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Old 3rd November 2007, 07:13 AM   #1
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Default 15E and plate curves

I wanted to used the 15E in a future project/gift and I've searched high and low for curves for this little guy. As far as I can tell they don't exist. So I was wondering how do people go about making their own plate curves in this situation? What equipment would I need? What kind of setup? Am I wrong and plate curves do exist for this tube?
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Old 3rd November 2007, 02:24 PM   #2
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Default tube curves

A 2 part answer

Part 1) General method
I use a regulated power supply and a breadboard set up with the correct tube socket. I use multimeters for plate voltage, plate current, Screen voltage, screen current and grid voltage. I manually sweep the plate voltage and read the currents, and step the screen voltage etc. Some people may automate all this.
I use various spreadsheets to collect the results and model the tubes.

Part 2) Reality Check
This "little guy" operates with 7.5K to 10KVolts plate to cathode, handles pulses up to 15KV and outputs 10KW. The filament current is 4A. You probably already know that, but my point is it is not a tube I personally would be fooling around with using the cobbled together equipment I use described in part 1).

I suppose you could use the tube at "normal" voltages ie a couple of hundred volts and see what it does.
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Old 3rd November 2007, 03:43 PM   #3
mwiebe is offline mwiebe  United States
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Some where floating around there are plate curves that someone generated, probably Dave Slagle. You could ask on his Intact Audio forum.

And I think he also generated these for the 3C24 which should be close to the 15E. Rp around 13K for a 600V, -12.5, 17ma operating point and 14K for 400V, -6.25, 13ma and in both cases the gain is about 22. I appoligize if the data is someone elses but it's probably a ball park to start in.
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Old 3rd November 2007, 04:35 PM   #4
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McLean
Yah I knew the military ran them at those voltages but I read about some projects (mainly ham radio but one amp) where people ran them between 1-3Kv.

mwiebe
Thanks for suggestion to ask on Intact Audio. I already did a quick search and it looks like a few people there have used them so maybe someone did plate curves.
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Old 3rd November 2007, 04:56 PM   #5
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If the 15E is similar to the 3C24 then you should look at the Yahoo group called GM-70. Theres been a thread about using them and trying to revive some that went gassy.
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Old 4th November 2007, 03:41 AM   #6
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what I have found for spec data online:

Mu=25
plate dissipation = 20W
filament = 5.5v@4.2a
max voltage = 2Kv (for MOST applications it can be WELL over that for certain tasks apparently)
max current = 63ma

also so measurements some guy Jeffrey made: (Can't remember where I found them exactly but when I do I'll happily provide a link)
Rp @ 10ma = 17k3
Rp @ 20ma = 13k7
Rp @ 30ma = 12k
Rp @ 40ma = 10k9

Seems everyone uses the 25t/3c24 curves as even tube manuals from the day pretty much say that they are "close enough".

edit:
I was looking at the curves for the 25t/3c24...eimac wasn't going for ease of readablity when they made them were they?
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