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In Reply to: RE: Small IDHT tube cathode bypassing posted by drlowmu on July 07, 2015 at 00:09:10
These terms are very revealing of your goals. That's perfectly OK, but many do not share those goals. And those goals are not attainable without introduction of "colorations" that most of us would like to avoid. (Coloration seems to be one of your goals, on the other hand.)
Anyway, you like to deride those who criticize your approach without having tried it. In this case, try using a Schottky or red LED and NO bypass capacitor, on the cathode to ground connection to bias a small signal triode. You might change your tune, or maybe changing your tune would constitute "sound shaping".
Follow Ups:
These terms are very revealing of your goals. That's perfectly OK, but many do not share those goals. And those goals are not attainable without introduction of "colorations" that most of us would like to avoid. (Coloration seems to be one of your goals, on the other hand.)
That is the conclusion I have arrived at as well. Although ultimate neutrality is not my primary goal, I'd still like to avoid gross colouration and maintain acceptable transparency, while achieving other goals.
Cheers,
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Both of you speak from NO listening experience with this technique, especially properly executed. Your lack of experience allows me to write off your "guesses and comments" as useless, which IMHO, they are.Sincerely,
Jeff Medwin
Edits: 07/09/15
Jeff, I deleted my previous response. I do not want to get caught in negative exchanges with you - they are miserable experiences that achieve nothing that justifies the effort.
As you know, I sought the type of experience you apparently demand. The reality is that you repeatedly mandated that experience be limited only to your Rx. Any expression of creative or independent thought - especially experimentation with other methods - has been vehemently discouraged. This behaviour has been repeated continually in our personal correspondence. Because of this, I requested that personal communication between us cease. I will endeavour to extended this agreement to public exchanges as well.
All the best to you Jeff,
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Jeff,
you like the sound of a dynamic volume expander and distortion. That is okay, and there is absolutely nothing wrong with creating a unique sound generating machine.
dynamic volume expander and high distortion I disagree with.
bandwidth limited yes.
There was a post by tube wrangler that claimed -1/2dB at 19KHz or something to that effect.
Perhaps the EML tubes and all his other special techniques allow for such performance from a SE 7B4 DC 2A3 circuit.
my point was that claims of high distortion are exxagerated.
Based on your ARTA graphs, the distortion of the SE 12AX7 DC 2A3 was NOT unusually high from what I remembered seeing.IMO, it looked OK.
Not sure how much your SE 2A3 circuit deviated from what DF or JM have done.
Edits: 07/13/15
since jeff's circuit is a moving target I'm probably off by a mile. :)
I'll take the high road on this, because there's no such thing as "winning" this argument. But for the record, I meant no criticism of your preferred approach; I merely recommended that you might try another that is diametrically different, just to hear the result for comparison.
With a Schottky biasing a wimpy triode such as a 12AX7 , it may work but the impedence will be far higher due to the low current through the diode . Y ou would also need far more diodes stacked to get the required bias . I seem to remember Naz proposed a solution using a star power LED for around 1mA or so (archives?) .
Al
But it does not negate the basic idea. I've never done it with a 12AX7 or with currents as low as 1mA. I got the idea originally from Naz.
91,
May I ask what output tube you plan to directly couple the 6C6 driver tube to? I to very much like the sound of the 6c6 pentode.
Thanks jet
My pleasure! IIRC, you had once posted some of your experiences with resistors on a similar amp on A'gon... Are you still running without a cathode bypass on the 6C6?I will be directly coupling the 6C6 to a 2A3 run at 42mA and 250V. Now, before people think that I am blindly following the Jeff and Dennis Rx:
> The operating point has been reported as sounding pretty decent by a few people.
> I think Emission Labs ~mu 4 tubes might sound really nice with a ~1:6 mA:V ratio. This is something that Thorsten recommends with 300Bs, but it might apply to 2A3s and maybe even EML 45s.
> I am loading the 2A3 with 4K2, not 2k5. I have two beautiful 5.9Kg custom nanocrystalline beasts sitting on my shelf...
> The cathode bypass will be sized for a ~8Hz -3dB point, not 20 - 25Hz (which could work well in the right amp, but I am not experimenting with that for this build).I will likely post the final build here, but would be happy to keep you updates as to my failures and successes as the build progresses.
Cheers,
91.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Edits: 07/10/15
I've got a fixed bias 2A3 on the bench at present . I have three pairs of 2A3 : RCA/Shuguang2A3C/Sovtek2A3 . All need more than 42mA to start singing , I use 48mA at present with 260V A-K with a 5k OPTX . May be worth bearing in mind once you've got it up and running to play with the op points a little
Al
.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
91, I am still running my 6C6 driver without the cathode bypass cap and I like the way it sounds but it provides a little less gain to the output tube. Please do keep me posted on your amplifier.
.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
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