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Old 6th August 2007, 11:07 PM   #1
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Default SE Trafo for PP use

Just for the sake of having something to experiment with, is there any reason not to connect two single ended transformers in series for use as a push pull transformer?
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Old 6th August 2007, 11:22 PM   #2
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When you accept that,

-you need output 2 trannies per channel (doubles the weight & cost)
-DC will NOT cancel anymore (need of large core & airgap)

, then there's no reason why you shouldn't do it
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Old 6th August 2007, 11:54 PM   #3
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Quote:
Originally posted by the_manta
When you accept that,

-you need output 2 trannies per channel (doubles the weight & cost)
-DC will NOT cancel anymore (need of large core & airgap)

, then there's no reason why you shouldn't do it
And the power won't be the square of the tubes, minus losses anymore ... they'll just be paralleled SE tubes.
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Old 7th August 2007, 12:16 AM   #4
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All of that is fine -- this is just for some bread board experimenting. Thanks.
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Old 7th August 2007, 12:30 AM   #5
PeteN is offline PeteN  United Kingdom
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Surely the lack of magnetic coupling (well, tiny amount) between the two trafos will prevent the push-pull from working, due to the way voltage is induced in the "off" half of the primary by the magnetics caused by the "on" half?
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Old 7th August 2007, 01:33 AM   #6
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by PeteN
Surely the lack of magnetic coupling (well, tiny amount) between the two trafos will prevent the push-pull from working, due to the way voltage is induced in the "off" half of the primary by the magnetics caused by the "on" half?
This really only matters if operating class B, I doubt it matters at all with what I wil call "summed anti-phase SE" for the lack of a better term. I think about power will be about equivalent to a pair of SE in parallel, possible the even harmonic cancellation of PP would be retained.. (I haven't thought about this.)
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Old 7th August 2007, 02:30 AM   #7
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I absolutely agree with Kevin in that the even harmonics will still sum and by nature of them being out of phase they will appear to cancel. As he mentioned this is only the case for pure class A operation and once you near class B the coupling of the windings via core and proximity becomes a much different situation. That said, it only makes sense to me that a transformer wound for class A has different needs than one wound for AB just as a transformer wound for a triode has different needs than one wound for a pentode.

I say go for it and report back. If you already have the parts on hand in a junkbox what do you have to lose? If you purchase them and the project is deemed a failure, you now have a really cool junkbox for future builds.

dave
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Old 7th August 2007, 02:32 AM   #8
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The issue is that I built this circuit ...

Click the image to open in full size.

... and it doesn't work at all. Total floparoo. Well, it amplifies the signal, but the noise is louder than the output. I was super careful with grounding, the heaters are regulated DC, the B+ supply's ripple is in the uV range before the CCSs, and the PS is a long way away. I also tried lots of different tubes, but no improvement at all.

So, I thought I'd back up a step. I have built lots of single ended parafeed linestages. Now the plan is to buid two of them, get them working individually, then put them together to see if I can track down the issue, then swap in the single output transformer -- unless someone sees an error in the schematic.
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Old 7th August 2007, 02:34 AM   #9
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Quote:
Originally posted by dave slagle
If you purchase them and the project is deemed a failure, you now have a really cool junkbox for future builds.
If the definition of junkbox is leftover parts purchased for failed projects, mine is impressive enough already
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Old 7th August 2007, 03:57 AM   #10
kevinkr is offline kevinkr  United States
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Hi Doug,
What kind of noise? I don't see anything inherently wrong with this design on a quick inspection. Are you sure something is not oscillating- often vhf oscillations will manifest as odd hums and buzzes.. (and other things) Could be the ccs oscillating too.

You mention the power supply is a long, long way away - any local supply decoupling? You might be surprised at what the supply side of a ccs might do if presented with something other than a low rf source impedance..
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