That paper bobbin reminds me of my scale paper airplane model days.
Anyway, just for future reference, you may want to check this thread on making a bobbin out cotton cloth laminate (textolite?). It's in polish but the photos are self explanatory.
http://www.trioda.com/forum/viewtopic.php?f=7&t=22920
Winding 30W Amp Transformers
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VacuumVoodoo
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Re: Winding 30W Amp Transformers
Aleksander Niemand
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Life's a party but you get invited only once...
affiliation:TUBEWONDER AMPS
Zagray!-review
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Life's a party but you get invited only once...
affiliation:TUBEWONDER AMPS
Zagray!-review
Re: Winding 30W Amp Transformers
heavy interleaved monster...
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Re: Winding 30W Amp Transformers
Nice work Sagitt. That looks like a nice job. What size is that one and what amp is it for?
I just finished the second coat of varnish on both bobbins, so they're now finished. Now I've got to order some wire and finish off my counter circuit.
I just finished the second coat of varnish on both bobbins, so they're now finished. Now I've got to order some wire and finish off my counter circuit.
Re: Winding 30W Amp Transformers
EI96,for Express...laminations are 96x80mm,this is the amp,I made the PT to!sorry for tit! 
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Re: Winding 30W Amp Transformers
Aren't varistors usually considered to be "sacrificial?" They eat up a certain number/size of spikes and then are toast? If so, it would kind of a pain to have them internal.VacuumVoodoo wrote:Varistors eat voltage transients, they go short circuit when voltage transient exceeds specified limit and dissipate that energy as heat. Specs in data sheets are for threshold voltage and dissipated energy in joules.katopan wrote: Are there varistors built into the OT primary windings or are they external? They could be anything depending on if they're PTC or NTC. Inrush current limiting or thermal protection? I have no idea without more info. Wasn't planning on putting anything but enamelled copper in my windings!
Info on Toms page is generally solid but there are few booby traps, whether intentional - I don't know.
Re: core stacks, those oblong EI stacks are not optimal. Total transformer performance drops when central column (the "-" in E) cross section departs too far from a square and becomes a long rectangle. I wouldn't recommend higher ratio of length to width than 1,5 but opinions certainly vary. From transformer factory point of view it's cheaper to stock fewer lamination sizes.
Re: Winding 30W Amp Transformers
Sagitt - Looks good! (Amp, not the rubber tit. 
) Obviously your transformer placement is not standard. Is you layout internally the standard layout?
Firestorm - Like ones with fuses in the windings. One mistake and you've got a doorstop.
) Obviously your transformer placement is not standard. Is you layout internally the standard layout?Firestorm - Like ones with fuses in the windings. One mistake and you've got a doorstop.
Re: Winding 30W Amp Transformers
What I thought. Supposedly very old Fenders had PTs they opened and added resistors to (per Alex Dumble, via Mike DeTemple). That would be a service nightmare, too.katopan wrote:Sagitt - Looks good! (Amp, not the rubber tit.
Firestorm - Like ones with fuses in the windings. One mistake and you've got a doorstop.
Re: Winding 30W Amp Transformers
That is a very cool way to make a bobbin.VacuumVoodoo wrote:That paper bobbin reminds me of my scale paper airplane model days.
Anyway, just for future reference, you may want to check this thread on making a bobbin out cotton cloth laminate (textolite?). It's in polish but the photos are self explanatory.
http://www.trioda.com/forum/viewtopic.php?f=7&t=22920
You could use 1/16" garolite or similar to make that.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: Winding 30W Amp Transformers
layout is totally different,part placement to!Amp is dead quiet...katopan wrote:Sagitt - Looks good! (Amp, not the rubber tit.
Firestorm - Like ones with fuses in the windings. One mistake and you've got a doorstop.
Last edited by sagitt on Mon Nov 26, 2012 2:22 pm, edited 1 time in total.
Re: Winding 30W Amp Transformers
I am interested in winding this 50W Marshall OT!do you have exact numbers to share or it is a secret and how did you get this nubers for your 6K6 OT?are you cloning already known OT?
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JazzGuitarGimp
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Re: Winding 30W Amp Transformers
I think all the electrons are obediently "towing the line" and being "vewwwwy kwiiiiiiet, in shock by the site of the teat!sagitt wrote:layout is totally different,part placement to!Amp i dead quiet...katopan wrote:Sagitt - Looks good! (Amp, not the rubber tit.
Firestorm - Like ones with fuses in the windings. One mistake and you've got a doorstop.
Lou Rossi Designs
Printed Circuit Design & Layout,
and Schematic Capture
Printed Circuit Design & Layout,
and Schematic Capture
Re: Winding 30W Amp Transformers
I was thinking you might say that. Dead quiet is always good!sagitt wrote:layout is totally different,part placement to!Amp is dead quiet...
Numbers for this OT I'm winding are guessed using the OTs I do know about and calculated for what will fit in the winding window with the construction I'm planning to use. Followed the interleave pattern from the Polish site I listed earlier. So no, it's not a known OT.sagitt wrote:how did you get this nubers for your 6K6 OT?are you cloning already known OT?
What about yours? Is it a proper Express interleave or based on something else?
Re: Winding 30W Amp Transformers
OK, I've been working the PT design and have hit a problem. I was a bit worried about getting all the turns to fit in the winding window and sure enough it's an issue. It's that damn smaller lam size being used with a rectangular stack that doesn't give as much window as a bigger lam and square stack.
So I based things on the numbers I worked out at the beginning of this thread. Won't fit by a mile! It's compromise time. I could use US EI-137 lams but I don't have any and it would be different externally to the Express PT. So sticking with what I've got there are three ways to reduce the space taken up by turns of wire: reduce the number of turns which will increase magnetic flux; reduce the wire diameter which will reduce current rating / run warmer for a known load current; and reduce insulation thickness or not use it.
Starting from the end of that list going backwards....
Putting paper insulation in between each layer is a traditional construction method. It adds additional robustness to a transformer, but plenty survive without it. I'm planning on still winding neat layers which is better than the scatter winding of many of today's PTs. So the baking paper layers won't be included.
I can't really decrease the heater winding diameter for the expected heater current load. But the HT secondary was just over the rating for 0.315mm wire so I rounded up to 0.4mm. If I take that back down to 0.315mm I've still got 230mA of rating (according to the table I use) instead of the design value of 250mA. Side effect will be it might run a bit warmer. 0.4mm has 360mA so it is overkill. Also the primary I sized based on full load with an additional 20% safety factor. If I reduce that to 10% (which is closer to the typical PT efficiency) I can go from 0.56mm/730mA down to 0.5mm/580mA. Both of these mean more turns per layer and therefore less number of layers.
I do all that and it still looks like my windings are going to bulge a bit out of the bobbin sides and I won't be able to insert the lams.
I also redid the turns calculations based on the actual core size of 1.25" x 2.25" = 18.1cm2.
turns/volt = 45 / S = 45 / 18.1 = 2.5
Heater secondary - 1.07 x 6.3V x 2.5 turns/volt = 16.85 turns -> round it to 17 turns
HT secondary - (1.07 x 300V) x 17 turns / (1.07 x 6.3V) = 809 turns x 2 windings
Primary - 240V x 17 turns / (1.07 x 6.3V) = 605 turns
After all that it still doesn't quite fit, so we resort to the last trick up the sleeve. I do calculate height based on stacking turns directly above each other where in reality they sit down in between each other a bit, reducing the overall height. Also it's getting close to fitting with the secondaries being the limit rather than the primary. I'm just going to have to wind it up starting with the HT secondary and see how many turns and layers it's going to fit, leaving room for the heater secondary on top. It'll be close and if the full 809 turns x 2 windings doesn't fit then I'll have to adjust the heater secondary and primary turns to keep the designed ratios.
The design calc method I used at the start of this post is conservative and would've resulted in a PT that runs pretty cool. By making these compromises it will run warmer. Obviously if I felt these were pushing things too far I would have to either make or buy a new bobbin with tighter tolerances or move to a larger lam size. But I'm comfortable so far. Not ideal but I think it will still deliver the goods. As for how much extra temperature rise I get, only building it will show. So that finalises the wire sizes. Better go buy some as the next step.
So I based things on the numbers I worked out at the beginning of this thread. Won't fit by a mile! It's compromise time. I could use US EI-137 lams but I don't have any and it would be different externally to the Express PT. So sticking with what I've got there are three ways to reduce the space taken up by turns of wire: reduce the number of turns which will increase magnetic flux; reduce the wire diameter which will reduce current rating / run warmer for a known load current; and reduce insulation thickness or not use it.
Starting from the end of that list going backwards....
Putting paper insulation in between each layer is a traditional construction method. It adds additional robustness to a transformer, but plenty survive without it. I'm planning on still winding neat layers which is better than the scatter winding of many of today's PTs. So the baking paper layers won't be included.
I can't really decrease the heater winding diameter for the expected heater current load. But the HT secondary was just over the rating for 0.315mm wire so I rounded up to 0.4mm. If I take that back down to 0.315mm I've still got 230mA of rating (according to the table I use) instead of the design value of 250mA. Side effect will be it might run a bit warmer. 0.4mm has 360mA so it is overkill. Also the primary I sized based on full load with an additional 20% safety factor. If I reduce that to 10% (which is closer to the typical PT efficiency) I can go from 0.56mm/730mA down to 0.5mm/580mA. Both of these mean more turns per layer and therefore less number of layers.
I do all that and it still looks like my windings are going to bulge a bit out of the bobbin sides and I won't be able to insert the lams.
I also redid the turns calculations based on the actual core size of 1.25" x 2.25" = 18.1cm2.
turns/volt = 45 / S = 45 / 18.1 = 2.5
Heater secondary - 1.07 x 6.3V x 2.5 turns/volt = 16.85 turns -> round it to 17 turns
HT secondary - (1.07 x 300V) x 17 turns / (1.07 x 6.3V) = 809 turns x 2 windings
Primary - 240V x 17 turns / (1.07 x 6.3V) = 605 turns
After all that it still doesn't quite fit, so we resort to the last trick up the sleeve. I do calculate height based on stacking turns directly above each other where in reality they sit down in between each other a bit, reducing the overall height. Also it's getting close to fitting with the secondaries being the limit rather than the primary. I'm just going to have to wind it up starting with the HT secondary and see how many turns and layers it's going to fit, leaving room for the heater secondary on top. It'll be close and if the full 809 turns x 2 windings doesn't fit then I'll have to adjust the heater secondary and primary turns to keep the designed ratios.
The design calc method I used at the start of this post is conservative and would've resulted in a PT that runs pretty cool. By making these compromises it will run warmer. Obviously if I felt these were pushing things too far I would have to either make or buy a new bobbin with tighter tolerances or move to a larger lam size. But I'm comfortable so far. Not ideal but I think it will still deliver the goods. As for how much extra temperature rise I get, only building it will show. So that finalises the wire sizes. Better go buy some as the next step.
Re: Winding 30W Amp Transformers
hell-o!interleaving for this OT is based on info that I find on turner audio page...