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This was brought to my attention by an email from a friendly fellow countryman of mine.The advantages are:
No saturation of the core and
a low internal resistance (is that the same as low DCR?)Apparently one can use a secondary of a power tranny
Any thoughts?
Follow Ups:
...this has got me thinking . If I were to use a small 115/115 toroid and unwind the secondary , this would make a very nice differential anode load . 30/50VA toroids usually measure at least 100H . Good for when plenty of volts are required with low HT . Just a thought...FB
it works quite nicely.... give it a try what do you have to lose???as ken said, just remember that the max AC they will like to see assuming perfect DC balance is 120V @ 60hz, which is 60V @ 30hz, 30V @15hz so i would keep this to low level stages to begin with.... the work up in voltage....
if there is a little DC imbalance between the 1/2's then you will reduce the max AC available before saturation.
i find a 25 ohm ww pot between the cathodes of a pair of 6C45's with the wiper connected to a choke with the proper DCR to bias the tube works very well in this situation.
a simple 20hz sinewave and a voltage meter will allow you to adjust the pot for max output which should happen at perfect balance...
a scope will quickly tell you when the choke is saturating... you start seeing a "kink" in the sinewave near the zero crossing.
dave
...just one last thing , Dave . Has that NY Noise event happened yet ?
I'm interested to hear how that crazy amp of yours is doing...FB
its over and done.... the amp is my current bass amp.it sounded suprisingly well fullrange at noise, it was unlistenable on my fronthorns, but works great on the basshorns.
i have to work on it a bit to quiet it down a bit... then possibly design some autoformer outputs.. i'm sure the toroid 1:1's are the limiting factor on the bass... even with the loz Rp of the 6C33... i'll have to keep my eyes out for some 230:230 toroid isolation trannies
dave
it would work, but don't expect to put more than 115vac across the primary--more than that (i'd say around 130) will saturate the core.you could test the max input voltage with a variac and a current meter... with just the primary across the line, slowly increase the input voltage. the large reactance of the winding @ the line frequency will prevent much current from flowing. as you continue to advance the input voltage with the variac, when the current drawn from the line increases greatly you know you have reached the point of saturation, and that represents the max primary voltage that will be tolerated.
ken
Hi Ken,What I don't understand is the voltage part. Is it not current that determines saturation. Or is it the combination of the 2..
Regards,
Bas
its a combination of the two.its AC voltage and DC current that causes the core to saturate.
the more DC current the less room you have for AC voltage.
dave
Hi,On mains, which is more or less unlimited currentwice, a 30% voltage overload would make the flux to "break down" and one has a current rush...
A 2*110V 50Hz will have a larger margin than a 2*110V 60Hz, and a 0/230/480-50Hz would make it :-)mvh /Pär
as well.... as supply for the screen grids..
nt
No satuation but no inductance either! (except for leakage) I like the first circuit - a good way to get lower voltage, a little more current from a transformer (due to improved power factor). I'd use it for class A only, as regulation is poor.
As a post below says, only one half of the choke is operating at a given time.I think there will be a problem with using this arrangement as an input choke, in that the normal function of an input choke is that the magnetic field storage in the core "fills in" the gaps between the current peaks of the input, the critical inductance being the lowest value with enough energy storage to achieve this. In the centre tap arrangement this can't happen because the magnetic flux must reverse direction each half cycle, so it must fall to zero on the way through.
Hey-Hey!!!,
I've been looking at this set up since you posted questions. I think that the half of the transformer winding--CT to leg in question, must have this inductance. THe other side is carrying little if any current to contribute to magnetizing things in the core. Another concern is the DC content, a 'regular' iron cored choke has a substantiol air gap, usually the E's and I's arranged seperately and spaced with some paper. A power trans won't have this air gap and will behave more like a swing choke, high inductance until current flows. This might be a good thing...as the critical inductance increases with decreasing current, the inductance will also increase with less current. I have a 2 kV power trans I am going to experiment on, it is a big one, about 10 kg, I think that the primary should be left open or with BIG resistor actoss it, will try both ways. Any suggestions for experiment set ups?
regards,
Douglas
Hey-Hey!!!,
There is one benefit I can see with this set up. I think that the PIV ratings for the diodes will be very low. I'll walk through a cycle, with Bas' schematic. As the top of the secondary goes high it will begin conducting current, this current will drive the lower half of the choke lower than B+, as the lower secondary is going negative wrt the top one. HTis is the primary reason for this in my book, I think that best use of the 600 PIV schottky diodes can be obtained in this sort of circuit. fewest diodes( two ) and ability to use a standard CT secondary of more than 200 V per side.
good listening,
Douglas
Had an erroneous picture showing the lines after the rectifier to ground....
Very interesting.
the core can and will still saturate.. after all, you aren't passing current through both halves at the same time.ken
off the other on switches on? Make sense to me.. But do they? Or do the switch on at the same time but pass opposite phase. Then it would work just like a push pull tranny.Sorry bout the ignorance... But it's a good way to pick people's minds.
Regard,
Bas
Yes. Each rectifier plate is like a one-way valve. They conduct in one direction and shut off when the voltage crosses zero.Gary Dahl
Below
Shucks, didn't think of that.
...I suppose you're right there , but would it not be dangerous to have the primaries flapping ? I would have thought that the primaries would be connected (higher inductance) with the secondaries flapping or have I got it wrong ?
...FB
Hi fatbottle,Suppose you're right about the primaries flapping posing a hazard. In that case one could just insulate them... And maybe the primaries have less of a current ability. Apparently according to the guy who sent me the idea the secondaries of his center tapped transformer have a rating of about 6H.
Seemed very interesting and so I'd thought I'd post it to find out more.
Apparently this schematic was posted in 1954 and the guy that had sent it to the magazine/book won a pair of output transformers for the idea.
Regards,
Bas
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