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Thread: JTM 45 build 400v plate voltage, how to calculate OT primary impedance?

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    JTM 45 build 400v plate voltage, how to calculate OT primary impedance?

    Hi All,
    I asked a similar question before, the suggestion was to learn the graphical technique. I have Merlin's book, but not sure what Im looking for (what part of the graph). The Amp should have around 400v plate voltage, with KT66 tubes. The output transformer has 9k, 8k and 6.6K primary taps.
    What part of the graph would tell me the target OT primary impedance?
    Thanks!
    Mike

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    I don't have Merlin's book but I guess it explains graphical loadline construction in PP amps. The primary impedance (Raa, Zaa) corresponds to 4 times the inverse slope of the optimal loadline.
    A quick check shows that the 6.6k tap should be closest. Higher Raa will reduce output power and increase screen losses.

    This old OSRAM datasheet gives some examples:
    https://drtube.com/datasheets/kt66-osram.pdf
    You want to look for the fixed bias configuration.

    This said, original JTM45 with Drake OTs used 8K. The earlier RS OTs had 6.6K and 8k taps.

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    Thanks Helmholtz, yes its the graphical load line technique. 6.6k, thanks! I tried picking through the data sheet but a common problem I have is finding definitions for the symbols.

    Also, thanks for the link as well..

    Is the switch to 6.6K and 8K something to do with switching to EL34? I read someplace that the early JTM45's had Radiospheres OT and KT66, then they switched transformers and output tubes as well.

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    Better Tone thru Mathematics bob p's Avatar
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    Maybe Steve Bench's tube pages will help.

    Part 3 - Of Loadlines, Power Output, and Distortion

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    "Stand back, I'm holding a calculator." - chinrest

    "I happen to have an original 1955 Stratocaster! The neck and body have been replaced with top quality Warmoth parts, I upgraded the hardware and put in custom, hand wound pickups. It's fabulous. There's nothing like that vintage tone or owning an original." - Chuck H

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    Thanks for the link, Bob. Reading ...

    Another question, probably should have asked before: The graphical techniques draw lines on a graph that already has the tubes characteristic family curves drawn. Where can we get good quality images with these curves? I checked the data sheets and they usually don't have graphs as detailed as the ones in the example, like the "Part 3" web page.

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    Is the switch to 6.6K and 8K something to do with switching to EL34?
    No, all the 50W EL34 versions came after the KT66 versions and used Drake OTs (types 784-128 and 784-139) with Raa of 3.2K, which is just fine and provides max. output power with EL34s.

    I read someplace that the early JTM45's had Radiospheres OT and KT66, then they switched transformers and output tubes as well.
    The early RadioSpares (RS) was a multi-tap general purpose (DIY) OT. There is some good information in Michael Doyle's book "The History of Marshall". The KT66 datasheet recommends Raa=8K for cathode bias operation only. I have no idea why Marshall used 8K with fixed bias and actually don't know if the Radiospares OTs were wired for 6.6k or 8k. Undistorted (THD=10%) output power of originals with 8k was around 30W or lower depending on actual voltages and KT66 quality.

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    Thanks Helmboltz. I just found some photos of a couple of originals, wow, what a build those things were with that big hole hacked in the chassis and all of those taps so close together on that little board. I read someplace that they had arcing problems since the tap connectors were so close together.

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    Having worked on a number of original JTM45 amps with the RS OT over the years...
    I would say 70% of them are wired for 6.6K whille the rest wired for 8K ....
    These amps were not monkeyed with.... they had the original solder marks and dye from the factory.
    Yes arcing was an issue with the pins and TAG board material...had to repair a number of them...
    Original JTM45 amps when given the proper mains voltage...and biased the KT66 tubes to like 40mA each with a GZ34 typically makes 450V on the plates..
    "Optimum Plate Load" is not always what guitar players like to hear....that "optimum" non-sense works best when designing transformers for Hi Fidelity equipment..
    "Optimum" meaning best bang for the buck..essentially you look at your Power Output curve vs Plate Load then you compare it to the Distortion output vs Plate load curve... Between these two curves you get a intersection or best compromise of most output for the least distortion....
    Regardless of the actual value of the Plate Load, the full distorted power output will always be the same...because you have a square wave ideally at 50% Duty Cycle hitting the rail voltage...
    Increasing the plate load above optimum with these type of Beam Tetrodes and Pentodes will result in less clean headroom.. ie the point at which the sine wave starts to clip will come in sooner...Some players love that others hate it...
    After 35 years of curve tracing and writing software to develop complex models, One thing I can pass on is to not waste time doing the full characteristic load-lines...they are an academic exercise and pure wast of time....
    The reason is the load is never really linear and the load-line is reactive which makes modeling the load-line more involved......tubes, even NOS tubes are all over the place in their parameters...and then there's FEEDBACK to help linearize the situation that also needs to be accounted for in the transfer function....
    Keep in mind that when drawing up a load line you need your reference plate voltage...most textbooks use the idle voltage which makes for errors... You need to use the B+ you would have when the amp is making maximum clean output signal...
    Since the B+ sags in many of these amp....if not then the load-line will be off by as much as 50 Volts or more... and your calculated power output will be much higher than reality...

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    Last edited by cerrem; 05-31-2018 at 03:30 PM.

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    Quote Originally Posted by cerrem View Post
    Having worked on a number of original JTM45 amps with the RS OT over the years...
    I would say 70% of them are wired for 6.6K whille the rest wired for 8K ....
    These amps were not monkeyed with.... they had the original solder marks and dye from the factory.
    Yes arcing was an issue with the pins and TAG board material...had to repair a number of them...
    Original JTM45 amps when given the proper mains voltage...and biased the KT66 tubes to like 40mA each with a GZ34 typically makes 450V on the plates..
    "Optimum Plate Load" is not always what guitar players like to hear....that "optimum" non-sense works best when designing transformers for Hi Fidelity equipment..
    "Optimum" meaning best bang for the buck..essentially you look at your Power Output curve vs Plate Load then you compare it to the Distortion output vs Plate load curve... Between these two curves you get a intersection or best compromise of most output for the least distortion....
    Regardless of the actual value of the Plate Load, the full distorted power output will always be the same...because you have a square wave ideally at 50% Duty Cycle hitting the rail voltage...
    Increasing the plate load above optimum with these type of Beam Tetrodes and Pentodes will result in less clean headroom.. ie the point at which the sine wave starts to clip will come in sooner...Some players love that others hate it...
    After 35 years of curve tracing and writing software to develop complex models, One thing I can pass on is to not waste time doing the full characteristic load-lines...they are an academic exercise and pure wast of time....
    The reason is the load is never really linear and the load-line is reactive which makes modeling the load-line more involved......tubes, even NOS tubes are all over the place in their parameters...and then there's FEEDBACK to help linearize the situation that also needs to be accounted for in the transfer function....
    Keep in mind that when drawing up a load line you need your reference plate voltage...most textbooks use the idle voltage which makes for errors... You need to use the B+ you would have when the amp is making maximum clean output signal...
    Since the B+ sags in many of these amp....if not then the load-line will be off by as much as 50 Volts or more... and your calculated power output will be much higher than reality...
    Cool, thanks cerrem! Re 6.6k vs 8k, are the differences for different output tube types, or are these all KT66? What would the effect be if you ran the amp, switched to 8k, then ran again, just in volume, or tone character as well?

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    Quote Originally Posted by mikepukmel View Post
    Cool, thanks cerrem! Re 6.6k vs 8k, are the differences for different output tube types, or are these all KT66? What would the effect be if you ran the amp, switched to 8k, then ran again, just in volume, or tone character as well?
    The 6.6K was intended for Ultra-Linear operation using the 43% taps.....that is a "classic" optimum value.....used for 6L6, KT66 and 5881 807 family of tubes...
    I believe the 8K is a "classic" value used for TRIODE connected 6L6 family of tubes...
    8K is also "classic" value for pair of EL84 or pair of 6V6 tubes in pentode wiring...
    Of course set plate loads need to be at specific operating voltage in order to properly operate...
    As for the 6.6K vs 8K ....6.6K is cleaner and punchier and 8K is like AC/DC Highway to hell sound..

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    Quote Originally Posted by cerrem View Post
    As for the 6.6K vs 8K ....6.6K is cleaner and punchier and 8K is like AC/DC Highway to hell sound..
    That’s interesting - the closest I’ve heard to that tone is the mid 70s 50w Marshall’s with the lower B+. I’ve had a couple of Lead & Bass combos with that tone, but I believe that some heads were like that too.

    Will certainly have to try an 8k OT with a JTM45 preamp some time. Did they have around 450v B+ too???

    Cheers

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    Quote Originally Posted by cerrem View Post
    The 6.6K was intended for Ultra-Linear operation using the 43% taps.....that is a "classic" optimum value.....used for 6L6, KT66 and 5881 807 family of tubes...
    I believe the 8K is a "classic" value used for TRIODE connected 6L6 family of tubes...
    8K is also "classic" value for pair of EL84 or pair of 6V6 tubes in pentode wiring...
    Of course set plate loads need to be at specific operating voltage in order to properly operate...
    As for the 6.6K vs 8K ....6.6K is cleaner and punchier and 8K is like AC/DC Highway to hell sound..
    Awesome, thanks for the info. Do you know of any amps that have a switch, even if inside, like with jumpers, or do you expect to wire the amp, set the bias and leave it?

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    Quote Originally Posted by mikepukmel View Post
    Awesome, thanks for the info. Do you know of any amps that have a switch, even if inside, like with jumpers, or do you expect to wire the amp, set the bias and leave it?
    Nowadays, I tend to dial an amp in and then just leave it the hell alone and focus more on playing music with the band...
    Switches on OT's can lead to arcing and extra parasitic inductance that can spell trouble...
    I learned my lesson back when I was young and eager to constantly modify amps...One night back in the 80's I was playing a show with a Marshall Major upside down and open chassis on top my 4x12 cab... I would solder different parts in and out between songs experimenting... Well I must have had way too many beers and whiskey shots and I forgot which way the STAND-BY switch is suppose to be when the amp is upside down... Well last thing I remember I was reaching to change out something in the Phase Inverter and WAMO !!! got thrown like 8 feet and on my back ...with my Les Paul still hanging around my neck.. Big blue spark with smoke..My band-mates yelled at me to stop clowning around and get up and start the next song..somehow I got up and everything was OK..
    So sometimes it's best to just leave amp be and play some music...
    And yes JTM45's made 450V when everything was all lined up...

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    Ouch!!!!!
    Alcohol and High Voltage donīt mix, period.
    Same as in my Shooting Club: they DO have a bar on the premises, and there is a door from the shooting area leading to it, it is a revolving door type : you can cross it one way but not go back, only exit is outsiden to the street, so you go home.
    And they have a BIG sign: Alcohol and Gunpowder do not mix.

    Back to the amps, I would not worry about the 400V vs. 450V "problem", and it definitely does not need or warrant changing OT impedance just for a little "optimization".

    If standard OTs are meant for 450V supply amps, and you build a 400V one ... just leave it , amp will sound exactly the same as before , it will just put out a little less power than before, no big deal.

    We are talking a meager 10/12% variation!!!!

    As said above, there is way more tube to tube variation than that.

    No need to be messing with (printed) tube curves for such a small difference, specially because you have no guarantee your tubes follow them at all.

    In fact I suspect modern tube makers just copy old datasheets so people think modern tubes are same as old ones ... I very much doubt that.

    If anything, and it worries you, get an "universal" OT like the original RS one (MM will love your cash input) or one ofn the Hammond ones or if you are really committed, a Turner Australia one , try different loads with *your* Tubes and pick the best by ear.

    If you are really comitted to experimenting, these Turner Audio transformers are the real deal: primaries split in 10 sections, secondaries split in 9 , all fully interleaved, by series-parallel combining sections on each side you can get a mind boggling set of combinations, such as anything from 560 ohm to 8k , all in the same OT.
    Basically he winds one layer and brings its ends out, so , say, 12 layers=12 separate windings, which you mix and match as you wish. Mind boggling possibilities and the Experimenterīs dream.
    I bet there is at least one model which you buy with a 100W core and allows you to build practically any Guitar Amp ever sold, go figure.
    for-sale-2-output-transformers



    Funny thing is, he gives all winding parameters in the descriptions, so these transformers can be cloned by a local winder .... I probably will build one or 2, a project for long cold boring Winters or endless raining seasons.

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    Quote Originally Posted by J M Fahey View Post
    Ouch!!!!!
    Alcohol and High Voltage donīt mix, period.
    Same as in my Shooting Club: they DO have a bar on the premises, and there is a door from the shooting area leading to it, it is a revolving door type : you can cross it one way but not go back, only exit is outsiden to the street, so you go home.
    And they have a BIG sign: Alcohol and Gunpowder do not mix.

    Back to the amps, I would not worry about the 400V vs. 450V "problem", and it definitely does not need or warrant changing OT impedance just for a little "optimization".

    If standard OTs are meant for 450V supply amps, and you build a 400V one ... just leave it , amp will sound exactly the same as before , it will just put out a little less power than before, no big deal.

    We are talking a meager 10/12% variation!!!!

    As said above, there is way more tube to tube variation than that.

    No need to be messing with (printed) tube curves for such a small difference, specially because you have no guarantee your tubes follow them at all.

    In fact I suspect modern tube makers just copy old datasheets so people think modern tubes are same as old ones ... I very much doubt that.

    If anything, and it worries you, get an "universal" OT like the original RS one (MM will love your cash input) or one ofn the Hammond ones or if you are really committed, a Turner Australia one , try different loads with *your* Tubes and pick the best by ear.

    If you are really comitted to experimenting, these Turner Audio transformers are the real deal: primaries split in 10 sections, secondaries split in 9 , all fully interleaved, by series-parallel combining sections on each side you can get a mind boggling set of combinations, such as anything from 560 ohm to 8k , all in the same OT.
    Basically he winds one layer and brings its ends out, so , say, 12 layers=12 separate windings, which you mix and match as you wish. Mind boggling possibilities and the Experimenterīs dream.
    I bet there is at least one model which you buy with a 100W core and allows you to build practically any Guitar Amp ever sold, go figure.
    for-sale-2-output-transformers



    Funny thing is, he gives all winding parameters in the descriptions, so these transformers can be cloned by a local winder .... I probably will build one or 2, a project for long cold boring Winters or endless raining seasons.
    wow that is the most photo detail about transformers ive ever seen. Some places won't even give out drawings of the case. I guess his business is good enough he doesn't care if someone copies stuff.

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    2 details:
    1) that way of winding transformers is **annoying** to say the least: you set up the machine for, say, 0.22mm wire (primary) .. wind 1 layer ... bring wires out ... set machine for 0.8mm wire (secondary) ... wire 1 layer ... rinse and repeat, switching wire, **adjusting advance screw and transfer wheel every time**
    Maddening job.
    It *might* be more practical nowadays if you have a CNC controlled winder, where advance screw is driven by a computer controlled stepper motor and adequate software, but I am certain he did that "by hand".
    Even with conventional winders itīs more reasonable if you use a "stick winder", where you wind, say, 8 coils at the same time on a single full sheet of Nomex or Mylar , do the same job as I mentioned above but at least you end up with 8 identical coils and not just 1.
    Then the 3 or 4 ft long "stick" is cut into 8 individual coils with a special fine toothed band saw.
    But this presumes high volume Commercial production, not practical for one-offs as Mr Turner did in his day.

    2) Heīs an old guy, retired since 2012 or so, heīs just selling remaining stock (which may take years), last page update was in 2016 or 2017, just *hope* heīs still among us
    Donīt think he currently worries too much about market share or competition.

    3) in a way, that winding method can be better hand-made, no need for expensive complicated machines when you can just hand guide wire, and let it self space, easier done than explained.
    All you need is one of these:


    and a little patience

    In fact, I would not be surprised at all if thatīs how he wound those.

    As a side note, a friend of mine, successful Tube amp maker, has a similar machine, but driven by a plain cordless screwdriver.
    Heīs wound hundreds of Transformers so far.
    Low RPM lets him hand guide wire with little effort.

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    Juan Manuel Fahey

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    Quote Originally Posted by J M Fahey View Post
    2 details:
    1) that way of winding transformers is **annoying** to say the least: you set up the machine for, say, 0.22mm wire (primary) .. wind 1 layer ... bring wires out ... set machine for 0.8mm wire (secondary) ... wire 1 layer ... rinse and repeat, switching wire, **adjusting advance screw and transfer wheel every time**
    Maddening job.
    It *might* be more practical nowadays if you have a CNC controlled winder, where advance screw is driven by a computer controlled stepper motor and adequate software, but I am certain he did that "by hand".
    Even with conventional winders itīs more reasonable if you use a "stick winder", where you wind, say, 8 coils at the same time on a single full sheet of Nomex or Mylar , do the same job as I mentioned above but at least you end up with 8 identical coils and not just 1.
    Then the 3 or 4 ft long "stick" is cut into 8 individual coils with a special fine toothed band saw.
    But this presumes high volume Commercial production, not practical for one-offs as Mr Turner did in his day.

    2) Heīs an old guy, retired since 2012 or so, heīs just selling remaining stock (which may take years), last page update was in 2016 or 2017, just *hope* heīs still among us
    Donīt think he currently worries too much about market share or competition.

    3) in a way, that winding method can be better hand-made, no need for expensive complicated machines when you can just hand guide wire, and let it self space, easier done than explained.
    All you need is one of these:


    and a little patience

    In fact, I would not be surprised at all if thatīs how he wound those.

    As a side note, a friend of mine, successful Tube amp maker, has a similar machine, but driven by a plain cordless screwdriver.
    Heīs wound hundreds of Transformers so far.
    Low RPM lets him hand guide wire with little effort.
    Thanks Juan, great post. Im a bit too much of a project glutton, get too many things going at once. Character flaw. But I would absolutely love to learn more about how to do this, and actually build a few output transformers. Do you ever see these hand winding machines onsale online used? Must be a fairly rare tool.

    Re output transformers you mentioned winding one layer. Wow, ONE layer at a time? for a typical double ended amp (2 x 6v6 or 6L6, 8k range pri) how many layers do you wind? So, you wind each layer, one pass, then solder the ends together between the same side layers? Where do you do all the soldering? I tore apart a few dead transformers back in the day (dead ones) and don't recall seeing very many soldered connections, looked like a couple of big loops. Maybe they were crappy transformers, though.

    Also, do you keep winding, then measure along the way, or only go by dc resistance of the total length of wire (i.e. theoretical resistance vs measured)?

    Do you put paper between the layers, so the layers sit close together? (I can think of way too many questions that would make this post way too long).

    ****
    Back to the original question, after I started reading various blogs, some people said the original original marshalls were 'too close' to edge of design, and sometimes burned up the output transformers if you used the wrong output impedance. Not sure if it was hearsay or fact or a mix. Also, didn't know that you could swap in, say 6.6k vs 8k for the same tube set, without something terrible happening.

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    Quote Originally Posted by mikepukmel View Post
    Thanks Juan, great post. Im a bit too much of a project glutton, get too many things going at once. Character flaw. But I would absolutely love to learn more about how to do this, and actually build a few output transformers. Do you ever see these hand winding machines onsale online used? Must be a fairly rare tool.
    Actually they are quite common, and quite inexpensive, the simplest being a piece of iron pipe holding a shaft, with a hand wheel at one end and a simple transformer bobbin holder at the other.
    Not even a counter, you count in your mind and , say, every 100 turns add a tick mark on a piece of paper, or you mod a pocket calculator as counter, search the proper yt Video.

    I suggest straight driving the shaft with a cordless drill.
    I have one for prototypes, basically like this one:

    Re output transformers you mentioned winding one layer. Wow, ONE layer at a time?
    you aalways wind a layer at a time.
    Usual way is you fill one layer, apply a sheet of insulating paper (pressphan) or Mylar/kapton/nomex, then wind next layer, and so on.
    You only bring out fullb section ends.
    What is special in Turner is that he brings each layer ends separate, he cuts the wire leaving pigtails, he then winds another with different diameter wire, again brings pigtails out, until he finishes it.
    He states it: 10 primary layers (each one may have, say, 50/80 turns, whatever fits) , interleaved with 9 secondary layers, again all brought out separated.
    Allows VERY fine adjustment of impedance, both plate and speaker, and of course is EXPENSIVE.

    "Normal" transformers, say Marshall, are not that detailed (unnecessary for Guitar), typically wind half primary (which may be 4 or 5 layers) , 0 to 4 ohm secondary (say, 2 or 3 layers of thicker wire), 1/4 primary, 4 to 16 ohm secondary (with an 8 ohm tap), remaining 1/4 primary.

    In USA a good transformer can cost some U$60, about 1 hour bench rate, and Mail is relatively inexpensive and fast, so 99% of people just buy one.

    In Argentina, Brazil, and many Countries of the World, same transformer climbs to U$120 because of freight and Customs, easily takes 30 days to arrive and be liberated, and bench rates are much lower (in U$) so it pays to have a local winder make one.
    Lots of people in Europe are discovering excellent Polish winders.
    for a typical double ended amp (2 x 6v6 or 6L6, 8k range pri) how many layers do you wind? So, you wind each layer, one pass, then solder the ends together between the same side layers? Where do you do all the soldering? I tore apart a few dead transformers back in the day (dead ones) and don't recall seeing very many soldered connections, looked like a couple of big loops. Maybe they were crappy transformers, though.
    Not that detailed, see above.
    4 or 5 (or 15) layers are wound with one continuous wire, no soldering needed if you do not cut it to begin with.
    Also, do you keep winding, then measure along the way, or only go by dc resistance of the total length of wire (i.e. theoretical resistance vs measured)?
    You count turns, which is the important parameter.
    Do you put paper between the layers, so the layers sit close together?
    Yes, always.
    Only transformers which are "scramble wound" , meaning not layer by layer, nor even wire smoothly side by side simply because itīs not practical, is smallest of the lot, those in wall warts, maybe a Reverb driver , which use very thin wire, impossible to control with precision.
    Similar to winding pickups and for the same reason.

    Mind you, I often see relay coils, microphone transformers, etc. , smoothly wound with very fine wire, but I guess those are VERY expensive machines.
    Back to the original question, after I started reading various blogs, some people said the original original marshalls were 'too close' to edge of design, and sometimes burned up the output transformers if you used the wrong output impedance. Not sure if it was hearsay or fact or a mix.
    Not sure, such early amps are Collectorīs stuff and never reach these shores, so never saw one on my bench.
    Also, didn't know that you could swap in, say 6.6k vs 8k for the same tube set, without something terrible happening.
    Nothing terrible.
    In fact most tube amps can tolerate up to 2:1 mismatch, meaning double or half impedance, certainly wonīt care about meager 20% (the difference between 8000 and 6600 )
    In fact my generic OT for a couple 6L6 or EL34 is 5500 ohm to 4 ohm (sometimes 8 ohm)
    WHY?
    Because my experience is that practically *any* tube, *any* brand is happy with that load, and gives me honest 40W clean which is more than enough for Club play.
    Imagine not having to *agonize* over tube brand, date, NOS vs modern, ultra careful biasing, etc.
    All work unless very worn or dead.
    4000 ohm plate to plate which is more of a classic load *can* give me 50W ... but amp becomes more choosy, is not happy with all, requires more precise matching, after 1 or 2 years tubes start showing their age, etc.
    All for 10W extra.

    A Forum Member, kmz6x , lives in Russia for over 10 or 15 years now.
    he used to have the largest Service Shop in the San Francisco area, was *the* Factory service for lots of brands , but got fed up with a lot of things and moved to St Petersburg, swearing he would never plug in a soldering iron again.
    But you know, this is a virus we all carry inside, and after some time he started again, as a hobby (his main Business now is Tourism, big time) .

    He was *amazed* at getting at his new tiny Lab-in-an-appartment-room amps for servicing, most Tube type of course, from Artists such as "Uncle Ivan and his amazing accordion" , the King of Weddings, Birthday parties, Baptisms and any other social or Family party, working 6 nights a week, non stop, for the last 30 or 40 years ... most with the *original* tubes !!!!!!!
    And still working, although at reduced output.
    He couldnīt believe it, until he found all those amps (made in the 60īs and 70īs) used the tubes "by the book", exactly under those conditions "nobody uses", at least not Leo, Jim or Dick.
    Hereīs what the old RCA datasheet says:

    Click image for larger version. 

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    I don't quite have a mental picture of how you'd wind a OT with one continuous piece of wire for each winding, without cutting and soldering. Can you finish the current loop, then mount the spool someplace and let that spin around while winding the next loop of the other winding? It looks like the winders are all made to run off one spool.

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    Old Timer J M Fahey's Avatar
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    Not sure about your doubt, but in any case: suppose Iīm winding a *simple* 50W Fender OT, 4000 ohm plate to plate primary, 4 ohm secondary.
    This is the most basic OT design which "works".

    Primary is wound with about 0.25mm diameter wire, you set wire guide advance screw for that diameter for even winding.

    You put the plastic bobbin on the winder holder, start winding the first layer and end to end you will fit about 140/150 turns.
    Wire beginning exits through a bobbin side hole for later connection.

    You wrap around that first layer a 0.1mm sheet of Mylar or treated paper, itīs about the thickness of regular printer paper, you hold it with a piece of tape.

    Then you wind the second layer, which again is wrapped in insulator paper, and so on and on, layer by layer, until you wind half primary.
    We are talking, say, almost 1000 turns so you have about 6 layers of primary wire.

    Until now, wire simply "continued on the top next layer", without cutting or soldering anything, itīs a continuous wire.

    When you finish, you bring out the end and now cut it.
    You end with 2 pigtails which are the ends of half primary winding.

    You wrap two insulation layers for safety, set machine advance screw for 1mm to 1.25mm (secondary) wire , obviously you have less turns per layer, say 30 to 40, so usually 2 layers are enough.

    Again double insulation thickness and you wind remaining half primary.

    So you end with 6 pigtails: for 2 half primaries and a single secondary.
    You burn/scrap insulation, twist and solder whatever you need and solder colour wire leads for identification.

    This is a somewhat crude way of doing it, but gives you the visual image:


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    Thanks for the video Juan, sorry for the stupid question, ok I think Ive got it. Start with thin ga wire. Wind a whole bunch of turns, one piece. This is wind 1. When you're done with wind1, stop, bring the ends out, tape. Start with wind2 (thicker wire). Wind a bunch of turns. When you're done with wind2, stop, bring the ends out, cut. And so on. So, each wind, i.e. a wind for a particular gauge, may have many layers, all in one piece, but when its done, you bring the ends out and cut them so you can switch gauge.

    That was the part I didn't "get". I thought they had some way to interleave 2 different gauge wire, and EACH gauge was one continuous piece throughout the whole transformer, so you only had, say 2 ends for each gauge at the end. Can't do that. Will have 2 ends for each wind, each interleave.

    It must, then be fairly critical or at least important, how you join the ends. I mean, the charge travels through the wire in a particular direction. If you connect the ends wrong, then instead of cooperating, you might make two wind's battle each other. (right hand rule for B field around the wire, they all need to rotate so they cooperate between winds)

    Also, the wire has to be stripped a bit, and what do you do put heat shrink or some kind of shellac over the joints?

    An aside, unrelated, the Australian guy who is now retired, wrote on his pages that he had originally bought metal for the cores from a company that aligned the iron molecules a certain way during manufacture, and that they don't make those plates any longer. Wondering if some high end company,like McIntosh buys stuff like that.

    ***
    I think I found a new hobby!

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    Aside, I don't like the new "like" and "dislike" buttons so much. I used to just like "like" not necessarily, because I like the post (most often I really do) but more of a "Thanks for posting" kind of thing. I have to check 3 times now that I didn't click "unlike" which, I don't think id ever do.

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    So that's how they wind toroids!

    https://www.youtube.com/watch?v=tT44CnqH15I

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by mikepukmel View Post
    Start with thin ga wire. Wind a whole bunch of turns, one piece. This is wind 1. When you're done with wind1, stop, bring the ends out, tape. Start with wind2 (thicker wire). Wind a bunch of turns. When you're done with wind2, stop, bring the ends out, cut. And so on. So, each wind, i.e. a wind for a particular gauge, may have many layers, all in one piece, but when its done, you bring the ends out and cut them so you can switch gauge.

    That was the part I didn't "get". I thought they had some way to interleave 2 different gauge wire, and EACH gauge was one continuous piece throughout the whole transformer, so you only had, say 2 ends for each gauge at the end. Can't do that. Will have 2 ends for each wind, each interleave.

    It must, then be fairly critical or at least important, how you join the ends. I mean, the charge travels through the wire in a particular direction. If you connect the ends wrong, then instead of cooperating, you might make two wind's battle each other. (right hand rule for B field around the wire, they all need to rotate so they cooperate between winds)
    Yes, thatīs why you keep careful track on hich end is start, which end is finish, so they are connected in phase (exactly like speakers in series in a cabinet).

    Also, the wire has to be stripped a bit, and what do you do put heat shrink or some kind of shellac over the joints?
    Canīt trust shellac, I (and most) normally use paper tape, but heatshrink is a deluxe option.

    An aside, unrelated, the Australian guy who is now retired, wrote on his pages that he had originally bought metal for the cores from a company that aligned the iron molecules a certain way during manufacture, and that they don't make those plates any longer. Wondering if some high end company,like McIntosh buys stuff like that.
    Fancy way to say he used grain oriented silicon steel strips.
    I forgive HIM, heīs not actually lying

    You can get such strips any day of the week (hey, *I* can even being in Argentina, and within 30 minutes driving from my home ), and I guess some grain oriented C cores are still made somewhere; Audiophile Market is very small but still exists.

    Hey!!! look what the cat brought!!!:
    http://www.bridgeportmagnetics.com/c...2_C-Cores.html

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