|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
184.6.93.253
In Reply to: RE: He was asking about commercial 300B amps posted by drlowmu on April 07, 2014 at 07:48:28
I just got an email about these EML45s, 300Bs, etc. from none other than Dennis "Tube Wrangler"..... the man himself. Pretty good discussion I say !! Hes something else, plenty smart !!
Here we are, verbatum :
The EML "45" is not really a "45"-- it is built more like the EML 2A3.
Think of it like a "EML 2A3" 45-- just like the JJ 2A3-40 is really a
"300B" 2A3-- (the plate is larger than the tube would normally use).
With the 2A3 we have 2.5 volt filaments and fewer turns on the grids,
compared to a 300B. (BOTH are why the 2A3 is markedly superior to any
300B-- an ordinary "45" falls in between the 300B and the superior EML
2A3, but the EML "45" is a superior tube, just like the EML 2A3 is. There
is actually no performance difference between these two EML types...
assuming either is placed into a circuit that is optimized for IT.
Sure, the "45" has more grid turns-- that makes it a higher-mu tube
(than a 2A3), and that's why the 45 runs at 5K output loading.
Remember-- the harder you load the output tube (up to a reasonable
point), the more IMMEDIATE the sound gets-- the more detailed, deep and
structured. WE LIKE THAT. You also get "more" power out, and more
measured "distortion".
What happens with easier loading? MUCH lower measured distortion AT FULL
POWER. Does this help sonically? Not really-- not ordinarily... because
ordinarily we ARE NOT running full power-- full power measurements, while
interesting, really have nothing to do with musical integrity..... what
we normally appreciate in music.
I tried an experiment with my amps a while back: normally, these are
driving the Great Plains "ALTEC" 604 Duplex into my MLTL enclosure. This
is using the 8 ohm tap on the Magnequest 2.5K output transformer, driving
the crossover network that drives both the woofer and the Mid-Tweeter.
In each channel I placed two amps in series, using both 16 ohm (using the
entire output windings) outputs. Each amp input was in parallel with the
other amp's input (common-drive configuration). Again, the outputs were
placed in SERIES, giving a 32 ohm output tap. This was loaded into the 8
ohm speaker.
I did this with both channels, using 4 amps total.
Well, what happened? It was just AWESOME--! Tons of super-clean,
wideband power. Everything was just plain better.
Why did this work so well? Well, it would not on an ordinary amp-- not
entirely-- it IS a mismatch. Distortion would obviously be higher. But
in the case of these amps, there is plenty of power available to both the
driver stage and the output tube. The power supplies simply drove the
overload cleanly, and the output tube simply accepted the load because it
could get all the current it needed.
It should be mentioned that the 2A3 output tube being run in this case
was operated at 44 ma. plate current at "normal" 2A3 plate voltage. Had
the tube been operated at the usual 60 ma., it would have rejected the
rather extreme mismatch.
All of my new Magnequests are of the ES-025 design as Mikey felt that
this would be rather nice. I agree!
---Dennis---
Follow Ups:
BTW 45's have LOWER mu than a 2A3, NOT higher as stated, and the reason they're loaded with 5K is that the Rp is double that of a 2A3, 1500 vs. 750 ohms.
Remember-- the harder you load the output tube (up to a reasonable
point), the more IMMEDIATE the sound gets-- the more detailed, deep and
structured. WE LIKE THAT. You also get "more" power out, and more
measured "distortion".
What happens with easier loading? MUCH lower measured distortion AT FULL
POWER. Does this help sonically? Not really-- not ordinarily... because
ordinarily we ARE NOT running full power-- full power measurements, while
interesting, really have nothing to do with musical integrity..... what
we normally appreciate in music.
Does Dennis Fraker have any recommendations for the correct harmonic profile for a SE DC 2A3 amp?
If I set up my FFT with a 1KHz sine wave input, what power output should I be measuring?
How far below the fundamental should each harmonic be in dB's?
This is for his 2.5K plate load recommendation at reduced bias current.
dt 667
Haven't you already demonstrated that lower distortion at full power ALSO EQUATES TO LOWER DISTORTION AT LOWER POWER ? ? ?
"Correct harmonic profile" ? ?? ? ? ? ? Would you believe me if I told you what it is ? I mean, if I made up some numbers and said, "this is it" ??
Considering the numbers of variables involved, is it at all realistic to even try for a specific "profile" ? ? ?
Based on your earlier experiments with a 7B4/12AX7, that you dismissed after measuring distortion and bandwidth issues, how is it that you still find reverence for the same source of this (proven) "less than ideal" advise ?
My question was probably too specific to get any direct answers.
Dennis always seemed to deal with rather esoteric concepts rather than schematics or measurements of any sort.
I never did test the SE 7B4 DC 2A3 circuit on the PC FFT, not yet.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: