Hi. I wonder if i can parallel two se output transformers. In case that this can work what will be the primary and secondary values? For example if the primary of each one is 5k and the secondary is 8 ohm what will be the values after the parallilizing. Also the current that they can handle will be double?
No if you parallilize both primaries and secondaries they will have the same turns ratio and reflect the same load impedance, it's still 8k : 8R. You can now double the current if that suits your tubes better. The inductance is halved so the low end frequency response may be weaker tho probably not noticable. I'd have a small resistance in series with each primary in case of any imbalance, but not sure if that's necessary.
If you series connect the secondaries, leaving the primaries parallized, you will have twice the voltage swinging which for the same load means twice the current, for a fourfold of power. This means the ratio is now 2k into 8ohm.
This is the purpose,to get half the primary and double the current and power. So it suits me ehh?
You only get to double the current (same as before 50mA in each transformer for a total of 100mA). But the turns ratio is the same. So the tubes will see 8kohms on their plates. There will not be any power increase other than the icreased current capacity which must be backed up with either more voltage or lower load impedance if that is to become more power.
Or you could sell them and get some better suited to your purpose....
Yes, indeed. The other thing I was thinking was to series the primaries and parallel the secondaries. I'm wondering if this would suit a 10Y tube which needs over 10K primary. What would that give?
Previous posters are right about getting the same impedance ratio.
But, careful! If the two transformers are IDENTICAL (same brand, same model/part number), you can double the current and use at twice the power output as suggested above.
However, if the transformers are not the exact same brand AND model, it may not, and probably will not work very well. Transformer A might be designed for a different standing anode current to B. So the "workload" won't share equally. A might be designed for different bass cutoff frequency than B. Then they will have different resistances, and neither will the tube anode current split equally, nor will the secondary signal currents balance.
Two transformers may look identical in size and be almost the same in specs, but one might have a different grade of iron to the other. This can cause bass distortion - may or may not be noticeable depending on the circuit.
Two transformers may look identical and be the same physical size, and both be designed for the same impedances, but one might be designed for a higher power level, and the other for deeper bass. Then they won't share the load very well, due to different winding resistances, and you'll get bass distortion.
Keit
But, careful! If the two transformers are IDENTICAL (same brand, same model/part number), you can double the current and use at twice the power output as suggested above.
However, if the transformers are not the exact same brand AND model, it may not, and probably will not work very well. Transformer A might be designed for a different standing anode current to B. So the "workload" won't share equally. A might be designed for different bass cutoff frequency than B. Then they will have different resistances, and neither will the tube anode current split equally, nor will the secondary signal currents balance.
Two transformers may look identical in size and be almost the same in specs, but one might have a different grade of iron to the other. This can cause bass distortion - may or may not be noticeable depending on the circuit.
Two transformers may look identical and be the same physical size, and both be designed for the same impedances, but one might be designed for a higher power level, and the other for deeper bass. Then they won't share the load very well, due to different winding resistances, and you'll get bass distortion.
Keit
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This will seldom be practical, as the increased impedance will require higher HT in order to extract the power output from the tube(s).
Yes, that is correct.
However, thinking about this some more: There is no reason to parallel the anodes. You can have two entirely separate output stages, and only parallel at the grids and at the transformer secondaries.
This has some subtle advantages. Eg as the tubes age, they will be induced to share the load slightly better. And not connecting the anodes together eliminates one cause of parasitic oscillation.
Keit
However, thinking about this some more: There is no reason to parallel the anodes. You can have two entirely separate output stages, and only parallel at the grids and at the transformer secondaries.
This has some subtle advantages. Eg as the tubes age, they will be induced to share the load slightly better. And not connecting the anodes together eliminates one cause of parasitic oscillation.
Keit
I would rather mate one KT88 with its own single OPT and just parallel the secondaries, and feed the grids together from the previous stage.
You could even make it the Dual-SE topology with two SE stages inverted-connected and fed from the _balanced_ input/driver stage. That Broskie article is about it, no further details though. I tried this in the past but recently realized that the driver stage was not optimal, so I'm gonna breadboard DSE again, and, actually with KT88 this time.
This may be worth a go with a 10Y. It says 10w plate dissipation so maybe 300v at 30mA and -10v or 350v at 25mA and -20v. Trouble is that just gives 9w dissipation which i can get from a 4P1L at far less hassle and into a single LL1682. I could pair up the 10Ys into a single LL1682 but I don't know if I want to sink four 10Ys into something like this.
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