Great video on output transformer impedance - a complex topic. I prefer the measuring process in the direction in which the amp works, feeding the primary with AC and measuring the secondary voltage. There is a school of thought that the secondary needs to be loaded with a dummy resistor equalling the nominal resistance of the speaker. I tried both ways on a couple of OPT's, determining the voltage ratio with and without dummy load on the secondary and consequently the impedance ratio as the square of the voltage ratio, and I found that there is quite a big difference in the results. Then I decided to measure voltage and current on the primary of the OPT and calculate the impedance from this, with the load resistor on the secondary. Here, the impedance ratio turned out in one case nearly exactly the same as the value obtained by no-load voltage measurements, in the other case about 10% off, while the measurements of voltage ratio with dummy load was about 20% off. Conclusion - determining the impedance ratio through the no-load voltage ratio gives a valid result, while the voltage ratio with load on the secondary suggests significantly too high an impedance ratio.
Hey, I got that Donald Byrd "Royal Flush" LP and you were right, it's pretty awesome. It makes me imagine what it would have been like to hear them perform in a jazz club back then. Unfortunately Byrd has passed, but It's interesting that Herbie Hancock was only 21 back in 1962 and he's now 84, still married to the same girl and still performing. I'm now on the hunt for more Donald Byrd music.
Sweet! Cool to learn how to calculate turns ratio using an oscilloscope. I use a 6.3V or 24V transformer to determine voltage change ... dV between primary and secondary gives turns ratio.
Another easy way to measure output impedance is with a DE5000 meter. Attach a resistor or speaker to the output of know value to the secondary and the meter across the primary and it will measure the impedance to the milli ohm for that specific load.
G,day from Sydney Australia. Great tutorial, however would have liked to see the probe connections (over head camera). Learning outcomes. *Read specs of FC-205 data sheet *Associate your teaching with 5K and Hz range. * Visualize the sine wave phases on the scope (in and out) *Basic calcs ohms and crusibal horizontal and vertical lines. *Injection of low V via speaker input jacks. 🌏🇦🇺
Noted! I look forward to watching your improved version and am happy to link to to it! As published, it took me approximately 7 hours to setup, record, edit and publish this video and I'm sorry it didn't meet your standards for a free educational video. I don't own two cameras to record multiple different angles at the same time, and if i did, that would have added several more hours to the editing process for me. As I said, I look forward to watching and sharing your improved contribution to the hobby for everyone to learn from!
Hi Stephe, that was a great demo. I have a Tex. 2213 scope (a colleague gave me because he was too lazy to travel home with it) and a Philips PM5131 signal generator that was new old stock (if you like buttons, that thing is button galore). The little Chi-Fi OPT can be made to act like a 5K OPT for 8 Ohm speakers, but the question remains if the inductance is going to be enough for that impedance. Or you may loose too much low frequency response. It is already not very big. So perhaps it could be an idea to do a quick and dirty listening test with an amp you have at hand before you put in all the effort only to get Musical Paradise MP301 results.
This is true, I do have some other transformer if these don't work decent. I have a pair similar to these. www.tubesandmore.com/products/transformer-output-5w-5k-8k-primary-options-upgrade-fender-champ
Thanks for that, although I'm still a little uncertain of the phasing connection. Just to confirm, when we connect our feedback, we want an out of phase signal, so we connect the "negative" of the secondary to the feedback point? Or have I misunderstood?
It depends on how many inversions the amp design has. I honestly don't sweat it too much, (makes my brain hurt) if you get it backwards it's VERY obvious on initial testing lol.
@@mfr58 if you connect it incorrectly you’ll get positive feedback, think microphone pa feedback. In some cases positive feedback is needed. Like an oscillator in a radio.
I bought an assembled Chinese 6x5 + ECL82 tubes power supply board. It supposed to supply 260 v B+ but measured only 100+ v. After 2 weeks and many component swaps including the 2nd ECL82 tube, I figured it out that they put the zenor diode in the wrong direction.
Can you make another video showing how to measure the transformers PHASE? I still don't see the phase on the oscilloscope. Why would the primary and secondary be out of phase, for what reasons? most audio amplifiers want the primary and secondary to be In-Phase, but not sure what audio amplifier would want the primary and secondary to be 180 Out of phase or 270 degrees out of phase?
It depends on the amp design, how many signal inversions happen and if you are using global negative feedback. If you are using GNFB, you may have to invert the phase at the output transformer to have negative rather than positive feedback. Most of these were showing them in phase, but there were a couple of examples on the scope showing what 180 or inverted phase looks like. BTW not all amp have the input and the output in phase.
@@SkunkieDesignsElectronics So the only reason to reverse the phase on the primary is to get "positive feedback"? I'm not sure why anyone would want to use positive feedback because they would cause oscillations. Negative feedback reduces oscillations in the power amplifier section
@@SkunkieDesignsElectronics How can you measure if the Ultralinear TAP is 40% or 60% using the oscilloscope? I'm not sure what 40% or 60% means, 40% of what? and 60% of what?
They would reverse the polarity to NOT have positive feedback. Tube amps can have even or odd numbers of signal inversions depending on the design. Of course no one would intentionally hook up positive feedback.
I show this in the video, that one transformer has a 25 turns ration across the whole winding. From one end to the UL tap is 10 turns ratio, from the other end to the UL tap is 15 turns ratio. 10/25=0.4, the math is simple.
Great video on output transformer impedance - a complex topic. I prefer the measuring process in the direction in which the amp works, feeding the primary with AC and measuring the secondary voltage.
There is a school of thought that the secondary needs to be loaded with a dummy resistor equalling the nominal resistance of the speaker. I tried both ways on a couple of OPT's, determining the voltage ratio with and without dummy load on the secondary and consequently the impedance ratio as the square of the voltage ratio, and I found that there is quite a big difference in the results.
Then I decided to measure voltage and current on the primary of the OPT and calculate the impedance from this, with the load resistor on the secondary. Here, the impedance ratio turned out in one case nearly exactly the same as the value obtained by no-load voltage measurements, in the other case about 10% off, while the measurements of voltage ratio with dummy load was about 20% off.
Conclusion - determining the impedance ratio through the no-load voltage ratio gives a valid result, while the voltage ratio with load on the secondary suggests significantly too high an impedance ratio.
Good job on the tutorial on this, and glad the output was what you were hoping for.
And I have other options if this doesn't perform well :)
Great tutorial Steph! This is the method I have used for years and it has never let me down.
Hey, I got that Donald Byrd "Royal Flush" LP and you were right, it's pretty awesome. It makes me imagine what it would have been like to hear them perform in a jazz club back then. Unfortunately Byrd has passed, but It's interesting that Herbie Hancock was only 21 back in 1962 and he's now 84, still married to the same girl and still performing. I'm now on the hunt for more Donald Byrd music.
This is awesome for figuring out phasing and turns ratios on some old OT’s that were scrapped from other things. Thanks!
Sweet! Cool to learn how to calculate turns ratio using an oscilloscope. I use a 6.3V or 24V transformer to determine voltage change ... dV between primary and secondary gives turns ratio.
Hi, great video!Thank you very much.
Brilliantly described, thank you
Thank you for this video Stephe. You have clarified what I always fins, a difficult topic
You are so welcome!
Excellent video, thankyou!
Glad it was helpful!
Another easy way to measure output impedance is with a DE5000 meter. Attach a resistor or speaker to the output of know value to the secondary and the meter across the primary and it will measure the impedance to the milli ohm for that specific load.
G,day from Sydney Australia. Great tutorial, however would have liked to see the probe connections (over head camera).
Learning outcomes.
*Read specs of FC-205 data sheet
*Associate your teaching with 5K and Hz range.
* Visualize the sine wave phases on the scope (in and out)
*Basic calcs ohms and crusibal horizontal and vertical lines.
*Injection of low V via speaker input jacks.
🌏🇦🇺
Noted! I look forward to watching your improved version and am happy to link to to it!
As published, it took me approximately 7 hours to setup, record, edit and publish this video and I'm sorry it didn't meet your standards for a free educational video. I don't own two cameras to record multiple different angles at the same time, and if i did, that would have added several more hours to the editing process for me.
As I said, I look forward to watching and sharing your improved contribution to the hobby for everyone to learn from!
Hi Stephe, that was a great demo. I have a Tex. 2213 scope (a colleague gave me because he was too lazy to travel home with it) and a Philips PM5131 signal generator that was new old stock (if you like buttons, that thing is button galore). The little Chi-Fi OPT can be made to act like a 5K OPT for 8 Ohm speakers, but the question remains if the inductance is going to be enough for that impedance. Or you may loose too much low frequency response. It is already not very big. So perhaps it could be an idea to do a quick and dirty listening test with an amp you have at hand before you put in all the effort only to get Musical Paradise MP301 results.
This is true, I do have some other transformer if these don't work decent. I have a pair similar to these.
www.tubesandmore.com/products/transformer-output-5w-5k-8k-primary-options-upgrade-fender-champ
What OTs would you recommend for the A10, and what peak input voltage with your mods? Thanks.
No idea, on the voltage, been too long I can't remember.
Hi Stephe, Can this be done while the transformer is in the amp?
Yes, inject the signal into speaker jack and measure from the plate to B+ on SE or plate to plate on PP.
just like a guitar tube amp head needs to be paired with a good speaker cabinet .....to get the desired tone
Thanks for that, although I'm still a little uncertain of the phasing connection. Just to confirm, when we connect our feedback, we want an out of phase signal, so we connect the "negative" of the secondary to the feedback point? Or have I misunderstood?
It depends on how many inversions the amp design has. I honestly don't sweat it too much, (makes my brain hurt) if you get it backwards it's VERY obvious on initial testing lol.
@@mfr58 if you connect it incorrectly you’ll get positive feedback, think microphone pa feedback. In some cases positive feedback is needed. Like an oscillator in a radio.
@@davidedwards7172 Thanks
@@SkunkieDesignsElectronics Yes, I'll get some ear plugs.
Test with dummy loads!!!
I bought an assembled Chinese 6x5 + ECL82 tubes power supply board. It supposed to supply 260 v B+ but measured only 100+ v. After 2 weeks and many component swaps including the 2nd ECL82 tube, I figured it out that they put the zenor diode in the wrong direction.
That doesn't shock me, good job finding that!!!
Can you make another video showing how to measure the transformers PHASE? I still don't see the phase on the oscilloscope. Why would the primary and secondary be out of phase, for what reasons? most audio amplifiers want the primary and secondary to be In-Phase, but not sure what audio amplifier would want the primary and secondary to be 180 Out of phase or 270 degrees out of phase?
It depends on the amp design, how many signal inversions happen and if you are using global negative feedback. If you are using GNFB, you may have to invert the phase at the output transformer to have negative rather than positive feedback. Most of these were showing them in phase, but there were a couple of examples on the scope showing what 180 or inverted phase looks like. BTW not all amp have the input and the output in phase.
@@SkunkieDesignsElectronics So the only reason to reverse the phase on the primary is to get "positive feedback"? I'm not sure why anyone would want to use positive feedback because they would cause oscillations. Negative feedback reduces oscillations in the power amplifier section
@@SkunkieDesignsElectronics How can you measure if the Ultralinear TAP is 40% or 60% using the oscilloscope? I'm not sure what 40% or 60% means, 40% of what? and 60% of what?
They would reverse the polarity to NOT have positive feedback. Tube amps can have even or odd numbers of signal inversions depending on the design. Of course no one would intentionally hook up positive feedback.
I show this in the video, that one transformer has a 25 turns ration across the whole winding. From one end to the UL tap is 10 turns ratio, from the other end to the UL tap is 15 turns ratio. 10/25=0.4, the math is simple.