Tweet
Originally posted by dchang0
View Post
Probably a typo by the original draftsman who might have been redrawing a pencilled original, or , say, a "1" sign was lost in photocopying (which would make it a WAY more reasonable 150V) or, as a last possibility, what an old meter could have read, although really those were much better than we think today.
I for one weaned on them, from late 60's to early 80's and even now and then, just for fun (it sure impresses customers
) even today. I even use my slide rule (a circular one to boot) which sure draws shop attendants crazy 
As the name implies, a 20k/V meter will show 20000*500 = 10M
input impedance on the 500V scale, which would be used there , WAY better than the typical 1M shown by most modern digital meters (now you know why now and then I still use the old analog ones) , only a few modern ones show 10M .Instead of guessing, reading the Runes or a just sacrificed goat liver, why not check the ... ugh ..... datasheet?
Such as: http://www.mif.pg.gda.pl/homepages/f...010/e/EF86.pdf
there on page 3 we read that for 220k plate load, 2k2 cathode resistor, supply voltage 300V , screen voltage derived from that, gain is some 200X and undistorted output voltage is 53V RMS ... completely impossible with just 50V on plate which practically must be saturation voltage (DC saturation, not signal clipping).
It certainly must have been quite higher, at least 100V or thereabouts, probably closer to 1/2 +V , simply for symmetry and max. undistorted peak to peak swing.
It is entirely possible that Dick Denney purposefully chose 50V right at the edge of the nonlinear region.
To boot, he "chose" nothing: values are pulled straight from datasheet!!!!!!
I guess you would do a service to (accurate) History by correcting once and forever that myth, repeated endlessly without checking.
By the way, VERY easy to check
, just build an EF86 stage with same part values, feed it proper voltage and measure For all the talk about modern Science, the Inquisition Vs. Galileo, the Flat Earth, yada yada yada, many are still rereading hundreds of times and endlessly arguing the old Sacred Texts while the Experiment is SO easy.
Oh well, won't hold my breath.
I'll put 50V as you report. If anyone else can shed light on the matter (especially with real-world measurements, although we know that wall voltages were lower in the 60s than now, and modern transformers are probably wound differently than the originals, etc.), please do.
And to be fair, JMI DID provide for a lot of primary taps to choose from
Comment