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Posted: Thu May 24, 2018 5:41 pm
by Retsel
Hi Stephie,

I would like to build an OTL amp to see what the OTL hype is all about. After reviewing different designs, I think I like your 6AS7 design the best. The great thing about inverted tubes is that they don't require as many tubes, and don't use as much electricity that would heat up the room. The 5687 version does require a lot of tubes, which puts me off some. I figure that with 15 ohm Lowthers in front conical horns handling 500 hz and up, that 3 6AS7 tubes per side would be adequate. I probably would put in and wire up one or two more tube bases (potential for 5 per side) to have extra reserve, and lower output impedance.

Did you ever build the 6AS7 OTL amp, and if so, how did it sound?


You already answered my question

Posted: Fri May 25, 2018 8:00 pm
by Retsel
Never mind about my question. Back in 2011, you commented on the merits of different OTL designs, that the inverted 6AS7 SE amp was not as good sounding as the 5687 amp.

It is interesting that in your writeup about inverted tubes, you mentioned that the EL 509 might be a good tube for an inverted tube OTL amp.

Did you develop the inverted tube plots for the 6AS9 and 5687 tubes, or did you find that information somewhere? I am asking because if I was to try out the EL509 tube, I would might have to do some testing first.