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Old 15th October 2008, 10:33 PM   #11
Elias is offline Elias  Finland
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Hello,

For normal music signal of course A2 operation would be very seldomly happening, because of music crest factor is usually between 10dB-20dB.

Maybe EL34 grid 1 can handle the occasional short peaks, maybe not. No data available, cannot tell.

On the other hand when the amplifier is driven to clipping then A2 is a 'normal' mode and maybe that's the end of that tube then.

So much guessing. Hmm.. I could sacrifice one EL34 on the altair of science for the purpose

- Elias
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Old 16th October 2008, 07:28 AM   #12
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Hello Elias,
In what load and B+ are you only getting 4W? If you are in the ballpark of 3k load and 3-400V B+, something is wrong! You should not need to go A2 until after doubling the 4W.

If you are using your surplus 230V:16V toroid (guess ca 18V unloaded) this represents below 1200:8ohms! If so, unwind until you have ca 12V unloaded.

Personally I do not believe in A2, that shouldn´t be needed with EL34, as it presents a signaldepending load to the driver after going past 0V Ug .
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Old 16th October 2008, 08:57 AM   #13
Elias is offline Elias  Finland
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Hello,

Quote:
Originally posted by revintage
In what load and B+ are you only getting 4W? If you are in the ballpark of 3k load and 3-400V B+, something is wrong! You should not need to go A2 until after doubling the 4W.

If you are using your surplus 230V:16V toroid (guess ca 18V unloaded) this represents below 1200:8ohms! If so, unwind until you have ca 12V unloaded.
EL34 is biased with CSS at kathode (LM317). I've tried currents between 50mA-80mA. B+ is 340V.

Yes I'm using the toroid as seen here
http://www.diyaudio.com/forums/showt...17#post1620017
I made an extra winding on top with several taps (between 4V-16V). The best seems to be 12V as you guess.

4W is the max power without grid 1 current

Maybe this russian EL34 has too low gm? I have only tested one sample of EL34.

- Elias
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Old 16th October 2008, 11:24 AM   #14
Merlinb is offline Merlinb  United Kingdom
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Quote:
Originally posted by Elias
EL34 is biased with CSS at kathode (LM317). I've tried currents between 50mA-80mA. B+ is 340V.

[/i]
Hang on, you mean a CCS under the cathode, in a single ended EL34? No wonder you're getting nothing out! How can you generate power in the OT if a 317 is trying to keep the current in it constant! You'll get almost no gain! I say ditch the CCS and use a zener, or something.
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Old 16th October 2008, 11:38 AM   #15
Elias is offline Elias  Finland
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Hello,

Quote:
Originally posted by Merlinb
Hang on, you mean a CCS under the cathode, in a single ended EL34? No wonder you're getting nothing out! How can you generate power in the OT if a 317 is trying to keep the current in it constant! You'll get almost no gain! I say ditch the CCS and use a zener, or something.
CCS is bypassed with big capacitor (470u).

- Elias
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Old 17th October 2008, 08:54 PM   #16
Elias is offline Elias  Finland
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Hello,

I did some more measurements and it seems that I can get 9 Wrms output power with a grid 1 peak current of 13 mApeak.

Without grid 1 current only 4W.

This is triode mode SE.

So it seems I can get more than 3dB improvement.

Should I be worried about 13mA peak?

In real life such a peak would be occuring very rarely taking into account the crest factor of music signal.

- Elias
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Old 17th October 2008, 09:27 PM   #17
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I was wrong about output power of teh triode-strapped EL34. According to the data sheet you should only get 6W(8%THD), 4W(6%THD) or 2,5W(5%THD) into 3k with B+ 370V and Iq 70mA. This is with 0ohm RDC in the OPT.
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Old 18th October 2008, 06:46 PM   #18
Elias is offline Elias  Finland
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Hello,

Quote:
Originally posted by revintage
According to the data sheet you should only get 6W(8%THD), 4W(6%THD) or 2,5W(5%THD) into 3k with B+ 370V and Iq 70mA. This is with 0ohm RDC in the OPT.
I measured from EL34 alone 2.3W 6%, 4W 8% and 6.3W 8%.

Datasheet forgot to mention you need to feed 4mA grid 1 current to get 6W At least in my case.

When using ECC83 as a driver, distortion improves 1-2% due to distortion cancellation. But with ECC83 max output is 4W, it cannot feed the grid current.

Feed back improves distortion even more of course, I quickly measured 3% with 4W.

There is 9W output possible with 13mA grid 1 current. Now I'm thinking if inserting FET interstage buffer is really worth of the +3dB power increase? With 20dB crest factor of music that seems as a small improvement.

- Elias
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