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In Reply to: RE: Elrog 300B posted by alexz on January 25, 2015 at 11:13:03
From the measured operating points (thank you alexz for the data!!) I calculated the plate resistance, using assumed values for mu of 3.00 for the Elrog and 3.85 for the others. The 3.00 value is calculated from the reported 3.5dB reduction in sensitivity, so that is somewhat questionable. I also assumed the mu was constant, which is not really true for any tube but 300Bs come about as close as any tube ever made.
I fully expected to see around 700 ohms for the WE and EML, with 900 or more for the Elrog. Here's what I got:
WE 1120 ohms
EML 907 ohms
Elrog 980 ohms
It's possible the WE is more worn than the others, but both the WE and EML are greater than I expected. I am not ready to draw any conclusions yet.
Follow Ups:
EML tubes comes with the measurments : Gm is 4.5 and 4.9. Obviously Rp is also vary, tubes have the same amplification.
HTH,
Alex
I calculate 4.24 for gm with the EML - pretty close after all!
Paul, i have one more thing for calculations .;-)
With output transformer 3.5k/16ohm with low output signal less the 1v, without load output is 0dB, with 16ohm load output goes down 2.6dB
That's 1221 ohms for rp plus the transformer resistive losses. Can you get transformer primary and secondary DC resistance? Usually secondary losses are similar to pirmary, so twice the primary DCR is an estimate. Subtract from 1221 to get another rp estimate.
From the manufacturer datasheet: primary DCR 93 ohm.
so, 1035 compared to 980 - wow, that's closer than I hoped for.
Great, actually not that far from EML.
Paul, you are absolutly correct, WE tubes are very much used in a last 15 years.
Also, I did some distortions measurements, in the same position with the same driver. ER300B measures best up to 2V/16ohm. At 1khz and 10khz ELrog is slightly better (1-2db) then EMlabs and 3-7dB better the WE (again, used)
Clipping is at 9v/16ohm (~5w)
Test bench: LAG-126 (analogue low THD) generator, HP333a distortion analyzer with o'scope connected after the bridge to see the spectrum.
One more, with ER300 sensitivity is down exactly 2/3. So driver tube is working harder (more distortions) with ER300, yet total level of distortions is down. Indeed remarkable tube !
that is matching the input and output stage well I see the same when I replace 6sn7 with 6GU7 in my KT120 triode connected amp. Lower total distwhen udeing 6gu7 with innherent higher dist
So the Elrog by your measurements has lower power and higher distortion than the EML I see. I wonder how that plays out sonically. I happily use the EML XLS in my SET. I'm very curious to hear the Elrog in my amplifier. Hopefully I will in the next few weeks. I'm energized by all the very positive reports so far. The EML has been excellent for me and will serve as my reference point.
Hi,
If you can accommodate about 3dB less amplification, about 5 watt power and if you 300B filaments PS are filtered DC, you will have a very pleasant surprise.
Thanks for the reply Alexz. My 300b SET is DC heated fortunately. I'm patiently waiting for a delayed shipment from Germany to the USA distributor. 5 watts should be no problem as I seldom get out of the 1st watt of power anyway.
..each tube make may have different optimal operating points,If you have bias adjustment you may adjust it a little..., The current drawn bye TJ mesh, EML , WE and Erog are quite different at the same Vg and Vpk. But in as selfbiased circuit the operating pint ar more similar. My simulations gives the following results for the typical 6sn7/6sn7/300b amp like Waltons schematic equal to "J.E. Labs 300B"
, YMMMV.
Edits: 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15 03/26/15 03/27/15 03/27/15
Enjoy !
Edits: 03/25/15
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