Hi,
I have a single-ended project coming up, planning on using Electra-Print OPT and potentially IST.
I was hoping someone could comment on their experience on using their IST (SE:SE), my first time using IST in a design, would love to hear some testimonials 🙂
Thanks.
I have a single-ended project coming up, planning on using Electra-Print OPT and potentially IST.
I was hoping someone could comment on their experience on using their IST (SE:SE), my first time using IST in a design, would love to hear some testimonials 🙂
Thanks.
I have used the 1:1 single ended Electra-Print Interstage transformers.
I used an ECC99 to drive two of them, one triode per Interstage (Stereo).
The ECC99 triodes were individually self biased, and with individual bypass capacitors.
The two output tubes were 300B, with DC powered filaments, and two 3k output transformers.
I liked the sound of that amplifier.
Then I modified that amplifier, for the seminar I gave at VSAC 2008:
A comparison of 'parallel single ended' (one triode of an ECC99 driving one Electra-Print 1:1 to drive the parallel 300B tubes, and an SE output transformer with a primary of 1600 Ohms);
versus a push pull amplifier that used both ECC99 triodes that had a current sink in the parallel connected cathodes, (a combination splitter/driver), that drove a push pull 1:1 Electra-Print interstage, that drove two 300B in push pull, and a 6k plate to plate output transformer.
In low to medium amplitudes, the push pull amplifier was in class A operation, so the output tubes saw a combined plate load of 1500 Ohms, very close to the 1600 Ohms of the parallel single ended amplfier.
This was a simple listening test to try and hear the differences of SE versus PP, but with the same tubes, and similar plate loads, and both E-P interstage transformers.
I used an ECC99 to drive two of them, one triode per Interstage (Stereo).
The ECC99 triodes were individually self biased, and with individual bypass capacitors.
The two output tubes were 300B, with DC powered filaments, and two 3k output transformers.
I liked the sound of that amplifier.
Then I modified that amplifier, for the seminar I gave at VSAC 2008:
A comparison of 'parallel single ended' (one triode of an ECC99 driving one Electra-Print 1:1 to drive the parallel 300B tubes, and an SE output transformer with a primary of 1600 Ohms);
versus a push pull amplifier that used both ECC99 triodes that had a current sink in the parallel connected cathodes, (a combination splitter/driver), that drove a push pull 1:1 Electra-Print interstage, that drove two 300B in push pull, and a 6k plate to plate output transformer.
In low to medium amplitudes, the push pull amplifier was in class A operation, so the output tubes saw a combined plate load of 1500 Ohms, very close to the 1600 Ohms of the parallel single ended amplfier.
This was a simple listening test to try and hear the differences of SE versus PP, but with the same tubes, and similar plate loads, and both E-P interstage transformers.
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Fantastic, thanks 6A3. Electra-Print has a good reputation, will be my first time using transformers made by Jack, I've swapped emails with him for a while, it's been a long time coming. I wonder if his low IMD winding techniques can be incorporated into his ISTs, I'll have to ask.
An alternative would be the Lundahl LL1671 30mA, likely more have used them, I will see what information I can find.
It all depends on what your project specifically needs. Can you share what you want to do?
The problem with the LL1671 is that you need a pretty low source impedance in order to maintain both frequency and phase response on the low end. You would have to use tubes like a 5687, D3a, 6E5P and so on.
If you wanted to use the 1671 as a single ended to push pull transformer, you would be in a much worse predicament with only 10H to load the driver.
If you can deal with the low inductance of the 1671, then you should be fine.
The problem with the LL1671 is that you need a pretty low source impedance in order to maintain both frequency and phase response on the low end. You would have to use tubes like a 5687, D3a, 6E5P and so on.
If you wanted to use the 1671 as a single ended to push pull transformer, you would be in a much worse predicament with only 10H to load the driver.
If you can deal with the low inductance of the 1671, then you should be fine.
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The LL1671 is spec'd for my design and would work well with the planned source impedance, more curious how DIYers felt the Lundahl ISTs perform subjectively in circuits appropriate for them. Reviews seem to be mixed.
Thanks B, I will reach out to Dave and see what he has available. Glancing over his site, the DHT specific 1:1 nickel IST with the filament tap is interesting.
In my experience the lundahl transformers are very picky about how you load them. If you get it wrong, they are very unforgiving. If you get it right, then they sound pretty good.
I have not had experience with the LL1671, but I have had experience with the LL1660. I tried driving the 1660 with a 6J5 and ended up with some ringing and other issues.
The only other experience I have had with ISTs all come from vintage parts. My favorites being the old tango ISTs.
I have not had experience with the LL1671, but I have had experience with the LL1660. I tried driving the 1660 with a 6J5 and ended up with some ringing and other issues.
The only other experience I have had with ISTs all come from vintage parts. My favorites being the old tango ISTs.
mr ed,
The only written report I ever saw of my seminar is:
Vacuum Tube State of the Art Conference?VSAC 2008 Report By Jeff Poth
The first photo and caption below it is about my seminar.
The first part of the Seminar was the discussion of the similarity of parts, and quiescent operating voltages and currents of the PP and PSE 300B amplifiers.
All 300B tubes had 55mA each, and the same plate to filament voltage.
PP plates saw 6000 Ohms plate to plate/2 = 3000 Ohm plate load line per plate.
SE plates saw 1600 Ohms x 2 = 3200 Ohm plate load line per plate.
All tubes were individually self biased.
The ECC99 triodes all had the same plate current, and the same plate to cathode voltage.
Two ECC99 triodes with parallel cathodes and current sink, drove an Electra-Print 1:1 PP to PP interstage, that drove the PP 300B tubes.
One ECC99 triode, self biased, drove a 1:1 Bifilar Electra-Print Interstage, which drive two 300B in parallel SE.
The Seminar moved from the discussion room to the listening room.
The room was packed (*** more on this later).
There were only one PP mono-block and one Parallel SE mono-block 300B amplifier.
The signal source was the Left Channel of a CD player. Both Stereo recordings (again, Left Channel) and Mono (again, Left Channel) were sent to both PP and SE mono-blocks.
The mirror image Usher S-520 speakers faced each other 1 inch apart, and one speaker was connected in opposite phase. The two amplifiers were exactly amplitude matched by turning the gain of one, until there was a deep and complete Null of sound.
Then the out-of-phase speaker was re-connected in-phase; and the speakers were faced to the audience.
The Mono signal was switched back and forth from PP to PSE multiple times.
The Stereo Left channel signal was switched back and forth from PP to PSE multiple times.
But that meant that one speaker was the PP speaker, and one speaker was the PSE speaker.
Do you see the one flaw in this test? ***
Think of a person that has one or both ears that can only "see" one speaker, and the other speaker has a second person in the audience in front of the first persons ear(s).
Think of a person that only has one working ear. The two speakers are not at the same angle to the one ear (frequency rolloff for an indirectly aimed speaker, versus the other speaker that is directly pointed at the one working ear).
Or, a second person is between one speaker and the one working ear, but the other speaker is not shielded from the one working ear (it "sees" the other speaker).
I did not even think of or discover this problem ***, until I did the listening session.
I should not only have switched the CD Left Channel output between the PP and PSE amplifier inputs, I should have disconnected one speaker, and then switched the other speaker between the PP and PSE amplifier outputs. Then the sound would always be coming from one location (not from the two separate locations of the two speakers).
That would have taken care of the problem. ***
Well, live and learn.
By the way, for VSAC 2008, the rights to all the seminars, and meals, and live performances was very much of a bargain at $160 to access all that.
The lower registration $ fees did not give full access.
Long Live VSAC !
(too bad there will never be another VSAC).
The only written report I ever saw of my seminar is:
Vacuum Tube State of the Art Conference?VSAC 2008 Report By Jeff Poth
The first photo and caption below it is about my seminar.
The first part of the Seminar was the discussion of the similarity of parts, and quiescent operating voltages and currents of the PP and PSE 300B amplifiers.
All 300B tubes had 55mA each, and the same plate to filament voltage.
PP plates saw 6000 Ohms plate to plate/2 = 3000 Ohm plate load line per plate.
SE plates saw 1600 Ohms x 2 = 3200 Ohm plate load line per plate.
All tubes were individually self biased.
The ECC99 triodes all had the same plate current, and the same plate to cathode voltage.
Two ECC99 triodes with parallel cathodes and current sink, drove an Electra-Print 1:1 PP to PP interstage, that drove the PP 300B tubes.
One ECC99 triode, self biased, drove a 1:1 Bifilar Electra-Print Interstage, which drive two 300B in parallel SE.
The Seminar moved from the discussion room to the listening room.
The room was packed (*** more on this later).
There were only one PP mono-block and one Parallel SE mono-block 300B amplifier.
The signal source was the Left Channel of a CD player. Both Stereo recordings (again, Left Channel) and Mono (again, Left Channel) were sent to both PP and SE mono-blocks.
The mirror image Usher S-520 speakers faced each other 1 inch apart, and one speaker was connected in opposite phase. The two amplifiers were exactly amplitude matched by turning the gain of one, until there was a deep and complete Null of sound.
Then the out-of-phase speaker was re-connected in-phase; and the speakers were faced to the audience.
The Mono signal was switched back and forth from PP to PSE multiple times.
The Stereo Left channel signal was switched back and forth from PP to PSE multiple times.
But that meant that one speaker was the PP speaker, and one speaker was the PSE speaker.
Do you see the one flaw in this test? ***
Think of a person that has one or both ears that can only "see" one speaker, and the other speaker has a second person in the audience in front of the first persons ear(s).
Think of a person that only has one working ear. The two speakers are not at the same angle to the one ear (frequency rolloff for an indirectly aimed speaker, versus the other speaker that is directly pointed at the one working ear).
Or, a second person is between one speaker and the one working ear, but the other speaker is not shielded from the one working ear (it "sees" the other speaker).
I did not even think of or discover this problem ***, until I did the listening session.
I should not only have switched the CD Left Channel output between the PP and PSE amplifier inputs, I should have disconnected one speaker, and then switched the other speaker between the PP and PSE amplifier outputs. Then the sound would always be coming from one location (not from the two separate locations of the two speakers).
That would have taken care of the problem. ***
Well, live and learn.
By the way, for VSAC 2008, the rights to all the seminars, and meals, and live performances was very much of a bargain at $160 to access all that.
The lower registration $ fees did not give full access.
Long Live VSAC !
(too bad there will never be another VSAC).
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Hi euro21 - I had a great discussion with Dave and ordered a pair of his ISTs, thanks for your recommendation.