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Old 24th June 2011, 10:28 PM   #11
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Quote:
Originally Posted by bigwill View Post
That's the longest transformer I've ever seen
Indeed. I assume this is a single ended amp? Otherwise I can't see a reason for such a large transformer on an amp that makes "only" sixty watts.
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Old 25th June 2011, 05:13 PM   #12
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The whole thing was overkill! I was thinking less wire resistance with a bigger one, but this kinda got out of hand! I don't think I gained much. One half the size would have worked fine. These should have been used for an amp that put out 120 watts a channel. Great boat anchor!
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Old 26th June 2011, 05:28 AM   #13
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re: transformers....

commercial transformers are built with profit in mind......DIY'er transformers need not be like that......
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Old 27th June 2011, 04:16 PM   #14
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Totally done!
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Old 16th July 2012, 08:32 AM   #15
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Nice project, and I hope you won't hurt your back moving them.
A friend of mine is making something similar but he does'nt get the interstage transformer to work. Loss of high freqency or dips at 20 and 40 kHz.
Can you please tell how you wond them?
Thanks,
Steven
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Old 16th July 2012, 03:55 PM   #16
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I meant wound/winded.
steven
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Old 17th July 2012, 05:38 PM   #17
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My back was ruined many years ago. I can still move it but hard for me now. The driver transformers have around 3000 turns on each of the 4 windings. They are wound with the first 2000 turns just spindled on, the last 1000 turns are scramble wound. It is split bobbin. Start of winding is B+ so finish is in the middle. Second coil wound over first is wound in the opposite direction and finish is bias supply. So there are 2 sets of coils. The 2 coil sets are wound in opposite directions. The .1 Uf cap is across the plate and grid connections. No cap and the thing resonates secondary coil at around 1 Kc. No way to eliminate this cap unless the thing is wound bifilar. Or interleaved which is a real pain. I tried it and results weren't that good. Also made it larger to fit in all of the insulation. Bifilar takes triple or quad insulated magnet wire which seems impossible to get. If this is confusing, I can draw up diagram of it. Seems expensive commercially made ones also use the added capacitor.
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Old 28th July 2012, 10:36 AM   #18
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It is clear that these transformers always are heavy and expensive because they are difficult to make. We tried bifilar but that didn't work either. I wish some guru told me how to wind something like this. Interleaving also didnt do the trick.
Next try might be a 4 division bobbin, as few layers as possible but 'heaping up" the wire to minimize capacitance, B+ in the middle, bias at the outside so cold ends of the windings are close to the core and hot ends are close together. We'll see.
This is meant for an ECC99 driving 6528.
Steven
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Old 28th July 2012, 10:40 AM   #19
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you can use the search button and look for postings by YvesM, BudP, cerrem, smoking-amp among others, lots of good information in their posts...
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Old 28th July 2012, 02:23 PM   #20
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The reason for the high freq. oscillation is two fold a .6 pf plate to plate capacitance and stated min grid stop is 500 ohm pre grid . By swapping section in the tubes the coupling is inverted braking the loop gain that made it oscillate . the transformer load may well provide the grid stop load need. Sorry if I came lat to the party . Where are you finding 6528 at a reasonable price ? Given the coated graphite plates if keep under 30 watts will last a very very long time.
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