What is the purpose of the triode switch for the Hyper modified ST70? Is it a better setting?
reactions are mixed on the use of the triode switch...some like it some don't...some find the triode mode sweeter and mellower in sound at the expense of some dynamics. you also lose out power. i personally prefer the orig penthode, so it's a matter of personal taste
Hi guys!
Just a comment on triode/pentode EL34 operation. I hope when an A/B test between triode EL34 and pentode EL34 is conducted, negative feedback [NFB] is optimized for those two different applications because comparing a triode'd EL34 to a pentode EL34 with pentode optimized NFB is like comparing apples and oranges.
Typically, pentode PP amps have anywhere between 10-20dB of NFB. Merely installing a switch to connect the screen grid to the plate of an EL34 does not guarantee optimized performance for triode configuration because a triode connected EL34 needs much less NFB. 5-7dB of NFB is sufficient to linearize its performance. With 20dB of NFB on a triode EL34, the amp will compress dynamics and constrict the midrange.
Also in terms of actual power, 35W [pentode UL] vs. 15W [triode] isn't really much of a difference in the real world of audio. An optimized triode'd EL34 can actually "sound louder" than in pentode mode because clipping will be softer and distortion will be mostly even order harmonics which are most pleasant to the ears. Scientifically power [watts] and sound pressure levels are logarithmic but the human ear is linear. That's why IMHO the "first watt" always counts in the world of tube amps because who would want a 60W amp wherein the non-linear distortion will just rise exponentially?
May or may not be true but someone once told me that tube life may be shorter in triode mode. Guess the guru's can explain if it were true and how/why so.
That depends, if the B+ voltage on the plate does not exceed the maximum rating of the screen grid [as per tube manual specs on an EL34], then maximum life will not be affected.
Regards,
JE