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In Reply to: RE: Not according to the Eico schematic posted by Triode_Kingdom on June 12, 2017 at 11:11:51
I was just in there yesterday, but maybe i did not remember the filament circuit going from the rectifier to other tubes. Anyway it was mostly a mental exercise as it turns out. I have pretty much nixed that idea.
The schematic does have errors in it and frequently EICO would make running changes to the circuit without updating the schematic. For example, on my copy of the owner manual the filament circuit is biased with positive dcv from the last tap of the B+ supply. the 2 resistors used are 100k and 27k But it appears that the schematic has the 27k as the dropping resistor and 100k to ground. This, is opposite to what it should be, but if you check the schematic one would think that is how the resistors are labelled. thanks for the support, Dak
So, maybe the Eico schematic I saw was somewhat preliminary, and they changed it later. About your original question, I don't think it's worth the trouble VS buying the 6X4. If you decide to pursue it, some of the 12V switchers on eBay are very small and inexpensive. The output can be left floating (ungrounded), so this might be a much less painful way to heat the 12X4.
Buy Chinese. Bury freedom.
Yeah, i was just brainstorming some ideas to get around the bump in the road. And if it was feasible to do the voltage doubler circuit, which had the potential to yield additional benefits, besides allowing the use of my 12x4 tubes, i would have pursued that. But as you and others pointed out the EICO tranny is probably not capable of doing such a conversion.
You mentioned about using low voltage SS power supply for powering the filaments and i am intrigued about that. I need to rebuild anohter vintage preamp that i have postponed for over 10 years and i think using something like that would be a neat way to make the rebuild more in line with current trends. cheers.
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