Jeff Blaine]

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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>>>>
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