martin manning wrote: ↑Sun Apr 07, 2024 12:46 pm
Do you have a known good set of tubes in this? Those voltages came from my LTspice simulation, so they are "perfect" specimens.
OK, I rolled a number (5 or 6) of tubes through V1 (5 or 6) and they were all about the same. I left in the one that seemed to sound the best to me and that also gave me the highest Cathode Voltage of about 1.5V (so they were al pretty similar).
I reinstalled the LNFB on V1 with the 3 position switch and went back to the single input underneath the switch (since a low input is ridiculous with how clean this amp is already). I do think the LNFB switch does help take the edge off and round off the attack of the note a little bit while maintaining the same clean sustain, so I guess that is a step in the right direction. I didn't have the 10M resisters, so I used my last couple 8.2M resisters, and then 2x 4.7M (9.4M) resisters for the one that connects to the second stage grid.
20240408_165301.jpg
Speaking of the cleanliness of these SSS amps, how clean do most peoples' SSS amps stay throughout their volume pot (without FET input)?
I removed the 20K dropping resister and brought it back down to a little more reasonable 13.6K (2x 6.8K in series). This helps keep the V1 and V2 plates at about 188VDCish while the PI plates are at about 235V.
It just occurred to me that I should roll some tubes through V2 as well, and see if that one is affecting things. I'll try that next. I'm a little reluctant to start changing cathode resister values since it seems that all iterations of SSS models stay at 1.5K throughout with mostly 4.7uF bypass caps. I may have chosen the wrong version of SSS to mostly follow but I've definitely heard some models of SSS amps of uncertain lineage, that have that special bloom and sustain that I am looking for. (I'll try to find the youtube samples of the ones that get what I'm after)
I see a schematic of #002 with added 100R resisters. Can anyone explain what those are going for?
OK, I'm going to roll some tubes through V2 and then I ought to tackle the PI balance method next.
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