Hi, probably a am a little late on that chat, but I have just started a new project OTL-ESL 63, taking in account Tim's otl design as it is and my ESL'63. My intention is to swich the primary trafo of the 63 from 8 ohms(16+16 paralel is original) to 32 ohns, puting the two coils in series. More than that, as there is room on the input trafo I think to duplicate the primary and all together to go to 64 ohms. Am I crazy? (now I am gatherin the components, including 4 trafo from an desasenbled esl 63 to be modified. what do you think about?
Go for 32 ohms- that will make your amplifier fairly easy to build. It will get trickier as you try to go to higher impedances.
Combination with Magnepan and Zero
I build Tims OTL last year and combined it with my (modified) Maggies (MG12). I ordered two Zero's from the states and determined over ARTA and my ears the best combination. Because I don't need the maximum power the OTL can provide (I got neighbor’s!) I finally used the 3X tab as optimum, resulting in an Ohmic load between 8,2 Ohm at 115 Hz and 13,8 Ohm at 20KHz. Because I combined the Maggie with a parallel woofer, I had to use an RLC impedance correction network at 730 Hz (see attachment).
I build Tims OTL last year and combined it with my (modified) Maggies (MG12). I ordered two Zero's from the states and determined over ARTA and my ears the best combination. Because I don't need the maximum power the OTL can provide (I got neighbor’s!) I finally used the 3X tab as optimum, resulting in an Ohmic load between 8,2 Ohm at 115 Hz and 13,8 Ohm at 20KHz. Because I combined the Maggie with a parallel woofer, I had to use an RLC impedance correction network at 730 Hz (see attachment).
More recently, I am stressed by the idea of finding a better tube instead of ef86 in my scheme. That's because over time, the only problem was the premature wear of the two pentodes, which can lead to a collapse when the power tubes remain without bias. I noticed that one of the two pentodes works at the limit in Tim's scheme which can cause wear. What can you suggest?