[Amps] L-PI amp network

[Steve Bookout]

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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