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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: RE: Alex... posted by Al Noakes on October 27, 2014 at 14:25:07:
A 10A filament will need a 160W transformer. You'll need to remove turns from the secondary of the output transformer to reduce it to 5V. You might also want to install a couple low value resistors to "trim" the final value (that's what I do in my 211 SETs).
I searched eBay for "160W electronic transformer" while writing this and came up with quite a few hits for 120V and 220V versions. Unfortunately, none of the listings show the inner workings, so there's no way to be certain if the output transformers are toroidal. On the other hand, none of them appear to be potted, so it's a simple matter to pop one apart and look. At worst, you'll lose $15 for your effort.
Just so you know, where Alex and I primarily differ in all this is the operating frequency. Alex is using newer transformers that operate at 30kHz or so out of the box. The transformers I modified years ago are running at 65kHz. Lynn Olson cautioned me at one time regarding the possible side effects of using such a low frequency (65kHz), and although they sound fine to me, I do wish they were operating at 100kHz or more. In fact, if memory serves, Davie Berning's amps use a minimum frequency of 250kHz. I suspect the upper frequency limit of these little transformers is determined by the capacitance of the active devices. Someday I'll revisit this, just to see if they can be made to do better.
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