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In Reply to: Low vs High Operating Points posted by danlaudionut on May 8, 2007 at 03:45:27:
Dan, you'll get all sorts of opinions but ultimately you know the drift, you'll have to make your own mind up. FWIW, I personally think that many differences of opinion arise simply because there really is no absolute rule that can be applied to every case.There’s no doubt that in most triodes generally higher current results in more linear operation. Also, higher voltages result in higher linear voltage swing, but this is not always required. Many factors need to be taken into account and a good starting point is always to plot the load line and set the operating points along the most linear portion of the line having regard to the required voltage swing.
However … when it comes to OP stages or any stage where a lower than optimal impedance load must be used then the previous stage becomes way more important and IMHO the pair of stages should be viewed as one and the operating points should be set according to the best overall result. For SETs, that generally means that lower operating current for the driver though less linear can often be used to offset the higher expected distortion of the OP stage due to opposite phase cancellation. This is both measurable and very audible IME. Since distortion in the OP stage is usually dominant higher current normally works better here as does higher load impedance. I also think that this is the reason that so many report such good results with (less linear) Pentode drivers for SETs.
Cheers,
Naz
Follow Ups:
NazI am thinking of the more relaxed vs
strained sound some declare at lower OPs.
I was thinking that may be the reason that I
prefer the KT88 over other tubes in my SE amp.
At 22W, the KT88 is just cruising while
the KT77/EL34/KT66 are near maxing out.
Since I seem to prefer that sound
and my next amp will be a 300B,
trying to bring what I know and
applying it to my next project.
So I guess I am asking what strains
the tube sonically more -
Dissipation or Voltage or Low Z OPT ?
How about a 300B at 450V/60mA/5K OPT?
To be specific.DanL
Dan,Since you asked: I've confirmed on Greg's 245 SEer that dissipation and high voltage both are culprits produing a "strained sound" in the SE output stage, and it effects the SE output trannie too !! A low Z trannie is less of a sonic problem IMHO.
See my prior posts by Dennis Fraker from Serious Stereo from 2006 on, re: 5/8ths throttle, etc., do a forum search. `
You may just wanna stay with the KT-88 Dan.
I'd personally optimize the amp's supply and lay out before more tubes were swapped. SEers are critical as to lay out and parts choices.
Jeff Medwin
JeffThis is for a completely different system.
My living room has the Monica 2, 12B4 Preamp
and the SE KT88 with Rythmic Plate subs
with a phono hopefully coming soon.
My kitchen has CAL Alpha/Delta CD sorce,
Marantz SR-66 and DIY Audax TL speakers with
Dynaudio D260 tweeters & GE 97F MR caps.
The Marantz was just given to me and
I have to say it has really good sound for a SS,
hey even some tube systems wouldn't compete.
Which brings me back to the 300B amp.
I am looking to replace/upgrade my Jolida 202
because it is noticeably the worst of the pack
and it is in my bedroom/primary listening room.
I have Acoustic Energy Threes in there - 8ohm/93dB
and Sonic Frontiers SFT-1HK and SFD-1MKII source.
It used to be the best system that I had.
BUT I guess things change 8^DDanL
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