Sunday, March 24, 2019

S5 Electronics "L" series tube amps

In 2009, I started with a Model 8LS stereo amp from S5 electronics.

Model 8LS uses a 5670 double triode as the voltage amplifier and phase splitter and two 6005 pentodes in the PP output stage. (S5 doesn't make the schematic public, so I won't publish it here. Should you want a look, search for it online.)

Initially I built it on a wooden plank as suggested by the manual but later moved it into a Hammond enclosure and replaced the transformers with Edcors (XPWR085 for power and two GXPP10-10K for outputs).

Separately, I built a Model 16LS, which is the same thing with a doubled output stage (four 6005) but the same output transformers as in the 8LS.

Both versions are very easy to build, nice with vocals, but not quite HiFi - see the FFT charts.

Matching (preferably curve matching) output tubes helps a lot with reducing distortion - helps way more than replacing the transformers or the electrolytic capacitors in the power supply! One can get these pentodes in matched pairs and quads from eBay; 6AQ5 or EL90 are other names for the 6005. Also, I am guessing that fine tuning the phase splitter and the screen grid voltage would improve the distortion a bit, although is requires at a minimum a sound card and an appropriate software such as the Arta.








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