output transformer primary impeadance

[lumox0013]

hey fellas, can some one tell me what the primary impeadance would be when using a 4k -16 ohm output transformer in a single ended configuration by ignoring the center tap. thanxxx

[martin manning]

4k:16, since pp transformer impedances are quoted plate-to-plate. A pp transformer is not made for single-ended use though.

[frankdrebin]

4k:16, since pp transformer impedances are quoted plate-to-plate. A pp transformer is not made for single-ended use though.

there is a way,its called parafeed,then you could use anything even a toroidal.

[tubeswell]

hey fellas, can some one tell me what the primary impeadance would be when using a 4k -16 ohm output transformer in a single ended configuration by ignoring the center tap. thanxxx

A PP OT has one half of the primary winding wound with the turns going in the opposite direction to the other half of the primary winding (because it’s designed to work with AC in opposite phase in each primary half going into a single phase in the secondary). So it won’t work very well if you try and run one AC phase across the whole primary winding for SE. However, you could use one half of the primary winding tho (and leave the other half of the primary floating (or just idling with DC through it). This will result in half of the Pr:Sec turns ratio (of what the nominal PP turns ratio is). As the impedance ratio is the square of the turns ratio, then the SE impedance ratio will be 1/4 of what the nominal PP impedance ratio is.

So if your PP OT plate-to-plate load was 4k with a 16R speaker (an impedance ratio of 250:1), then 1/4 x 250:1 = 62.5:1, so you would need a 64R speaker to get a 4K load reflected across the one half of the Primary winding that you use for your SE power amp.

[martin manning]

A PP OT has one half of the primary winding wound with the turns going in the opposite direction to the other half of the primary winding (because it’s designed to work with AC in opposite phase in each primary half going into a single phase in the secondary). So it won’t work very well if you try and run one AC phase across the whole primary winding for SE.

The primary turns are all in the same direction, it's the current that runs in the opposite way. The problem is that PP OT's are not designed for the high zero-signal flux that is present in a SE configuration.

[tubeswell]

The turn phase is opposite in each half of the primary. It has to be, because the current phase is opposite in each half of the primary, yet in the same phase in the secondary. The only way it can do this is if the turns on one half of the primary go in the opposite direction to the other half. (Think about bucking transformers).

[martin manning]

The turn phase is opposite in each half of the primary. It has to be, because the current phase is opposite in each half of the primary, yet in the same phase in the secondary. The only way it can do this is if the turns on one half of the primary go in the opposite direction to the other half. (Think about bucking transformers).

Put AC into the secondary of an OT and you can measure AC plate-to-plate on the primary. If the two halves of the primary were out of phase they would cancel.

[lumox0013]

thank you for the help , I have some scrap pile transformers that are too small for any thing but a champ or micro amp . maybe ill find some suitable tubes for a push pull amp . i wanted too use them to build a champ and ran across this statement.


Using the push pull transformers instead of a single end transformer is permissible in the cheap output transformers that are intended for guitar amps. The fancy ultra linear expensive transformers intended for high quality audio systems won’t work well if you ignore the center tap, but guitar amp push-pull transformers are just simple transformers with a center tap added. The rated impedance is usually for an 8 ohm speaker as seen by either half of the tube side – that is from the center tap to either end. So if you tape off the center tap the voltage ratio is doubled, but the impedance is 4 times the impedance of either end. A deluxe transformer now sees 26,000 ohms when hooked up to an 8 ohm speaker. This is way too high. You want to get it back to the 6500 ohm range for a tweed amp

but im a simple fella and the math was throwing me ,

[tubeswell]

Put AC into the secondary of an OT and you can measure AC plate-to-plate on the primary.

Yes they do, but on the scope the two primary ends will be in opposite phase. While one winding end peaks, the other winding end troughs, yet the phase being sourced from on the secondary is the same. The only way this can happen is if the primary turns are going in opposite directions. Starting from the CT, you have to wind clockwise for one winding half and counterclockwise for the other winding half. If the primary winding halves were going in the same rotation, the phase on both ends of the primary would be the same (as if there were two identical parallel windings)

[wpaulvogel]

I’ve never wound a transformer. I don’t have any desire. I have watched videos of winding output transformers and they never turn the core around or wind in reverse. I don’t want to start an argument but I’m pretty sure the primary is all wound in the same direction. Once half of the primary is wound, they pull off the center tap, then go back to winding, same direction.

[Ten Over]

The turn phase is opposite in each half of the primary. It has to be, because the current phase is opposite in each half of the primary, yet in the same phase in the secondary. The only way it can do this is if the turns on one half of the primary go in the opposite direction to the other half. (Think about bucking transformers).

tubeswell!!! Somebody has hacked your account.

[tubeswell]

I’m pretty sure the primary is all wound in the same direction. Once half of the primary is wound, they pull off the center tap, then go back to winding, same direction.

Yep that’s looking at the winding from another direction.

[lumox0013]

any suggestions for a micro push pull with those values ? thanxx

[Ten Over]

... to build a champ and ran across this statement.

Using the push pull transformers instead of a single end transformer is permissible in the cheap output transformers that are intended for guitar amps. The fancy ultra linear expensive transformers intended for high quality audio systems won’t work well if you ignore the center tap, but guitar amp push-pull transformers are just simple transformers with a center tap added. The rated impedance is usually for an 8 ohm speaker as seen by either half of the tube side – that is from the center tap to either end. So if you tape off the center tap the voltage ratio is doubled, but the impedance is 4 times the impedance of either end. A deluxe transformer now sees 26,000 ohms when hooked up to an 8 ohm speaker. This is way too high. You want to get it back to the 6500 ohm range for a tweed amp

This guy doesn't know what he is talking about. martin manning does know what he is talking about.

Look at the Hammond 1750H for a Deluxe. It only has two windings on it. There are 28.72 primary winding turns for every secondary winding turn. The primary winding has a center tap, which tells you that the primary is one continuous winding and that the total primary winding has 28.72 times more turns than the secondary winding. Whether you hook this up push-pull or use the entire primary for single-ended, the turns ratio is still 28.72 : 1 and the impedance ratio is still 6600 : 8.

Single ended transformers have an air gap to deal with the constant DC going through them and push-pulls don't. The push-pull transformer will work for single-ended, but not very well.

Hammond 1750H Deluxe.png

[tubeswell]

I’m sorry Martin. I was wrong and got current phase confused with turns direction. I must be suffering from some kind of mental fatigue.