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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

How can I check if my Boyuu O.T. has airgap?

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If you use a moving coil meter, AVO 8 etc, when on low Ohms range you measure the anode winding resistance, it should give a reading far faster reading if there is an air gap, than not.
Compare the time it takes for the needle to settle with a mains transformer.
That will give you a reasonable indication as the air gap stops the saturation build up faster than a non air gap transformer.
You likely don't know if the OT has stamped E-I style laminated core, or a toroid ?

Are you concerned about some performance aspect of your amp, or just curious ?

A youtube vid shows each channel is single-ended, so the output transformer by design has to manage a DC level - which is typically achieved by designing in an effective air-gap (that may be a single gap, or multiple gaps, or achieved through grouping laminations).

You can measure the primary winding inductance for varying DC current out to at least double the EL34 bias current - see link.
1. Line up all the E laminations on one side of the coils, and then line up all the I laminations on the other side of the coils, and then place paper or other thin material between the laminations (the "air gap"). That is an SE transformer.
Takes DC real well.

2. Interleave the E laminations (E one direction, then E the other direction, alternating back and forth, back and forth, through the coils) and put an I lamination at the end of each E lamination, one by one. That is a Push Pull transformer.

Pretend you are in charge of producing the output transformer for the Boyuu.
Which one will save labor ($$$)?
#1 or #2?

Pretend you are the producer and seller of the complete Boyuu kit.
Would you be willing to use output transformers that did Not have an air gap?
Do you care about customer reviews?
Do you care about customer returns?
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> Interleave the E laminations..., alternating back and forth, back and forth, ...put an I lamination .., one by one.

FWIW: there is a machine to do this snik-snak fast, and for the ordinary sizes it is shockingly inexpensive. Even with low-pay labor and modest production, it makes a lot of sense.

But yeah, the gap core is still less time/labor. (A GOOD gap core is actually a lot of work to line-up the lam ends exactly flat, but I don't think most winders bother.)
1. Just a little story:
Maybe a company ordered way to many push pull transformers, and could not sell enough push pull amplifiers to put them in.
So they decided to sell single ended amplifiers and use the 'extra' push pull transformers. They very carefully cut the center tap extremely close to the transformer body (look for that extra wire). You can not find it? (that is because they did not do that).

No, I doubt any of those kit SE amplifiers use Push Pull output transformers.
What they do use is: SE transformers that do not have enough laminations to go down to full power at 20 Hz.
Please stop worrying and enjoy the amplifier.
Are you concerned about some performance aspect of your amp, or just curious [/URL]

The amplifier works ok (sounds good) and I have replaced nearly all the circuitry with a new design of mine.

Now I'm just thinking if or not to improve and replace also the original OT. Today I have removed it to see how are oriented the laminations... but it is fully impregnated with resin..... No way to understand.


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