Hi,
I am newbie on the tube amp area and I decided to build my first tube amplifier (SE Class A). I purchased from Toroidy (Poland) two pieces of tube single ended toroidal output transformers.
For a long period and especially during Christmas holidays, I worked hard to make it work in the usual topology (Anode , Ultra Tap, V+) as it was also recommend on the label on the OT, but it was not possible.
After a lot of trials and searching on the internet, I found out that the only topology that could work is by using a parafeed circuit , but this configuration is poor for the sound and at the end more expensive.
Before going back to using normal OT, has anyone find any solution on how to actually use them? Has anyone use toroidal OT from this company?
Bob D.
I am newbie on the tube amp area and I decided to build my first tube amplifier (SE Class A). I purchased from Toroidy (Poland) two pieces of tube single ended toroidal output transformers.
For a long period and especially during Christmas holidays, I worked hard to make it work in the usual topology (Anode , Ultra Tap, V+) as it was also recommend on the label on the OT, but it was not possible.
After a lot of trials and searching on the internet, I found out that the only topology that could work is by using a parafeed circuit , but this configuration is poor for the sound and at the end more expensive.
Before going back to using normal OT, has anyone find any solution on how to actually use them? Has anyone use toroidal OT from this company?
Bob D.
This what I found out, but the company sold me the OT (I told them I want to build SE amp) and I thought maybe there is some sort of solution.
Thanks for replying.
I build a SE Class A amp.
The first symptom was a lot of distrortion. I checked everything and both channels had the same behaviour. I used oscilloscope and a 1KHz sine generator and at the output of the final stage (just at the OT) the upper part of the sine was flattened (cut).
I put a dummy load and measured on the load the same "cut" sinewave.
Then I searched on the internet and found that this topology is not working.
I am asking here, because I am a newbie and maybe there is a solution.
The first symptom was a lot of distrortion. I checked everything and both channels had the same behaviour. I used oscilloscope and a 1KHz sine generator and at the output of the final stage (just at the OT) the upper part of the sine was flattened (cut).
I put a dummy load and measured on the load the same "cut" sinewave.
Then I searched on the internet and found that this topology is not working.
I am asking here, because I am a newbie and maybe there is a solution.
Toroidy have sold SE toroidal OPTs for quite a long time. http://sklep.toroidy.pl/en_US/c/Single-Ended/139
Would it be likely that only now a newbie is the first person to find out that the SE toroids made by this polish company do not work ???
The engineers of the company have noticed nothing, just produced lot of toroids that do not work ???
This does not contain much info. What output tube? What supply voltage? What idle current? Can you post the schematic. And what OPT ?
High distortion is typical to SE topology.
Didi you get the expected output power ( or voltage to the load) ?
Can you post a photo of the above measurement ?
Would it be likely that only now a newbie is the first person to find out that the SE toroids made by this polish company do not work ???
The engineers of the company have noticed nothing, just produced lot of toroids that do not work ???
This does not contain much info. What output tube? What supply voltage? What idle current? Can you post the schematic. And what OPT ?
High distortion is typical to SE topology.
Didi you get the expected output power ( or voltage to the load) ?
Can you post a photo of the above measurement ?
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Of course I do not judge the company, but my question has to do with the use of toroidal OT in SE amps.
If someone has succesfully used toroidal OT in a SE amp, I would like to hear it and then I will start again.
Currently the amp is beeing "decomposed" in order to rebuild it in another chassis, using classic OT.
Thanks for the help,
Bob
If someone has succesfully used toroidal OT in a SE amp, I would like to hear it and then I will start again.
Currently the amp is beeing "decomposed" in order to rebuild it in another chassis, using classic OT.
Thanks for the help,
Bob
I still understand your comment so that you seriously think that you are the first person (including the manufacturer) to observe that SE toroidal OPTs do not work at all.
I have not built any SE-amplifier with toroidal OPT, but I know that several well working have been built here in Finland by my friends.
So I f you want help, I suggest that you focus on to provide answers to the questions done for you above.
Toroidal transformers are sort of the "perfect" transformer: an almost perfect coupling of primary to secondary, leading to low losses, low stray emissions, and as such low weight when compared to EI. But it all stops when DC is applied: EI can tolerate some, toroidals can't. And indeed, one can cut a gap in a toroidal, which IMHO defeats the purpose of using it, but anyway.
Plitron seems to be quite succesfull with SE toroidal OPTs and DC chokes - so it can be done.
I bought and tested some Toroidy DC chokes and found out thez didn't work as DC chokes. Toroidy confirmed this, refunded my purchase, and got a new core for their chokes, which I haven't tested yet. I also didn't test their SE OPTs.
Clipping could be due to lack of inductance caused by core saturation due to DC current. Or the circuit clips because of poor operation points. Before judging the trafos it would be great if you could post the schematic with measured DC (and AC) conditions: voltages and currents at the different points of the amplifier.
Best regards,
Erik
Plitron seems to be quite succesfull with SE toroidal OPTs and DC chokes - so it can be done.
I bought and tested some Toroidy DC chokes and found out thez didn't work as DC chokes. Toroidy confirmed this, refunded my purchase, and got a new core for their chokes, which I haven't tested yet. I also didn't test their SE OPTs.
Clipping could be due to lack of inductance caused by core saturation due to DC current. Or the circuit clips because of poor operation points. Before judging the trafos it would be great if you could post the schematic with measured DC (and AC) conditions: voltages and currents at the different points of the amplifier.
Best regards,
Erik
Artosalo,
Well, I bought some of toroidy's DC chokes and they really didn't work as advertised - I posted measured results here and it evolved in quite a thread. I don't blame Toroidy, because they were comprehensive, refunded me, and introduced a new line of chokes (which I didn't test).
Still it surprised me that nobody else perceived this: I guess I wasn't the only person who bought these chokes. I assume other people do build and don't test, and OTOH it is quite probable that quite a lot of these chokes just end up on a shelve for a "future project" so never get used at all.
best regards, Erik
To make myself clear I never said that it is not possible to build a SE with toroidal OPTs. Since I am a newbie, I just connected the toroidal to where the normal OPT goes and this is not working. Searching the internet,
I found solutions with chokes and capacitors, (parafeed?) which I wouldn't prefare to implement.
Thanks for your help,
Bob
Distortion "on the top" is typical of a mis-biased SE power stage.
As you have not told us your tube, your load impedance, idle current or voltage, we can't guess if this may be the case.
Optimizing a SE stage is not a simple process. After decades of using SE, in a recent project I spent a month with various bias and loading.
Good iron can be "too good" for a choke (transformer) with DC current. You can just use more iron. Or a lower grade of iron. Or an air-gap. EI cores naturally have some air-gap, which can be shimmed if needed. Torroids don't have that, but more or different iron or some mechanical cleverness can find a workable design. I'm sure the company knows all this in detail.
I hate to spend your money, but how about dropping on a low-price EI core to see if the problem changes? The Hammond 125SE series works good in the 150-5KHz range, though the choice or primary impedance is limited (unless you stock odd-value dummy resistors for the secondary).
As you have not told us your tube, your load impedance, idle current or voltage, we can't guess if this may be the case.
Optimizing a SE stage is not a simple process. After decades of using SE, in a recent project I spent a month with various bias and loading.
Good iron can be "too good" for a choke (transformer) with DC current. You can just use more iron. Or a lower grade of iron. Or an air-gap. EI cores naturally have some air-gap, which can be shimmed if needed. Torroids don't have that, but more or different iron or some mechanical cleverness can find a workable design. I'm sure the company knows all this in detail.
I hate to spend your money, but how about dropping on a low-price EI core to see if the problem changes? The Hammond 125SE series works good in the 150-5KHz range, though the choice or primary impedance is limited (unless you stock odd-value dummy resistors for the secondary).
Toroids are used in many applications where an air gap is needed. These toroids are called "Distributed Air Gap Toroids. Quote: In some applications it is desirable to have an air gap in the core path. For mechanical reasons, it is cumbersome to add air gap to a toroid. Large air gaps produce undesirable flux fringing. Powdered cores combined the magnetic material with a non-magnetic binder material. Magnetically, the binding material acts like an air gap, but this gap is distributed throughout the entire core. Because of this distribution there are no flux fringing effects. The binder(s) also reduce eddy currents."
Yes, we are all wanting to see a schematic of your amplifier, with tube types, parts values, etc.
What is the specified primary impedance of the Toroidy transformers you have?
We are here to help.
Then we can determine if it will work properly with standard E-Air Gap-I transformers, and if it will work with some Toroid transformers (i.e. with Plitron SE models).
I suspect that the Plitron SE Toroid transformers use a very thin spacing material (plastic tape or thin paper) between the many wound layers of the very long steel tape lamination. The Platoon SE transformers do work with DC in the primary (I have a friend who used them successfully).
But that does not mean that the Toroidy model(s) will work with DC in the primary.
Once we have determined the circuit and parts values are OK, then we can determine what steps to take next:
Adjust parts values.
Test the tubes.
Use air gapped SE output transformers ...
Or ... add a plate choke and a coupling capacitor so you can use the Toroidy transformers in Parafeed operation.
What is the specified primary impedance of the Toroidy transformers you have?
We are here to help.
Then we can determine if it will work properly with standard E-Air Gap-I transformers, and if it will work with some Toroid transformers (i.e. with Plitron SE models).
I suspect that the Plitron SE Toroid transformers use a very thin spacing material (plastic tape or thin paper) between the many wound layers of the very long steel tape lamination. The Platoon SE transformers do work with DC in the primary (I have a friend who used them successfully).
But that does not mean that the Toroidy model(s) will work with DC in the primary.
Once we have determined the circuit and parts values are OK, then we can determine what steps to take next:
Adjust parts values.
Test the tubes.
Use air gapped SE output transformers ...
Or ... add a plate choke and a coupling capacitor so you can use the Toroidy transformers in Parafeed operation.
I hate automated computer spelling software that replaces the word Plitron with Platoon
(there is no group of Army men in a toroidal transformer).
I did not notice the word Platoon that was automatically inserted in my previous post
(I caught the first one, but not the second auto-replacement).
Software and I do not get along (anybody else for automation?).
I get along much better with point to point wiring of vacuum tube amplifiers (I can do it without a schematic). Any mistakes I make are on me, not the writer of the software).
(there is no group of Army men in a toroidal transformer).
I did not notice the word Platoon that was automatically inserted in my previous post
(I caught the first one, but not the second auto-replacement).
Software and I do not get along (anybody else for automation?).
I get along much better with point to point wiring of vacuum tube amplifiers (I can do it without a schematic). Any mistakes I make are on me, not the writer of the software).
so can you please show us some tube output transformers with iron powder core?
Distributed air gap toroids (powder iron) have very low permeability and are not suitable for SE use.
For SE or DC chokes toroidal core is being cut in one place with band or disk saw (e.g. 0.5 or 1mm thick) and then filled with compound, or in 2 or more pcs for assembly in a cage, with thick epoxy layers between pieces.
I don't know if its possible to make gapped core with technique you have described. Wound core needs to be heat annealed, so plastic ribbon is very likely to melt and burn.
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PS. I'm in doubt it makes any sense to make toroidal SE transformer. As I mentioned before, it limited to fixed air gap thickness because of machinery, thus, its geometry and winding can't be optimized to the same extend as conventional ones. On the other hand, gap in double C core is easily adjustable with plastic film layer(s) to almost any meaningful value. In short, its more like fetish rather then measure of quality.
Attachments
There are some radio amateur radio transmitters that use Powdered Iron Core transformers in Push Pull RF amplifiers.
Oh ... and Push Pull RF amplifiers cancel the DC in the core.
I have never seen any powdered Iron Core Audio transformers, but I believe I have seen advertisements for them. I have never purchased such transformers.
I like M6 and similar lams for both my SE amps, and for my push pull amps.
I am personally not a fan of "early saturation" exotic core materials.
I have never purchased those.
For Push Pull amps, whenever I am worried enough about zero crossing distortion on M6 in Push Pull output transformers, I use a pair of air gapped SE transformers, one for push and one for pull, and then I wire the secondaries in anti-phase parallel. That eliminates the magnetic zero crossing distortions for push pull.
But usually I don't worry, so I use standard lams push pull transformers.
And I use standard lams air gapped SE transformers for the SE amps.
Oh ... and Push Pull RF amplifiers cancel the DC in the core.
I have never seen any powdered Iron Core Audio transformers, but I believe I have seen advertisements for them. I have never purchased such transformers.
I like M6 and similar lams for both my SE amps, and for my push pull amps.
I am personally not a fan of "early saturation" exotic core materials.
I have never purchased those.
For Push Pull amps, whenever I am worried enough about zero crossing distortion on M6 in Push Pull output transformers, I use a pair of air gapped SE transformers, one for push and one for pull, and then I wire the secondaries in anti-phase parallel. That eliminates the magnetic zero crossing distortions for push pull.
But usually I don't worry, so I use standard lams push pull transformers.
And I use standard lams air gapped SE transformers for the SE amps.
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