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EL509 (JJ) or PL519?
EL509 (JJ) or PL519?
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Old 12th December 2010, 09:39 AM   #21
Tubes4e4 is offline Tubes4e4  Germany
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Hi tubelab,

another point to consider is to use considerable g1 auto prebiasing when applying g2 drive, since it helps maintaining op point stability a lot. Especially with xL509, which has a bad tendence for thermic runaway when operated near its dissipation limits especially when g2 is severely loaded additionally by current takeover from the anode on low voltage anode swing (I learned this lesson when plotting several samples; it just emphasizes what you wrote in your previous article in this thread).

IIRC, TdP in his lecture even insisted on doing it by a cathode resistor autobiasing (for g1) to get the needed reliable regulation, or at least using mixed fix and auto bias. He went to some lengths talking about the rather large tolerances across NOS and new production xL509 types, even within the same production batch.

Regards, Tom
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Old 12th December 2010, 11:13 AM   #22
artosalo is offline artosalo  Finland
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Quote:
Driver stage weakness you say? Like?
I see that by replacing the CF-driver tube ECC82 to parallel connected 6N6P and biasing it to essentially higer standing current, most of the driving problems would be solved.

I have used 6N6P as a CF-driver with hi-mu connected GU50 which had the dynamic input resistance of some 300...330 ohms and the results were very good.

A Mosfet would do this job even better, but in my opinion, then we are not anymore involved in real tube amplifiers and I leave these constructions to other designers.
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Old 12th December 2010, 07:39 PM   #23
Miniwatt is offline Miniwatt  Netherlands
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I was thinking the same, what if I replace the ecc82 with a ecc99, that would probably be the first experiment after building it according to the schematic.
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Old 12th December 2010, 08:52 PM   #24
artosalo is offline artosalo  Finland
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ECC99 seems to be almost as good as 6N6P for this purpose.
I assume no problems.
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Old 12th December 2010, 09:56 PM   #25
Allen Wright is offline Allen Wright  Switzerland
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Quote:
Originally Posted by tubelab.com View Post
The JJ EL509 claims a 700 volt rating on the screen grid.
What JJ claim and what works in real life is FAR FAR away from each other.

Horrible tube in my opinion, they blow if the screens have more than 250V.

700V? BULLS**T.

Regards, Allen
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Old 12th December 2010, 10:18 PM   #26
Tubelab_com is offline Tubelab_com  United States
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Quote:
Horrible tube in my opinion, they blow if the screens have more than 250V.
I have heard that, but since I have no first hand experience I didn't want to say it.

So it seems that JJ just copied selected bits of an old data sheet without knowing what they were printing. The JJ may well be a copy of an old EL509 sweep tube. No sweep tube that I have ever met will work with 450+ volts on the screen in pentode mode. Some survive in triode. So, if this is true the JJ may work in screen drive mode. Again, the only way to know for sure is to try it.
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Old 12th December 2010, 10:36 PM   #27
Miniwatt is offline Miniwatt  Netherlands
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Okay, PL519 it is then

Cheers.
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Old 12th December 2010, 11:48 PM   #28
adam2a3 is offline adam2a3  Greece
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I have also built this amp for a friend, using Ei EL519 tubes. It has a very clean sound with amazing bass, giving more than 10 Watts/ch. But, if overdriven, strange things happen. Distortion does not sound like any SE triode amp, but appears suddenly, along with some cracking noises. (checked with ESL-57 Quad speakers).
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Old 13th December 2010, 10:42 AM   #29
Tubes4e4 is offline Tubes4e4  Germany
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Hi adam2a3,

Quote:
I have also built this amp (...)
Which one? The Bob D one or the Synola?

Tom
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Old 13th December 2010, 01:40 PM   #30
adam2a3 is offline adam2a3  Greece
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Hello Tom,
it is the Bob D amp I tried. If this power is ok with your speakers it is an excellent amp. Otherwise, at clipping you will not hear distorted music but distorted noises. The trim pot that affects all biasing must be a 10 turn pot otherwise it is difficult to adjust it.
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