Winding 30W Amp Transformers

[katopan]

Ah, that's why there's so much interleaving. Thanks Sagitt.

[katopan]

Winding wire is now ordered and should arrive tomorrow. I've also started to disassemble the old transformer. Bit more on that tonight and I should have myself a nice couple of stacks of lams.

[katopan]

I just finished the disassembly of the old transformer. Came apart fairly easily but now my fingertips have a smooth waxy feel to them.

Here's a couple of pics (sorry for the bad focus but I packed everything away before checking) of testing the fit of my home made bobbins. 1.25" stack for the OT and 2.25" stack for the PT. Everything looks good. The clearance around the centre leg would probably be a touch closer on a nylon cast bobbin, but it's still pretty good, they sit square and have just the right clearance at the sides.

[sagitt]

I see yuo use EI 96 core size for your PT...no way you can fitt all that wire in that window!for my exspress PT I use EI 108 core,36x45mm.for that power you will need 0.63mm primary wire,I use 0.65mm,for secondary 0.33-0.34mm and it is enough for 0.225A!STANCOR P-8164 PT is rated 0.225A too...for two EL34 and output power 30-35W plate current would be about 190-200mA max I think?I didnt use any isolation between layers except primary and secondary.all hand-wound!I noticed if you hand-wound PT,overall output voltage without load is sensibly bigger,probably because it will have less copper losses.most important thing is that PT runs pretty cold!

[sagitt]

this days I would try to wind PT for liverpool...EI 108 core 36x38mm, and I will try to put isolation between each layer of wire,it is gona be nomex 0.05mm.I will post the pictures too,maybe it help someone...

[katopan]

So you've come up with the same answer as me in that you can't fit the required copper into the winding window of US EI-125 (or DIN EI96) for that size PT. Your DIN EI108 lines up with the US EI-137 I worked out earlier in the thread. But yet photos of real Express amps show EI-125 being used for the PT and OT (same height as the EL34s) and transformers available for clone amps are the same. Interesting isn't it....

There's just no way the wire of the right diameter will fit for the secondary current ratings that are quoted. So that tells me they've taken shortcuts, and I'm not just talking about the clone transformers but the originals too. Either in wire size or in turns, probably both. But at the end of the day they work and have been for many years. So I'm going to follow the same road and accept that my PT will run warm.

[sagitt]

yeah man,PT and OT are the same size!I was looking all this PT pictures and asking my self how it is possible that the PT is the same size as OT!they probably use different current density per mm2...I would really like to lay my hands on that PT and OT and disassemble them...buy one burned out maybe...

[katopan]

Yeah, they've got to be pushing current density and magnetic flux density for that core size.

OK we have a plan for the PT. Using the smaller wire diameters I mentioned above and no interlayer insulation (but I will use interwinding insulation of course) it should all fit if I keep my winding nice and neat.

The most I can fit is 26 layers of 50 turns/layer of the HT secondary. So 1300 turns, or 650 turns either side of the CT. Working out the magnetic flux density:
N = E / (4.44 x f x A x B)
rearrange to become:
B = E / (4.44 x f x A x N) = 300V / (4.44 x 50Hz x 18.15x10^-4 m2 x 650 turns) = 1.15T
Iron saturation depends on what grade it is, and I don't know what I've got. But 1.15T should be OK for any sort even though it's higher than what the rule of thumb calcs I did at the start of the thread are based around.

Secondary side:
Bobbin
Polyester film insulation
HT secondary 26 layers of 50 turns/layer, 0.315mm wire
Polyester film insulation
Heater secondary 2 layers with 13.8 turns total, 1.0mm wire x 2 parallel windings
Polyester film insulation
Paper label

Pulling out taps one layer either side of the P1 & P2 wires of 50 turns/layer will give me 275V taps on the 300V x 2 winding. This is for potential reduced B+ for 6V6s.

Primary side:
Bobbin
Polyester film insulation
15 layers of 33 turns/layer with 491 turns total, 0.5mm wire
Polyester film insulation
Paper label

240V primary winding will be tapped at 471 turns for a 230V tap. I may wind the extra 20 turns and make the primary 250V (we get quite elevated mains voltages in some areas) with 240V & 230V taps.

Phew! I think this is actually going to work.

*Edit* And my winding wire just arrived.

[katopan]

Man, three weeks later and I'm still not winding yet. This turns counter circuit is taking forever to put together! Hasn't been much free time in the lead up to Christmas.

Anyway, I've put together the attached winding charts. This will help me keep track of everything as I go. Very important to tick off layers as you go because loosing track would ruin the transformer. Everything is in place and I've got all the materials ready to make a start once I finish the counter.

I've added 275V and 225V taps on the 300V HT secondary. 300V like normal for EL34s, the 275V is the lower voltage for 6V6s and the 225V will let me experiment with some lower voltage power valve options.

[C Moore]

Another interested onlooker.
The suspense is really building..!!!
best

[katopan]

Before Christmas got busy, the festive season was, well, festive, and in Jan work was flat out. But I'm now on holidays so should be able to finally make some progress on winding these transformers.

I fired up my turns counter today. Messy, yes, but it functions and was put together quickly - the only two goals of building one. Added a connection missing on the front end comparator and it all worked. Runs off a 9V pedal power supply, and connects to a reed switch on my home-made hand winder which I already had from last time I wound my own. Reset P/B sticks through the enclosure.

I've now got all the materials together and will post some winding photos soon.

[katopan]

All set up and ready to go! Power transformer winding pics to followup with tomorrow.

[JazzGuitarGimp]

Let the fun begin!

[katopan]

I wasn't going to post these until I'd soldered on the primary flying leads, but here's a sneak peak at all I'm going to get done today.

PT_1: Let the fun begin indeed! Layer of mylar sheet (overhead transparency) superglued to my cardboard bobbin (doesn't show up in the photo) and the 240Vac tap.

PT_2: First half layer to the 230Vac tap.

PT_3 & PT_4: Primary winding all wound with a couple of coats of clear fingernail polish. First step tomorrow will be a layer of mylar sheet, then solder the flying leads, then another bit of mylar just over the soldered connections. I'll add the label on top when I've finished both sides. After the primary is finished I should have time to be able to make a decent start on the secondary.

[Structo]

Sweet!

What kind of sensor is used on your counter?