The subject and opinions around OPTs can become endless. In the past 2 decades, I've bought and tested many SE OPTs, including Hammond, Edcor, James, Electraprint, Transcendar, Magnequest, Hashimoto and maybe one or two unknowns. Size does matter, but then again, going too small or too large can be detrimental to the overall performance, depending on what the design goals are.
For most SET designs I've done, they are usually using either the 45 or 2A3 DHTs... some others include the 3C24 and on the larger end, Western Electric 300b. Power output starts at ~2-watts with the 45, ~4-watts with the 2A3 and 3C24 and up to 10-watts with the 300b. My design goals are wide bandwidth, low distortion and high signal-to-noise ratio. In short, S/N is probably the most important specification, especially when you only have 2-watts of output power. As high efficiency speakers need to used, any residual output noise from the amplifier will be quite audible, which ruins everything. My 45 SETs are close to 90dB S/N referenced to 1-watt output. THD at 1-watt / 1KHz is less than 0.5% and bandwidth within 1dB is from 25Hz to 50KHz at 1-watt output. This is using the Hashimoto H507S. Going to their larger 20-watt OPT can be an improvement, but not by a huge margin. For me, I try and match the OPT to the desired specifications without getting too large or too small. Then again, YMMV.
Regards, KM
For most SET designs I've done, they are usually using either the 45 or 2A3 DHTs... some others include the 3C24 and on the larger end, Western Electric 300b. Power output starts at ~2-watts with the 45, ~4-watts with the 2A3 and 3C24 and up to 10-watts with the 300b. My design goals are wide bandwidth, low distortion and high signal-to-noise ratio. In short, S/N is probably the most important specification, especially when you only have 2-watts of output power. As high efficiency speakers need to used, any residual output noise from the amplifier will be quite audible, which ruins everything. My 45 SETs are close to 90dB S/N referenced to 1-watt output. THD at 1-watt / 1KHz is less than 0.5% and bandwidth within 1dB is from 25Hz to 50KHz at 1-watt output. This is using the Hashimoto H507S. Going to their larger 20-watt OPT can be an improvement, but not by a huge margin. For me, I try and match the OPT to the desired specifications without getting too large or too small. Then again, YMMV.
Regards, KM
"match the OPT to the desired specifications without getting too large or too small."
That's the point.
That's the point.
What they hear at the same loudness could be the result of their driver struggling to swing more voltage on 7k and on loud passages going into A2 grid current.
If I may add, I've used the H203U and H203S. The H203U may have better specs and look better on a scope. But driving real world speakers, the slight edge of the H203U (EI lams) in the bottom end is offset by a more vivid midrange and richer top end overtones from the smaller C-core H203S.
I chose the H203S over the H203U for my mono hifi which usually drives an Altec 756B + 32C/806 and don't find the bottom end lacking.
Here's a video (not for sonic evaluation) just to show the pairing. 😉
The understatement of the year. I wish more audiophiles and builders put videos online, you can evaluate from them, thanks. I sent a note to an amp builder who has a youtube channel to please put up some sound files of his/her amps. I got my head bitten off as though that was blasphemous, a Tascam handheld recording of a playback could tell you a lot more than talk.
Hashimoto released two new versions 203D & 507D, it would seem somehow redesigned to benefit two stage amplifiers. The paper specifications look the same. Wonder how they differ.
http://www.hashimoto-trans.co.jp/frame/tubecateng22.pdf
http://www.hashimoto-trans.co.jp/frame/tubecateng22.pdf
The difference is phase inversion... nothing more. The standard SE OPTs from Hashimoto are inverted phase, this results in the drive to the grid of the output tube (45, 2A3, 300b, etc.) as being in phase to the output winding. So, whatever circuitry you use to drive the output tube, it "should" not invert phase to the output tube driving the transformer.
As many SE designs are inverted phase to the output tube, this would result in an inverted output at the transformer. Hashimoto simply reversed the phase on these two OPTs for that reason. My 45 and 2A3 SE amps use a 5814a as a DC-coupled cascade circuit providing ~43 dB of gain which drives the 45/2A3 output tube with an in-phase signal. The overall result is an amplifier that's in phase. Hope this clarifies the difference.
Regards, KM
As many SE designs are inverted phase to the output tube, this would result in an inverted output at the transformer. Hashimoto simply reversed the phase on these two OPTs for that reason. My 45 and 2A3 SE amps use a 5814a as a DC-coupled cascade circuit providing ~43 dB of gain which drives the 45/2A3 output tube with an in-phase signal. The overall result is an amplifier that's in phase. Hope this clarifies the difference.
Regards, KM
From experience, one can invert the speaker connections at the secondary (even with grounding) with little to no harm to the frequency response of an OPT. An OPT has already a high step-down ratio, which translates to a low-potential secondary, so little to no parasitic capacitance increase will happen.
On the contrary, one cannot simply invert the connections of an interstage transformer.
On the contrary, one cannot simply invert the connections of an interstage transformer.
In general, I would agree that inverting the speaker connections in such a scenario would not be an issue. However, using Electrostatic speakers "could" present a problem if the negative of the speaker input is also grounded and at the same potential of the amplifier power ground via the grounded power connection. Granted, it's unlikely, but possible.
Still, Hashimoto apparently consider it a scenario worth addressing, albeit to date, only the smaller 7-watt OPTs have been made available with a non-inverting version. Perhaps they will make other versions available as same, but maybe waiting to see if the smaller ones sell first.
Regards, KM
Still, Hashimoto apparently consider it a scenario worth addressing, albeit to date, only the smaller 7-watt OPTs have been made available with a non-inverting version. Perhaps they will make other versions available as same, but maybe waiting to see if the smaller ones sell first.
Regards, KM
This 100%. And honestly this whole search for power at 20hz is IMHO not something I would focus on, there isn't much going on down there and most speakers aren't doing anything down there either, especially ones efficient enough to work with a 1.25W max amp.
Install some giant transformers on a flea watt amp and you will likely kill the liveliness in the midrange and top end. Trying for a build that doesn't even start rolling off until 20hz is probably gonna end up sounding dead everywhere else.
My suggestion would be to try the EI core Hashimoto HC-507U. I used a pair of these on a 47 amp using UL and it sounds really nice! I've also used the ISO FC12S but those won't have a 4 ohm tap if you need that.
I built a 47 amp using UL and shade feedback that sounds lovely.
I too have trod the search for the best sounding / performing output transformers over a ten year journey
ALL of these I have owned , NP Acoustics Amorphous Double C core ,Nogushi Finemet single C core small and larger versions , Hashimoto EI and C core , Tamura EI and C core , ISO C core , Electra - Print M19 , J&K custom double C core Permalloy 50 and pure Silver Wire and Sowter custom version of the 8983 with Mu Metal Nickel increased from %30 to %50 mixed with M6 %50 not pinstriped but all in the centre , the Nickel laminations are %78 content and now a Custom made Muse Coil Custom OTSE-060HY-046 this is multi tap and ultra linear tapes also .
The Muse Coil is currently on a SE UL 6550 performs splendidly but now will be shifted to the SE45 @ 4/6K load , chassis instead of the K&A 5K Double C core Silver .
All have their strengths and weaknesses but so far the go to is my Sowter 50/50 ( %78 pure nickel ) auto feed with ThermonicLab Plate Chokes - SRPP6SL7 bias 1.5mA absolute purity of human voice and end to end accuracy out performers the 5kg K&A pure silver winding double C core Nickel AKA Ongaku .
The Muse Coils are a masterpiece of workmanship and Alexander does custom winds so a 7K version of mine would be perfect as he gets bass down to 15Hz 1K driving impedance and HF upto 50Khz @ -1db and 25Hz @ Power output @68mA Idc @ 25Hz @ 1.65T-By current swing: 10,6W-By voltage swing: 7W .
After listened to all the exotic metals with SE2A3 and or 45's and the big four Japanese brands, Sowter custom wind Autoformers in parafeed outclasses them all IMHO 10Hz -50KHz -3dB @ 5 watts , K&A Silver close behind
Having said that HiB C cores come in just behind Nickel for me ISO then the larger Hashimoto's
Lets see where the Muse Coils slot in next !
Many images below and performance plots from Muse Coil.
Many Driver circuits were used including C3g triode strapped , SPRR 12AY7,5751, 12AT7 , 6SL7 , E280F and E180F triode strapped , 6SN7 and a few others over the past decade
So in conclusion IMHO if you need a 7K load flat to 20-25Hz then it will need to be custom wound maybe Muse Coils , but would suggest 25Hz is plenty low enough .
ALL of these I have owned , NP Acoustics Amorphous Double C core ,Nogushi Finemet single C core small and larger versions , Hashimoto EI and C core , Tamura EI and C core , ISO C core , Electra - Print M19 , J&K custom double C core Permalloy 50 and pure Silver Wire and Sowter custom version of the 8983 with Mu Metal Nickel increased from %30 to %50 mixed with M6 %50 not pinstriped but all in the centre , the Nickel laminations are %78 content and now a Custom made Muse Coil Custom OTSE-060HY-046 this is multi tap and ultra linear tapes also .
The Muse Coil is currently on a SE UL 6550 performs splendidly but now will be shifted to the SE45 @ 4/6K load , chassis instead of the K&A 5K Double C core Silver .
All have their strengths and weaknesses but so far the go to is my Sowter 50/50 ( %78 pure nickel ) auto feed with ThermonicLab Plate Chokes - SRPP6SL7 bias 1.5mA absolute purity of human voice and end to end accuracy out performers the 5kg K&A pure silver winding double C core Nickel AKA Ongaku .
The Muse Coils are a masterpiece of workmanship and Alexander does custom winds so a 7K version of mine would be perfect as he gets bass down to 15Hz 1K driving impedance and HF upto 50Khz @ -1db and 25Hz @ Power output @68mA Idc @ 25Hz @ 1.65T-By current swing: 10,6W-By voltage swing: 7W .
After listened to all the exotic metals with SE2A3 and or 45's and the big four Japanese brands, Sowter custom wind Autoformers in parafeed outclasses them all IMHO 10Hz -50KHz -3dB @ 5 watts , K&A Silver close behind
Having said that HiB C cores come in just behind Nickel for me ISO then the larger Hashimoto's
Lets see where the Muse Coils slot in next !
Many images below and performance plots from Muse Coil.
Many Driver circuits were used including C3g triode strapped , SPRR 12AY7,5751, 12AT7 , 6SL7 , E280F and E180F triode strapped , 6SN7 and a few others over the past decade
So in conclusion IMHO if you need a 7K load flat to 20-25Hz then it will need to be custom wound maybe Muse Coils , but would suggest 25Hz is plenty low enough .
Attachments
Last edited:
SE UL6550?
Forgot to mention Sony Tamradio/ Tamura Nickel 5K SE 84 / 5 watt EI core and Tamura 5K under test with SE UL6550
Off topic question, What’s the wire colors/windings for the Sony Tamradio output xformers? I bought 6 or 7 of the tube Sony R->R units to harvest the output xformers and holy basket speakers from. All the speaker drivers and output xformers on on the shelf but I’ve lost (or never took any) my notes.
Thanks in advance,
Rick
Forgot to mention Sony Tamradio/ Tamura Nickel 5K SE 84 / 5 watt EI core and Tamura 5K under test with SE UL6550
Off topic question, What’s the wire colors/windings for the Sony Tamradio output xformers? I bought 6 or 7 of the tube Sony R->R units to harvest the output xformers and holy basket speakers from. All the speaker drivers and output xformers on on the shelf but I’ve lost (or never took any) my notes.
Thanks in advance,
Rick
I have a few Plate Red / B+ Brown/ Secondary 8 ohms white / black and 600 ohms yellow/black
These are 3 primaries 2 secondaries no interleaving I tore a cooked one down
Sony's Tamura frequency bass response @ 1W with this OT is -1dB at 39Hz I saw measured on another forum
These are 3 primaries 2 secondaries no interleaving I tore a cooked one down
Sony's Tamura frequency bass response @ 1W with this OT is -1dB at 39Hz I saw measured on another forum
Attachments
Last edited:
Tamradio / Tamura is the amplifier in the pictures with EL84's x2 transformers exposed then with covers and the Tamura 5K under test with SE UL6550 refers to the picture included also in that post at the bottom with the Muse Coil transformers and 5K F915 Tamura next to them for testing later
The Muse Coils will be removed and used with a SE45 next