DIY Audio forum is talking about winding your own 5k tube audio transformer. I joined the forum but I am not allowed to talk, I keep getting a message that says, you have no privileges yet.
This is copy and paste from DIY Audio.
Don't try to calculate. Inductance will depend on many parameters. Some of these parameters are easy to determine (cross-section, magnetic path length), but others not so (mu, stacking factor, effective gap). Furthermore, inductance depends much on frequency and AC voltage amplitude. So, wind a test winding and measure it under your specific conditions.
You can use whatever number of turns you find convenient for testing. I regularly use 10 turns, as it makes calculations easy and straightforward.
The level of excitation depends on your application, and your test should match it for a good accuracy: an incorrect level could cause a near 1:10 error ratio.
L =( 1.257*mu*N^2*Ae)*10^-8/Lm
where,
N^2 is the squared number of turns, mu is the effective permeability (I suggest using the small signal permeability for SE application which usually spans from 200 to 450 otherwise for PP use 1500 for small signal to 5000 for max value, with minimal gap), Ae is the effective core cross-section (measure the inner core surface and multiply by the stacking factor of 0.95) in square cm, Lm is the average magnetic path length in cm which you can compute by taking the nominal size of the lamination (it's the width of the centre leg of the E) and multiply by 6. The factor 10^-8 will give you the result in Henry.
Wound 500 turns and measured inductance. If inductance = 7H. Plugging that in gives mu = 4690 which would be close to expected results.
Audio transformers are undistinguishable from power trafos. Apply the same math using the lowest frequency you want the trafo be able to pass and the desired induction. When unknown data, I use 8000 gauss or 0.8T (the same). Use the AC RMS voltage at the primary. And in case of DC premagnetization, don't worry. You can test and adjust gap it in situ.
The issue with this bobbin with separate space for primary and secondary will be the increased leackage inductance. IMO I would wound 1/4 pri in each semi-bobbin (let me create a neologism). Thus, 1/2 secondary in each sector after isolation, and thus, end with 1/4 pri in each them.
This wise you mantain toguether low leackage inductance and low capacitance.
This trafo reused core from verical deflection and perform ultralinear using ECL85 pentode without issues.
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This reminds me when I worked at the transformer factory the engineer had 3 transformers made. Next day he tested all 3 transformers then threw all 3 in the trash. He had 2 more transformers made and tested them. Then they ordered a production run of 500 transformers.
What are these math symbols? ^ *
Arrow up = ?
* = ?
I think / is divide?
What is mu?
What is the formula for mu?