ygg-it,
If you can measure each half of the primary, you should be able to measure the whole complete primary. If you read about 8H, then the readings are probably reasonable.
As I said, 8H does not give very good low frequency response, especially when driven by a Pentode, it has high plate resistance, rp. Even if you use global negative feedback, it will distort at low frequencies.
And, your measurement of 2H 2H and 8H may only be correct when you use the inductance checker. It can be lower than that when you have the DC current from the output tube.
If you can measure each half of the primary, you should be able to measure the whole complete primary. If you read about 8H, then the readings are probably reasonable.
As I said, 8H does not give very good low frequency response, especially when driven by a Pentode, it has high plate resistance, rp. Even if you use global negative feedback, it will distort at low frequencies.
And, your measurement of 2H 2H and 8H may only be correct when you use the inductance checker. It can be lower than that when you have the DC current from the output tube.
Inbalance in a push-pull stage ( unequal plate current) will saturate the transformer core,
and this in turn will ruin LF properties.
and this in turn will ruin LF properties.
petertub,
Yes. Unbalanced DC current on push pull primary is a problem.
But . . . the amp with a LF problem is a Single Ended Amplifier.
Yes. Unbalanced DC current on push pull primary is a problem.
But . . . the amp with a LF problem is a Single Ended Amplifier.
Thanks Petertub, your post gave me chance to reconnect UL.
In the past I didn't like UL vs penthode, but I have made so many changes after that, so why do not test again UL?
So yesterday I did UL connection again: I have measured THD at 100Hz now at 0.4%, and 1KHz still at 0.2%.
THD at 60Hz is about 1% or less.
I still see 50Hz/100Hz power supply harmonics, and I think these made worse my measurements.
But what surpised me is the new bass sound now: less booming (which is negative for me), but faster and dynamic bass.
I've lost part of 3D image, bud 2D soundstage is more open now. I cannot tell you which of the two (penthode vs UL) I prefer...I need to test more, but for sure UL helped to reduce THD at low frequencies.
@6A3sUMMER: does UL reduce Plate resistance in SE EL34, than Pentode, so to reduce THD% at low frequency at accettable level? That should be a good trade off, taking my actual O.T.
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ygg-it,
Single Ended amps without global negative feedback:
(global negative feedback can partially correct the shortcomings/tradeoffs of the various operating modes, but can not fully do so, and not without tradeoffs).
Global negative feedback can be hard to adjust, and can cause instability.
EL34 plate resistance, rp, in Pentode mode is about 15k Ohms. Low damping factor, and hard to drive output transformer inductive reactance at low frequencies.
EL34 plate resistance, rp, in Ultra Linear mode (40%) is about 2500 Ohms
EL34 plate resistance, rp, in Triode Wired mode is about 1250 Ohms
1. The effective gain is highest in pentode mode, and lowest in triode wired mode, and in the middle in UL mode.
2. The damping factor is highest in triode wired mode, lowest in pentode mode, and in the middle in UL mode.
3. The power output is highest in pentode mode, lowest in triode wired mode, and in the middle in UL mode.
Part of how this all plays and affects the sound of your system is what loudspeakers you use (their impedance versus frequency, their efficiency, etc.).
I believe you may be able to see the results in your measurements, and you may be able to hear the different results in your system.
One of my SE amplifiers uses a KT66, and no global negative feedback. I have a switch that allows me to operate the amp in either UL mode, or Triode mode.
I Never change the position of that UL/Triode switch when the amp is powered. I power it off, and wait for the B+ bleeder resistors to discharge the filter capacitors, Only then will I move the UL/Triode switch, and then I power the amp on again.
The UL tap on that amp is 50%.
Single Ended amps without global negative feedback:
(global negative feedback can partially correct the shortcomings/tradeoffs of the various operating modes, but can not fully do so, and not without tradeoffs).
Global negative feedback can be hard to adjust, and can cause instability.
EL34 plate resistance, rp, in Pentode mode is about 15k Ohms. Low damping factor, and hard to drive output transformer inductive reactance at low frequencies.
EL34 plate resistance, rp, in Ultra Linear mode (40%) is about 2500 Ohms
EL34 plate resistance, rp, in Triode Wired mode is about 1250 Ohms
1. The effective gain is highest in pentode mode, and lowest in triode wired mode, and in the middle in UL mode.
2. The damping factor is highest in triode wired mode, lowest in pentode mode, and in the middle in UL mode.
3. The power output is highest in pentode mode, lowest in triode wired mode, and in the middle in UL mode.
Part of how this all plays and affects the sound of your system is what loudspeakers you use (their impedance versus frequency, their efficiency, etc.).
I believe you may be able to see the results in your measurements, and you may be able to hear the different results in your system.
One of my SE amplifiers uses a KT66, and no global negative feedback. I have a switch that allows me to operate the amp in either UL mode, or Triode mode.
I Never change the position of that UL/Triode switch when the amp is powered. I power it off, and wait for the B+ bleeder resistors to discharge the filter capacitors, Only then will I move the UL/Triode switch, and then I power the amp on again.
The UL tap on that amp is 50%.
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That doesn't really help the OP. Let's stay on topic rather than tossing in red herrings.
I am gree with 6A3
some point, just to add some info.
From Mullard data sheet of EL34 the Rp in pentode mode is 15 kohm and in triode mode is 910 ohm ohm.
All these data are verified on lab with a little changes due the brand and internal mechanic.
The connection in pentode mode , s.e., need 2 kohm of Zload with 250 vdc ( from data sheet) and you can get 11 watt with 10% of THD ( mainly 2nd harmonic).
For the triode connection you can use also the 2 kohm as load and the damping factor is much better than pentode connection, of course. The max power will be around 6 watt with 6-8% of THD.
These datas are similar for Telefunken and Philips ( owner of Mullard) and other brands.
In pentode mode the drive stage is easy due the gain .
In triode connection the gain is much lower, around 10 ( practical is bit less, measured in different brand), but it is simple to drive properly with a single stage.
So if your trafo has a low L at low frequency the use of triode connection is mandatory probably with no FB you can get a better performances.
In UL you are close to triode but much better than Pentode, considering your trafo.
Regarding the bass that is less booming in UL than pentode, it is normal due the Zout of the amp.
In Pentode mode the Zout is high so the freq. response with a real load attched follow the impedance of loudspeaker and you get more bass (more distortion also)
About the faster bass it comes from the low Zout of circuit so the damping factor is better (=lower Zout) and the control of woofer is better.
Walter
to Merlin
As you want. no problem, I have specified, just to be sure you understood what I wrote.
some point, just to add some info.
From Mullard data sheet of EL34 the Rp in pentode mode is 15 kohm and in triode mode is 910 ohm ohm.
All these data are verified on lab with a little changes due the brand and internal mechanic.
The connection in pentode mode , s.e., need 2 kohm of Zload with 250 vdc ( from data sheet) and you can get 11 watt with 10% of THD ( mainly 2nd harmonic).
For the triode connection you can use also the 2 kohm as load and the damping factor is much better than pentode connection, of course. The max power will be around 6 watt with 6-8% of THD.
These datas are similar for Telefunken and Philips ( owner of Mullard) and other brands.
In pentode mode the drive stage is easy due the gain .
In triode connection the gain is much lower, around 10 ( practical is bit less, measured in different brand), but it is simple to drive properly with a single stage.
So if your trafo has a low L at low frequency the use of triode connection is mandatory probably with no FB you can get a better performances.
In UL you are close to triode but much better than Pentode, considering your trafo.
Regarding the bass that is less booming in UL than pentode, it is normal due the Zout of the amp.
In Pentode mode the Zout is high so the freq. response with a real load attched follow the impedance of loudspeaker and you get more bass (more distortion also)
About the faster bass it comes from the low Zout of circuit so the damping factor is better (=lower Zout) and the control of woofer is better.
Walter
to Merlin
As you want. no problem, I have specified, just to be sure you understood what I wrote.