Have anyone tried to use an OPT with multiple primary impedance taps?
Not for UL operation, but for regular anode connection.
Imagine we have a 4 sections OPT, like this
P:S:S:S
(Primary section, series wired)
(S:secondary section, series or parallel wired)
Imagine the primary impedance is 5000 ohm (for EL84 or 6V6)
If we make a primary tap at the beginning of the last primary section:
B+ --- P:S:S:S( here )P --- anode
We will get around 2.8 kohm impedance, if moving the anode there.
Suitable for paralleled EL84/6V6 or even for single EL84/6V6 triode mode.
The idea is using the full primary, OR using the shortened primary, leaving out the last section, to be able to use in other configurations such as those I just mentioned.
I suppose it will work perfectly fine, as winding sectionalization is still ok, and leakage inductance shouldn't suffer.
What do you think?
Not for UL operation, but for regular anode connection.
Imagine we have a 4 sections OPT, like this
P:S:S:S
(Primary section, series wired)
(S:secondary section, series or parallel wired)
Imagine the primary impedance is 5000 ohm (for EL84 or 6V6)
If we make a primary tap at the beginning of the last primary section:
B+ --- P:S:S:S( here )P --- anode
We will get around 2.8 kohm impedance, if moving the anode there.
Suitable for paralleled EL84/6V6 or even for single EL84/6V6 triode mode.
The idea is using the full primary, OR using the shortened primary, leaving out the last section, to be able to use in other configurations such as those I just mentioned.
I suppose it will work perfectly fine, as winding sectionalization is still ok, and leakage inductance shouldn't suffer.
What do you think?
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I was thinking that, usually first and last sections are half of a regular section. This is suggested to improve (reduce) leakage.
If we leave out the last section, then we have a non symmetrical transformer.
We will go from:
B+ --- p : S:S:S : p --- anode
(p: half turns primary section)
to:
B+ --- p:S:S:S --- anode
Not ideal, I suppose.
If we leave out the last section, then we have a non symmetrical transformer.
We will go from:
B+ --- p : S:S:S : p --- anode
(p: half turns primary section)
to:
B+ --- p:S:S:S --- anode
Not ideal, I suppose.
No, you must keep it symmetrical.
Hey, here you have one such "universal" transformer, designed for Hi Fi but which was famously used by Marshall to build their first amplifier:
http://www.mercurymagnetics.com/images/transformers/schematics/OT/O45RS-L.pdf
Hey, here you have one such "universal" transformer, designed for Hi Fi but which was famously used by Marshall to build their first amplifier:
http://www.mercurymagnetics.com/images/transformers/schematics/OT/O45RS-L.pdf
That transformer is push-pull. Easy to keep symmetrical.No, you must keep it symmetrical.
http://www.mercurymagnetics.com/images/transformers/schematics/OT/O45RS-L.pdf
Yvesm, paralleling sections of lots of turns is something I avoid, because theoretically, both sections MUST be exactly equal turns. This is difficult when there're hundreds of turns.
Menno van der Veen has a thing going called "The Project" where he uses transformers designed for multiple applications. Well worth a read.
Menno van der Veen, audio electronic research & consultancy
Menno van der Veen, audio electronic research & consultancy
Very interesting.Menno van der Veen has a thing going called "The Project"
For example, he uses a push-pull OPT for SE too, by leaving another tube (as if they worked in push-pull) as current source (no signal input, just bias) to keep the OPT happy, so it does not saturate.
If it were me, I'd replace the second tube with some other solid state current source.
A slight digression on the starting topic.
Nice way to reuse PP OPT, or to wind a multi-functional OPT as Menno does. Or even, wind a PP from the begining to be used as SE, to avoid gapping, and achieve higher inductance.
The VDV-GIT80 OPT used for "The Project" still requires DC compensation for SE operation. Using a PP OPT (without airegap) for SE operation is usually not a good idea. More details here: https://mennovanderveen.nl/nl/download/download_3.pdf
Yes jazbo8, as I said in my previous post, for SE operation, "leaving another tube (as if they worked in push-pull) as current source to keep the OPT happy, so it does not saturate."
I just find it much more efficient to use a solid state current source for these, rather than leaving a hot tube "idle".
Thanks for the link to the paper.
Going back to the matter
I designed a low power SE OPT like this:
(p: half turns primary section)
B+ --- p : S:S : p : p --- anode
It taking the output from a tap between those last primary sections:
B+ --- p : S:S : p --- anode
I get some less inductance, and I'm able to suit better UL-triode modes, than just add a switch (to connect either UL tap or anode via a 100 ohm resistor to the screen) and use the same impedance, as many people do (which is just unfair for comparisons).
I suppose the leakage inductance will not be much worse.
Any alternatives to this?
How would you do it?
I just find it much more efficient to use a solid state current source for these, rather than leaving a hot tube "idle".
Thanks for the link to the paper.
Going back to the matter
I designed a low power SE OPT like this:
(p: half turns primary section)
B+ --- p : S:S : p : p --- anode
It taking the output from a tap between those last primary sections:
B+ --- p : S:S : p --- anode
I get some less inductance, and I'm able to suit better UL-triode modes, than just add a switch (to connect either UL tap or anode via a 100 ohm resistor to the screen) and use the same impedance, as many people do (which is just unfair for comparisons).
I suppose the leakage inductance will not be much worse.
Any alternatives to this?
How would you do it?
Sure.
In this particular case, the full primary is used for UL operation.
Leaving the last primary section out is for triode operation.
I thought that triodes strapped pentodes, due to their low output impedance, would requiere less primary inductance, and probably it will work just fine.
In this particular case, the full primary is used for UL operation.
Leaving the last primary section out is for triode operation.
I thought that triodes strapped pentodes, due to their low output impedance, would requiere less primary inductance, and probably it will work just fine.
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