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Old 17th January 2003, 03:54 PM   #21
dhaen is offline dhaen  Europe
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Quote:
Brett, John, or James? I'm still eagerly waiting a reply.
Joel,

If you are asking the question:
Why have more current drive than seems absolutely necessary?
Then my answer would have to be: slew rate, and the effects of non-linear input impedance, especially of DHT's.
Your designs may sound VERY good for the first watt. But what about loud passages, or transient response?

I refer you to Norman Crowhurst’s writings. They are available on my site.

Cheers,
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Old 17th January 2003, 04:06 PM   #22
Joel is offline Joel  United States
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Quote:
Originally posted by dhaen
Your designs may sound VERY good for the first watt. But what about loud passages, or transient response?
Well, since I only have .79 watts to play with...

But you've hit on my point exactly. How many people use all 8 watts of a 300-B? This is (yet another) case of designing for the fringes, when the listening experience day-to-day takes places very far from that territory. I'm told I must design my amp flat out to 200kHz, yet my only source material ends at 20kHz... where does it end?
A large DHT may have a better overload characteristic with large current drive - but who cares??? I don't run mine at clip, do you?
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Old 17th January 2003, 04:07 PM   #23
Joel is offline Joel  United States
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Quote:
Originally posted by dhaen
I refer you to Norman Crowhurst’s writings. They are available on my site.
Read all of them a couple years ago. They don't say anything about power triodes needing 40mA of driver current to sound good.
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Old 17th January 2003, 05:06 PM   #24
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Hi,

Quote:
But you've hit on my point exactly. How many people use all 8 watts of a 300-B?
OTOH,how many people run .79W amps and have, say 96 dB + efficiency speakersystems?

Seems there are always two sides to a coin.

The point is, it doesn't hurt to have some headroom and as John said it will improve slew rate and subjectively make the amp sound clearer and cleaner across the band.

To paint with a broad brush:

In my OTL amps I need to drive the combined Miller capacitance of 10 // dual 6080 triodes with a 12BH7A.
It works fine, but if I now replace all 6080s with 6336As I can assure you that the 12BH7A won't be able to swing it properly.

And yes,you can tell the highs are starting to roll off.

If you now look at the 845, 211 and other notoriously hard to drive big bottle tubes, you'll often see you almost need an amp to drive one.

Cheers,
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Old 17th January 2003, 05:54 PM   #25
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Default ...work in the way of important things...

Hi Joel,

I'm buried at work today and will be this evening too...

You raise an interesting point - For every rule of thumb or guide I know in designing amps, I also know of at least one exception that breaks it...

I will look at your choice of valves to see if I can find a reason why its so good with such a 'wimpy' driver...probably won't find one either!!! The fun is in the investigating

Bottom line...

If it sounds good to you - then its right - full stop!

more later

ciao
James
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Old 17th January 2003, 06:38 PM   #26
halojoy is offline halojoy  Sweden
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Thumbs up Thank God - he didn't mean me ....

Quote:
Originally posted by Joel
halojoy - what the hell are you talking about?
Wasn't you refering to me?

.. don't know a tube from a turkey baster

I guess I was reading your post ALL wrong.

Maybe I feel too inferior, when it comes to TUBES.
Sorry, Joel
------------------


/halo - mightn't be that bad after all
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Old 17th January 2003, 07:12 PM   #27
dhaen is offline dhaen  Europe
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Halojoy,

Quote:
Maybe I feel too inferior, when it comes to TUBES.
There's a cure: Join us!
Revoke your belief that SS is God's gift.
Can you really believe that everyone in this large "tube community" is wrong?
So there must be something in it...........
What to build as a demo?
Well, you build a simple SE amplifier, and see what it sounds like. It could be done with minimal funds: I presume you already have lots of electronic parts in stock.

Just DO IT And to take a quote from Bas Horneman's website:

http://home.zonnet.nl/horneman/

DIY SET is the easiest way..
to audio nirvana

Cheers,
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Old 17th January 2003, 07:23 PM   #28
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Default There's a cure: Join us!

Hi John,

Be ware of what you wish for.

Halojoy,

Join the magic and you'll be singing Bob Dylan songs all day long.

Look at Planet10,see how he does it...I'm sure he's feeling more confident every month and hey you know semi-conductors too.

Maybe you can teach us some useful applications for these too?

Not that I want to make hybrids,but you never know what's around the bend.

Cheers,
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Old 17th January 2003, 07:46 PM   #29
Joel is offline Joel  United States
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Quote:
DIY SET is the easiest way to audio nirvana
Yup.
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Old 17th January 2003, 08:38 PM   #30
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Quote:
Originally posted by Joel
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.
Yes! I've tried a few of the high current drivers for the 300B and while they were initially impressive they all suffered from upper midrange glare. I ended up preferring a wimpy little 6J7 at 2ma to all the high current pentodes drivers I tried.
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