cap upgrades are easy and probably make the most improvement, although these kits are now shipping with Solen caps in most locations, only using 715P types in the phono RIAA section, I'll be researching upgrades for those for better matching and performance.
SS rectification is NOT recommended, I could write tons on what I've learned and listened to over the past few years, but in a tube preamp, you WANT a tube rectifier.
None of the voltages in the SP6 are regulated, and they are designed to work with the PAS211 or PA522 power transformer, any substituions here would change the voltages at all points in the circuit, and the series resistors in both the filament circuit and the B+ circuit were optimized to use the PAS power transformer. Same with the power supply capacitors, there is a reason the first 2 are 22uF and the rest are 33uF, although I have a new source of caps that would allow those 33uF to be upgraded to 47uF.
For a volume pot I would recommend as a minimum either the Blue Alps OR the Black Noble. I have both available.
I also have a very nice chinese clone of the $175 Goldpoint 24 step attenuator I can sell for $35.
In my experience doing my "ultimate preamp" last year, I found a very nice combination of rotary switches combined with precision resistors gave me the best results and a nice low cost, using one dual rotary selector for master volume and two mono rotary selectors for left/right gain/balance, you can see more info on that here:
Lastly, let me mention that I am currently in the process of putting together a totally regulated power supply that will work with both the stock Dyna PAS3, and with my VTA SP6 kit.
It will include a new toroid transformer and a regulator PCB, total cost will be approximately $100 but I'm not expecting it to be finished until mid or late February due to long lead times with Chinese suppliers.
I will be able to offer this as a test product within a couple weeks (mid-January) if any enthusiastic DIYers would like to do an evaluation for me.
In addition, by using some Chinese suppliers I will be offering a complete chassis kit similar to what I now show for $350 for around $200. This will only be possible by doing production quantities of the SP6 kit rather than just a few at a time as I have for the past 4 years, which is why I have finally started to run a few ads on ebay for the SP6 kit.
More news, I expect to offer a line-only version of the SP6 by the end of January, and offer a basic chassis for under $40 to go with the PCB/kit/tubes/power supply for around $160.
PS - my work schedule doesn't allow me time to visit this forum as often as I should, so feel free to always contact me directly at either of these emails . . .
Last edited by tubes4hifi on Sat Jan 03, 2009 7:45 pm; edited 1 time in total (Reason for editing : replaced Alps for Noble with Alps OR Noble)