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EL84 datasheet max signal anode current

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Elerion

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Joined 2017
#1
Hi everyone.
I don't understand some of the values given for push-pull AB operation.
After somehour of simulation, and trying to find an answer in several books, I'm asking here, to see if anyone can help me out.

EL84 datasheet. Push pull AB.
Va = Vg2 = 300V
quiscent anode current = 2x36 mA
But, maximum signal anode current is given as just 2x46 mA

Is this last value in RMS or average or something? It seems to me like a very little increase. The simulations I've made show a much higher peak current. But its RMS value are very close,...

The other thing that looks strange is screen current.
Max signal screen current is stated as 2x7.5 mA for 250 Vg2, still push-pull.
But, looking into the curves, screen grid current is near 20 mA for Vg1 = 0 (250 Vg2).
7.5 mA occurs in the vecinity of -7 V. The signal input is surely reaching much more closer to Vg1 = 0.

Does anyone know how to interpret it?
Thank you.
 
#2
My interpretation of these datasheets would be that if you put an ammeter between B+ and the center tap of the output transformer, you would see 72mA at idle and 92mA with the applied signal (approximately of course).

Sometimes it's easy to gloss over AB1 vs. AB2 data sets on these data sheets as well.
 
#4
Good try, but no... There's only less than 5W of Class A Po out of 17W of maximum output. In any case, unless otherwise specified, the current shown in the datasheet means the average current, e.g., the maximum-signal plate current is 46mA per tube or 92mA for both tubes as audiowise showed above.
 
#6
Don't forgot to read the data sheet publish date, ie December 1956. Computers back then doesn't run SPICE. All measurement are done with real circuit and physical meters. The maximum screen current on that section is read from an "typical case" AB amplifier, with grid bias of about -7V.
 
#7
jazbo8 said:
Good try, but no... There's only less than 5W of Class A Po out of 17W of maximum output. In any case, unless otherwise specified, the current shown in the datasheet means the average current, e.g., the maximum-signal plate current is 46mA per tube or 92mA for both tubes as audiowise showed above.
Click to expand...

Yep, @ -14v in the AB table they might as well have just called it B.
 
#8
Then it is average current, not peak, as I suspected. In that case it fits very well with spice simulations. Thanks for the info.

I got the RCA receiving tube manual, but I didn't clearly read that (it's not a light and fast reading, though, I might have missed it).

I suppose there should be some manufacturer document or something explaining the terminology/abbreviations of the datasheets. Is there?
 
#9
Also be aware of the difference in biasing method. The book is showing in AB the cathode resistor of 130R and that gives the 36ma of quiescent current. No 0 sig. bias voltage. But in the Class B table you get 7ma with no sig. because it's fixed biased so near cutoff.
 
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#10
jazbo8 said:
Good try, but no... There's only less than 5W of Class A Po out of 17W of maximum output. In any case, unless otherwise specified, the current shown in the datasheet means the average current, e.g., the maximum-signal plate current is 46mA per tube or 92mA for both tubes as audiowise showed above.
Click to expand...

Something I'm not seeing in this example. The AB table gives 36ma plate current and 4ma screen @ 0v signal. That is the idle current. So if we use 40ma as the cathode current x 2 tubes through 130R cathode resistor we should see .08 x 130 = 10.4v on the cathode. How can we drive the grid to 14v signal without going into grid current, clipping?
 
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