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Any thoughts on this circuit?
Any thoughts on this circuit?
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Old 18th December 2010, 07:52 PM   #21
artosalo is offline artosalo  Finland
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Quote:
Keep it in pentode mode but include the secondary winding in the EL84 cathode ciruit
Why ?
Compared to UL, what are the benefits ?
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Old 18th December 2010, 09:57 PM   #22
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by artosalo View Post
Why ?
Compared to UL, what are the benefits ?
Do you have any history / info linked to the circuit you posted?


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M. Gregg
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Old 19th December 2010, 07:56 AM   #23
artosalo is offline artosalo  Finland
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Whole design history is under this thread:

SE TESLA E34L

So the desing is just about one week old.
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Old 19th December 2010, 09:23 AM   #24
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by artosalo View Post
Whole design history is under this thread:

SE TESLA E34L

So the desing is just about one week old.
Never saw it, it must have rolled onto the next page before I log on!

Have you tried the circuit yet?
Have you decided on the value of the O/P Tx it shows 5K on the drawing?
As you can see I will probably build it. LOL
Small distraction from my fun project.

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M. Gregg
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Old 19th December 2010, 10:05 AM   #25
artosalo is offline artosalo  Finland
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I have not built this circuit.
I just "designed" it using basic methods with data given by tube manufacturers. I have no doubt about it's functioning. Some fine tuning may be needed to cathode resistor of EL34 depending on the used supply voltage.

The output transformer impedance is 2,5 k, not 5k.
The type I prefer is Edcor GXSE10-8-2,5K.

It would be interesting to see somebody building this circuit and then see how it works.
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Old 19th December 2010, 10:41 AM   #26
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by artosalo View Post
I have not built this circuit.
I just "designed" it using basic methods with data given by tube manufacturers. I have no doubt about it's functioning. Some fine tuning may be needed to cathode resistor of EL34 depending on the used supply voltage.

The output transformer impedance is 2,5 k, not 5k.
The type I prefer is Edcor GXSE10-8-2,5K.

It would be interesting to see somebody building this circuit and then see how it works.
Sorry yes 2.5K I miss-read!
Thats interesting the circuit I posted shows a 5K load.
Wonder what the effect is reflected on the Anode loading. Obviously current is higher -that again is interesting the old circuits are usually warm sounding. higher currents should sound better.

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M. Gregg

Last edited by M Gregg; 19th December 2010 at 10:50 AM.
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Old 19th December 2010, 10:59 AM   #27
artosalo is offline artosalo  Finland
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The optimum anode load depends on the used supply voltage. This 2,5k should be good for 250 V. If the supply voltage were some 300 V, a bit higher anode load is optimum, say 3,5 k.

5k looks very higt to me.

Anyhow, this is a UL-circuit which makes it quite insensitive against load variation, just like triode connection.
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Old 19th December 2010, 08:11 PM   #28
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by artosalo View Post
The optimum anode load depends on the used supply voltage. This 2,5k should be good for 250 V. If the supply voltage were some 300 V, a bit higher anode load is optimum, say 3,5 k.

5k looks very higt to me.

Anyhow, this is a UL-circuit which makes it quite insensitive against load variation, just like triode connection.
Any thoughts.

If I use the GXSE15-8-2,5K would there be any gain in lower frequency clarity.

I am thinking in the physical size of the O/P Tx.

Regards
M. Gregg

Last edited by M Gregg; 19th December 2010 at 08:15 PM.
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Old 19th December 2010, 09:13 PM   #29
artosalo is offline artosalo  Finland
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Quote:
If I use the GXSE15-8-2,5K would there be any gain in lower frequency clarity.
I think the GXSE10-... does not suffer from too small power handling capacity at all (...for EL34 SE amp.). Typically transformers have some reserve, in this consideration. For example I have made tests with GU50 and 811A using GXSE10-size transformers and have had 15 watts output with low distortion at low frequencies.

One thing that surely affects to the performance at low frequencies is the inductance of the primary. Unfortunately Edcor does not publish this.

But an answer to your question: I do not know ? Both types should be tested before I could say anything sure.
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Old 19th December 2010, 09:22 PM   #30
M Gregg is offline M Gregg  England
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I was thinking that the core saturation at the low frequencies would be improved with the larger size of the laminations.

I guess you have no thoughts on the square wave effect?

Some interesting info in this thread, you have probably already seen it:
http://www.tubelab.com/BudgetOPT.htm


Regards
M. Gregg

Last edited by M Gregg; 19th December 2010 at 09:26 PM.
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