Whole design history is under this thread:
http://www.diyaudio.com/forums/tubes-valves/178910-se-tesla-e34l.html
So the desing is just about one week old.
http://www.diyaudio.com/forums/tubes-valves/178910-se-tesla-e34l.html
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.
Regards
M. Gregg
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.
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.
Regards
M. Gregg
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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.
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
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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.
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
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
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If you think the core saturation can be a limiting factor in case of GXSE10-series transformer, then just use the bigger GXSE15-.
Then you have better performance expectation in this consideration.
Yes, I have seen this transformer test before. There the Edcor XSE-series transformer performed quite well. However, the GXSE-series should be one class higher if considered as a HIFI-transformer.
Please specify in detail what you mean.
Similar performance, a tad more power, and a simpler output transformer giving you more choice of transformers, and it's a very simple improvement that you can reverse if you don't like it.
Add to that it's the same idea as used in Quad 2's and many MacIntosh designs.
I do not see where the added power could come if the supply voltage and load impedance were the same. I rather see the circuit you suggested as an alternative to create local NFB and with that respect it works very well. I have also tested and used it in some of my prototypes.
It could be a good combination the have UL-connection and OPT's secondary connected in series with the cathode. I have not tested this.
Still I would have some amount of global feedback too.
I do not see your point. Simpler transformer ? In respect of what ?
I see that this only looks a bit same than QUAD/MacIntosh, but not really is similar. Below is the principle circuit of QUAD.
Here the primary load is distributed between anode and cathode.
In case the secondary only, not part of primary, is in series with the cathode, there will be some NFB-effect but not the "real" load distribution since the turns ratio between primary and secondary is such high that secondary do not cause any/ essential load.
It could be a good combination the have UL-connection and OPT's secondary connected in series with the cathode. I have not tested this.
Still I would have some amount of global feedback too.
I do not see your point. Simpler transformer ? In respect of what ?
I see that this only looks a bit same than QUAD/MacIntosh, but not really is similar. Below is the principle circuit of QUAD.
An externally hosted image should be here but it was not working when we last tested it.
Here the primary load is distributed between anode and cathode.
In case the secondary only, not part of primary, is in series with the cathode, there will be some NFB-effect but not the "real" load distribution since the turns ratio between primary and secondary is such high that secondary do not cause any/ essential load.
Hi Artosalo.
A tad more power because the screen isn't being modulated so a bit more voltage swing on the anode before the control grid goes positive.
A simpler output transformer because it's not ultralinear.
Same as Quad/Mac because the cathode effectively drives the secondary via the coupling cap, granted the turns ratio is not ideal but it's a real effect but on a slightly lower scale.
A tad more power because the screen isn't being modulated so a bit more voltage swing on the anode before the control grid goes positive.
A simpler output transformer because it's not ultralinear.
Same as Quad/Mac because the cathode effectively drives the secondary via the coupling cap, granted the turns ratio is not ideal but it's a real effect but on a slightly lower scale.
Curiosity got the better of me so i dug out a quad2 opt and measured it.
9 volts applied to the anode primary from CT to anode gave 1 volt on the cathode winding CT to cathode, 950 mV on the secondary winding when connected for 8 ohms and 1280 mV when connected for 15 ohms.
So the turns ratio for either the 8 or 15 ohm setup is nigh on perfect.
You could go one step further and connect the bias resistor to the secondary as well as the bypass cap and that really would be a copy of the distributed load setup.
I have actually built this arrangement and it works a treat.
9 volts applied to the anode primary from CT to anode gave 1 volt on the cathode winding CT to cathode, 950 mV on the secondary winding when connected for 8 ohms and 1280 mV when connected for 15 ohms.
So the turns ratio for either the 8 or 15 ohm setup is nigh on perfect.
You could go one step further and connect the bias resistor to the secondary as well as the bypass cap and that really would be a copy of the distributed load setup.
I have actually built this arrangement and it works a treat.
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