[corndog71]

It's funny to me how most guys look for tubes that are older yet as little used as possible not to mention random as far as how they measure. 


I read on another forum someone claimed that there's no way a hand-wound transformer could match a computer/machine wound transformer.

Thoughts?

[BobRex]

Hopefully Roger will add his thoughts.  Theory dictates that there shouldn't be a difference, and in fact, would side with the consistancy of the automated process.  But I think that those that have Roger's amps with his hand wound trannies, or LeFevre's trannies, or Slagle's, or .... would argue the opposite.  I've never done a side by side comparo, and I'm sure that most people haven't, now I'm curious.

[Freo-1]

I think that is too generic a claim to make.  I'm sure owners of Hashimoto hand wound silver transformers would beg to differ, just as a point of order. 

[Roger A. Modjeski]

All transformers are some combination of hand and machine wound. I doubt anyone holds a bobbin on one hand and wraps wire around it. There are many examples on YouTube, both good and bad.

As to computer winding: the computer in most winders simply controls the pitch of the wind and counts the turns. Tensioning is done on the spool de-reeler. There is a lot to setting up the winder, insulating the layers, bringing out the wires. When I wind I know what effects what because I designed the transformer. When I show someone else I can stress the important things, however it is a lot to learn. Why are some bakers, chefs and other artists better than others? Even if they show someone all they have done, the end result is rarely the same. 

One can wind very nice transformers with very simple home-made winders. I hope to offer transformer winding/construction as one of my classes here in Berkeley. There is no reason for not making your own transformers if you really want to. It's not rocket science, just something to learn from someone else who figured it out. It does take some effort to gather the materials, learn the design techniques. That part I would provide.

BTW, I have measured a Heyboer output transformer, sadly it was not so good. Edcor is inexpensive but not well thought of. Hammond may be better but I have not tested their wares. Winding with silver strikes me as silly for a few percent better conductivity and the fine wire primary is rarely silver as it is too soft to make thin wire. I know the Dynaco, Acrosound and many transformers made around the height of home building were very good. The guys making stuff these days have not done their homework. Besides  designing transformers I have developed a battery of bench tests to determine their performance before they go into an amp. Since the transformer is an important part of the feedback loop it's characteristics must be known separately.

[Freo-1]

All transformers are some combination of hand and machine wound. I doubt anyone holds a bobbin on one hand and wraps wire around it. There are many examples on YouTube, both good and bad.

As to computer winding: the computer in most winders simply controls the pitch of the wind and counts the turns. Tensioning is done on the spool de-reeler. There is a lot to setting up the winder, insulating the layers, bringing out the wires. When I wind I know what effects what because I designed the transformer. When I show someone else I can stress the important things, however it is a lot to learn. Why are some bakers, chefs and other artists better than others? Even if they show someone all they have done, the end result is rarely the same. 

One can wind very nice transformers with very simple home-made winders. I hope to offer transformer winding/construction as one of my classes here in Berkeley. There is no reason for not making your own transformers if you really want to. It's not rocket science, just something to learn from someone else who figured it out. It does take some effort to gather the materials, learn the design techniques. That part I would provide.

BTW, I have measured a Heyboer output transformer, sadly it was not so good. Edcor is inexpensive but not well thought of. Hammond may be better but I have not tested their wares. Winding with silver strikes me as silly for a few percent better conductivity and the fine wire primary is rarely silver as it is too soft to make thin wire. I know the Dynaco, Acrosound and many transformers made around the height of home building were very good. The guys making stuff these days have not done their homework. Besides  designing transformers I have developed a battery of bench tests to determine their performance before they go into an amp. Since the transformer is an important part of the feedback loop it's characteristics must be known separately.

Can you expand on what was not good about the Heyboer measurements?  I found the fit,finish,and sound from Heyboer better than Edcor.  If you measured a guitar type, then that would explain it.  They ask you if you want it for audio or guitar.   The output coupling transformers they made for the 6AH4 preamp are outstandding.

[bdp24]

It's funny to me how most guys look for tubes that are older yet as little used as possible not to mention random as far as how they measure. 


I read on another forum someone claimed that there's no way a hand-wound transformer could match a computer/machine wound transformer.

Thoughts?

Man did you ask the right guy. Testing tubes and making transformers, two of the things Roger is known as being an expert at.

[FullRangeMan]

It's funny to me how most guys look for tubes that are older yet as little used as possible not to mention random as far as how they measure. 


I read on another forum someone claimed that there's no way a hand-wound transformer could match a computer/machine wound transformer.

Thoughts?

This hand work vs machine wound is very well demonstrated in guitar pickups.
Today the most pickups are machine wound in Asia and the sound is different from the hand wound pickups, not bad or better, just different;

Musical instruments are tools that the musicians use according they need a specific sound timbre.
The vintage guitars from past have that sound part due the hand wound pickups, part due the old, very dry wood etc

[Roger A. Modjeski]

Can you expand on what was not good about the Heyboer measurements?  I found the fit,finish,and sound from Heyboer better than Edcor.  If you measured a guitar type, then that would explain it.  They ask you if you want it for audio or guitar.   The output coupling transformers they made for the 6AH4 preamp are outstandding.

I measured a push pull output transformer from Heyboer. It had very poor coupling from one half of the primary to the other. Your transformer is single ended, which poses other issues though not this one. Did you measure its response in your circuit?

There is so much to the designing and making of transformers I can only touch on a few things. I just got back from dinner where we talked about this for hours. I was with the person who gave me the Heyboer to test being told it was really great, of course the person who told him hadn't measured it.  If someone is serious about learning the art they should come here. I will likely give a class and we will make some. I would say its the thing that would most affect one's amplifier and the one thing most un-available to the public. If output transformers were are simple as capacitors to make then we would have a large selection, however they aren't.

[Freo-1]

Still not sure that the transformer you measured was made for guitar or audio?   Heyboer makes a lot of both types.  Would not expect one made of guitars to measure all that well (by design).  When oordering from them, one needs to specify the application.   I do know the output transformers on my 1625 amps sound better than the Edcor transformers I used for a previous 1625 project (they both sounded pretty good, but the Heyboer was a step up sonically). 

I know a lot of the DIY guys really like the Heyboer iron (especially compared to Hammond).  I seriously doubt they would get much business if they measured poorly for audio.  I think they are also a OEM supplier for audio tube amp manufactures.

[Roger A. Modjeski]

Still not sure that the transformer you measured was made for guitar or audio?   Heyboer makes a lot of both types.  Would not expect one made of guitars to measure all that well (by design).  When oordering from them, one needs to specify the application.   I do know the output transformers on my 1625 amps sound better than the Edcor transformers I used for a previous 1625 project (they both sounded pretty good, but the Heyboer was a step up sonically). 

I know a lot of the DIY guys really like the Heyboer iron (especially compared to Hammond).  I seriously doubt they would get much business if they measured poorly for audio.  I think they are also a OEM supplier for audio tube amp manufactures.

I seriously doubt the DIY guys have measured them. This one was for audio not guitar. When a transformer has this kind of problem the amount of feedback will be limited, the damping will thus be poor.  In my experience most DIYers dont measure their final amp, do they?

Have you come up with some performance specs you want to meet in the areas of frequency response, power bandwidth, damping and distortion?

[G Georgopoulos]

This one was for audio not guitar. When a transformer has this kind of problem the amount of feedback will be limited, the damping will thus be poor

I'm Not a tube expert,but yes alot of guitar transformers fall short of other transformers designed for hifi..

[Roger A. Modjeski]

They usually suffer in the bass since a guitar only goes down to 63 Hz. Also they don't have much high end as that is not needed. One only needs what one needs for the application. Guitar amps generally have little damping. This is not HI FI

This particular HI Fi transformer had good plate to plate response but suffered on the plate to CT on one side. This will cause feedback oscillation problems as the phase shift for the push and pull are not the same. If one doesn't use much feedback then there isn't a problem, however with a pentode amp and little feedback the damping will be poor. Pentode amps have very high output impedance.

[Freo-1]

I seriously doubt the DIY guys have measured them. This one was for audio not guitar. When a transformer has this kind of problem the amount of feedback will be limited, the damping will thus be poor.  In my experience most DIYers dont measure their final amp, do they?

Have you come up with some performance specs you want to meet in the areas of frequency response, power bandwidth, damping and distortion?

Good question.  Frequency response for preamps should be 20 Hz to 20KHz plus or minus 1 db.  The Thomas Meyer design 6AH4 preamp is an outstanding performer.  It is quieter and better sounding than just about any preamp I've ever heard.  The design is a winner.

For power amps, I think 30 to 15KHz flat, and 20 to 20KHz plus or minus 3 db is reasonable.  Under typical listening conditions. .02 distortion is reasonable, and .1 at moderate volume levels.  Honestly, the speakers normally will provide more distortion.  That is why I use ATC SCM-19 speakers with the Super Linear driver, along with powered subwoofers to get the best possible sound from the setup.  The 1625 power amps sound extremely clean and detailed, with excellent dynamics and 3D.  I am hoping to get similar results with the 6883B amps.  Damping is always low(er) for tube amps. 

[Roger A. Modjeski]

Good question.  Frequency response for preamps should be 20 Hz to 20KHz plus or minus 1 db.  The Thomas Meyer design 6AH4 preamp is an outstanding performer.  It is quieter and better sounding than just about any preamp I've ever heard.  The design is a winner.

For power amps, I think 30 to 15KHz flat, and 20 to 20KHz plus or minus 3 db is reasonable.  Under typical listening conditions. .02 distortion is reasonable, and .1 at moderate volume levels.  Honestly, the speakers normally will provide more distortion.  That is why I use ATC SCM-19 speakers with the Super Linear driver, along with powered subwoofers to get the best possible sound from the setup.  The 1625 power amps sound extremely clean and detailed, with excellent dynamics and 3D.  I am hoping to get similar results with the 6883B amps.  Damping is always low(er) for tube amps.

Thanks for stating some design goals. Some might disagree that plus/minus 3 dB is acceptable one of them being DNT Williamson (of that amplifier fame).  Distortion as low as 0.02% is hard to achieve without carefully applied feedback, just look at Atkinson's measurements of a significant sampling of tube amps. Speakers do have more distortion however they don't inter-modulate but amps do. Damping is a most overlooked issue and I strive for damping around 10 as more has little effect and less is not HI FI. If an amplifier has a damping factor much less than that (Atkinson has measured many around 3 to 5  and the Prima China was less than 1) it will provide a very non-flat signal to a speaker whose impedance varies.