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Old 14th April 2007, 08:50 PM   #31
Salas is offline Salas  Greece
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Quote:
Originally posted by Wavebourn


...and think of distortions added by more amplification needed to drive it...

Think of costs mainly, because good driver transformers are the answer, and lead to the purest sound...Or a pentode driver, they go balancing nicely having opposite tone.
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Old 14th April 2007, 09:17 PM   #32
Tweeker is offline Tweeker  United States
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Purest sound, and/or phase shifts that you cannot feedback around on top of the OPT. And the more gain needed caveat still applies, cmiller may be an issue with stepup.

The possibly sacrilegious answer is a (either FET or sweep tube) follower driven by a Western Electric 417A, 437A, EC8010, EC8020, triode-strapped E55L, D3a etc.
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Old 14th April 2007, 10:06 PM   #33
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Quote:
Originally posted by Tweeker

The possibly sacrilegious answer is a (either FET or sweep tube) follower driven by a Western Electric 417A, 437A, EC8010, EC8020, triode-strapped E55L, D3a etc.
It is exactly what I've found. 50L6GC triode strapped drives solid state voltage follower loaded by a voltage to current converter, like this one:

Click the image to open in full size.


For Hi-fi idle current equals to a half of maximal output current (maximal efficiency), for high end it equals to the maximal current (a voltage follower always sees the same emitter current: minimal possible distortions).
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Old 16th April 2007, 12:49 AM   #34
jarthel is offline jarthel  Australia
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I thought I was clear when I wrote the thread.

hopefully discussions can be restricted to power output tubes like el34, kt88, 6550, 300b, 845, 2a3 and etc.

like why use a 300b at all when el34 are much cheaper. does a 300b has a technical/sonic advantage?
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Old 16th April 2007, 01:45 AM   #35
Tweeker is offline Tweeker  United States
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If the 300Bs in question are really as good as Western Electric claims, then do do have some advantages over EL34s. I keep thinking about a pair in push pull at 100ma with an 11K anode to anode load.

Curves are at 350V anode, with fixed bias.
Curve 1: 30ma
Curve 2: 40ma
Curve 3: 60ma
Curve 4: 80ma
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File Type: jpg 300b grey distortion.jpg (97.3 KB, 856 views)
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Old 16th April 2007, 07:19 AM   #36
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Hi Tweeker,

Quote:
If the 300Bs in question are really as good as Western Electric claims, then do do have some advantages over EL34s.
Interesting half-sentence in front. Two weeks ago I was given some boutique 300B (considered to be somehow "improved" 300B) to trace, and after sending the plots back to the distributor, he very angrily called me by phone, forbade me to publish those and mention the brand by threatening for lawsuits because it would harm the business. "With your plots you have done enough harm on business already anyway", he shouted. Oh well, some folks just canīt stand the truth, especially when it will have impact on their wallet.

But usually a good real (non-boutique) 300B, WE or not, is considerable more linear than a triode strapped plain EL34, hands down, indeed. Usually.

For those who donīt believe, they should stop repeating legends and pointing at stone-age plots, but should apply my tag-line and see for themselves.

Regards,

Tom

EDIT: A similar effect can be found with modern KT88/6550. Patrick Turner (Australia) did some interesting measurements with these, showing how off modern copies are compared to old original datasheet plots. Funny enough, everbody makes SPICE models after those old plots and draws load lines on those old plots and then, using current production tubes, wonders what is wrong .....
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Old 16th April 2007, 09:01 AM   #37
Yvesm is offline Yvesm  France
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A similar effect . . . . occured some 30 years ago when tubes disapeared from new consumers products like TV set.

Large respected manufacturers stopped their tube factories and it was almost impossible to find decent replacement for maintenance.
The most sollicited tubes like horizontal sweep and VHF/UHF front end was **** and failed at incredible rate.
This forced the customer to replace its old TV set for a new one !

All (somewhat) aged maintenance technician (like me) could confirm that.

Business is business

Yves.
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Old 16th April 2007, 11:25 AM   #38
PCC88 is offline PCC88  United Kingdom
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The PX4 has similarities with a triode-strapped KT66.
Both are incredibly linear.
IMHO a triode-strapped KT66 could certainly be reagrded as a poor-man's PX4.
I believe this was the intention of MOV, to produce a valve that could replace the PX4.
And sonically, a PX4 wipes the floor with a 300b.
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Old 16th April 2007, 12:53 PM   #39
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I haven't heard them myself. But is the KT66 a poor man's PX4 because of any sonic difference or because of glamour, in this case lack thereof?

Any low-power DH triode "wipes the floor with a 300b." Usually that's because the 300B is harder to drive and needs a superior driver tube. "Nobody" can fail with a 45. (That doesn't sound right. But I guess it's true for the .45 as well.)
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Old 16th April 2007, 09:45 PM   #40
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Quote:
Originally posted by jarthel
I thought I was clear when I wrote the thread.

hopefully discussions can be restricted to power output tubes like el34, kt88, 6550, 300b, 845, 2a3 and etc.

like why use a 300b at all when el34 are much cheaper. does a 300b has a technical/sonic advantage?
Well it (the 300b or 845) should have a sonic advantage. All other things being equal, the el34 is closest, so far as I can tell others rave over the el84, (this assumes that you can approximately believe the tube curves) and your power out put reqiorements are not fierce

BUT the "problem" in general with DHT triodes is that the heater is in the signal path. So whatever the curves suggest thats the first practical problem to overcome. I'm doing a 300b amp now and this is no small problem. An indirectly heated EL34 looks beautiful just at the moment... Maybe one day I'll get both the el34 amp and the 300b amp working at the same time and then I'll know if its worth the bother.

phn, the KT66 is just lovely if the new tubes match the old ones for performance. But the KT** series are not the most efficient as triodes I believe? I know that the extra current they use can cause LF performance problems in the transformer though. Thats another reason the 300b (and el34) scores, usually low current with lots of voltage. IMHO not the best way, as it seems to negate a lot of that fantastic linearity.

Cheers

Andy
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