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Old 16th January 2003, 12:49 PM   #11
dhaen is offline dhaen  Europe
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Brett,
Quote:
when a factor of 5x the min theoretical drive current neccessary to slew the outputs is available in the driver, that's when the tubes really come alive
I have to agree.

Cheers,
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Old 16th January 2003, 01:08 PM   #12
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Default ...more power...

but in the driver stage!

I've not used DHTs until recently but I'm learning real fast that they like current drive...

I spent years getting ss amplifiers to sound as good as possible, and found out that getting the driver stage right was one of the big contributors to how they sounded. It seems that DHTs are the same.

I can relate to Paul Joppas remarks as with sand devices I ended up going for the same i.e. 5 times calculated current. Must be related to the detectable onset of slew rate limiting with complex music signals....

I really like the sound (!) of what you are doing! And the IT definitly sounds best to me too. If I was starting a 2A3 SE from scratch I would use an interstage or at least anode and grid chokes a la Thorsten... And I would probably choose a 6C45 to drive it but for a first amp. that's a bit hairy so the ECC99 is a great second choice...

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James D
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Old 16th January 2003, 01:12 PM   #13
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Default NEW 2A3

Hi,

Just for info:

A new 2A3 has been released by JJ (former Tesla) with a max. dissipation of 40W.

BTB

Sounds promising.


Cheers,
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Old 16th January 2003, 01:38 PM   #14
dhaen is offline dhaen  Europe
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Default 2A3 on steroids?

Mmmm, 2v heaters?....No hum from AC...
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Old 16th January 2003, 03:10 PM   #15
Joel is offline Joel  United States
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Brett, James, et al,

I have used a high mu driver (6F5) with a plate current of a puny 0.9mA to drive a 71-A, and granted, it may not be identical to a 2A3 or 300B in behavior, but....
do you have an explanation for why that amp sounded so clean, transparent, and dynamic? The same is true for my mono version, which uses an UX-201A with Ip of 3mA. Also, a "classic" like the WE91 uses a 6SJ7, etc, in all the updates I've seen - and that tube draws a few mA at best.
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Old 16th January 2003, 10:42 PM   #16
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Default ET ALL REPLIES...

Hi Joel,

Just some info:

Posted by Lynn Olson (M) of Aloha Audio on June 03, 2002 at 11:37:45
In Reply to: Confessions of a plate choke convert & a few CCS questions (long) posted by Doug Flynn on June 03, 2002 at 02:41:03:

One of the traps people fall into is not realizing just how low DHT distortion really is ... and that DHT's need a not only a lot of voltage, but enough current to overcome a substantial amount of capacitance (this controls slew rate).
How low? Well, the Amity has no trouble putting out 16 PP watts at 0.3% distortion, and 1.6 watts at 0.07%. That's *including* the distortion of a PP 7119 driver. If you really went nuts on the driver and used something like another 300B (!) as a driver, I'd bet the distortion might fall even more, maybe down to 0.2% or less.

300B's need anything from 42 to 60V rms of extremely linear drive to realize their full potential. I doubt that most people have even heard what a 300B really sounds like ... many DHT amps have more driver distortion than the final stage, and the drivers have the additional disadvantage of not delivering enough current to the DHT grid.

Although bare-bones engineering indicates that only a few milliamps are needed for full power at 20kHz, it's easy to forget that slew distortion is merely the current equivalent of voltage clipping ... and we all know distortion doesn't just go from zero to full. Instead, distortion gradually falls with decreasing level. The same thing happens with *current* distortion - the less current demanded, the more linear the driver is. Well, we can't do much about the current demand of the 300B grid, but we can certainly increase the current running through the driver ... by several times if transformer, choke, or active loading is employed.

Improving the slew rate by several times doesn't sound like what you'd expect. People expect shimmery triangles and amazing transients, but that's not what you notice. Instead, there is a dramatic reduction in the "electronic" coloration of the sound - in fact, most of the "tubey" vintage aspect of the sound disappears.

Since slew distortion is greatest at the zero crossing of the waveform, anything we can do to remove even the slightest trace of slew distortion (which is a different animal than generic THD) will give an astonishing improvement in hearing subtle details in complex passages. After all, we can all live with some distortion on the signal peaks, but we *don't* want any distortion at all in the zero-crossing region.

Personally, I think it's impossible to overdesign a driver or power supply. You want the most linearity possible with lots of linear current available, and the power supply needs to deliver lots of peak current while isolating the audio circuits from rectifier switch-noise and AC line noise.

If you're tired of vintage sound, improve the driver. Go nuts. Aim for 3 to 6dB of headroom or more, at least 15-20 mA of operating current, and transformer, choke, or active loading. (And yes, they all sound different!)

Cheers,
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Old 17th January 2003, 09:36 AM   #17
G is offline G  United States
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A 5687 will provide all of the current needs of a 2A3 and enough gain to do the job in one stage.

http://search.ebay.com/search/search...t&BasicSearch=
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Old 17th January 2003, 02:52 PM   #18
Joel is offline Joel  United States
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Frank, I can't verify if his facts are true or not at the moment, but I can tell you that I don't have "vintage", or "tubey" sound from any of my amps. In fact, I truly wonder what that is in the first place... it's bantered about alot by people who, 9 out of 10 times don't know a tube from a turkey baster. Usually they mean "warm"... which to me means rolled off highs and high distortion - symptoms of an old amp that hasn't been cared for for 50 years.

The cleanest amps I own, SS or tube, are my mono 71's. And they should sound the most "tubey" of all according to the gurus.

Brett, John, or James? I'm still eagerly waiting a reply.
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Old 17th January 2003, 03:13 PM   #19
halojoy is offline halojoy  Sweden
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Quote:
Originally posted by Joel
--------------------------
it's bantered about alot by people who, 9 out of 10 times don't know a tube from a turkey baster.
----------------------------------------
Say it clear out Joel
It is me halojoy, you mean
with:
don't know a tube from a turkey baster

I knew the TRUTH would come around - sooner or later

/halojoy - wants to go into hiding

(which would make some people jump for joy )
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Old 17th January 2003, 04:33 PM   #20
Joel is offline Joel  United States
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halojoy - what the hell are you talking about?
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