Tweaking Cary SLP-98P F1 Preamp

As you know for SLP-98, the F1 mod is a significant improvement over the standard. I just bought one used and the stock 6SN7 tubes that come with it are horrible. So, I am waiting for WE6SN7 tubes for it. Until it arrives I want to ask people with experience with F1. I have Pass X350.5 amp driving Soundlab ESL speakers.

1. How good can it get with best tubes?
2. Some have recommended using NOS 6f8g/adapter instead of 6SN7, any thoughts?
3. After getting the best tubes, is it still worth it to direct-couple it? It is supposed to improve bass, dynamics....
I’ve been amazed by the improvements I have gained through using Symposium Rollerblock Jr’s under my VAC tube preamp. I think the Cary preamp will benefit as well speaking as a former SLP-98P owner (not F1). My Cary came across a bit lush and lacking a bit of detail and air. The Rollerblocks really improve these aspects.
You put them under the chassis.  I have not used EVP blocks but I have compared the Rollerblock Jr's to BDR cones/pads, Isoacoustics Orea's, and Golden Sound ceramic cones.  Rollerblocks were clear winner in every case.  Plus they aren't terribly expensive (compared many other products) at $225 for 3.
I have a Cary SLP-98 F1 in my big system. I have not rolled any tubes yet. It's not the last word in pre-amps but it is still a very good pre-amp with some musical leanings. It should work well in your system but if you are looking for more accuracy and perhaps more detail a top of the line Audio Research will push you in that direction. I personally like the sound of my SLP-98 and don't have any plans to replace it.  
...I personally like the sound of my SLP-98 and don't have any plans to replace it.  
Me too. Nice outboard power supply, and with top shelf 6SN7s, upgraded coupling caps and rear wiring, using quality OCC interconnects, performs as well as I'll ever need.    
Hi chungjh

With so many vintage 6SN7 nos tubes out there, why mess around with adaptors. There are a lot of people that feel that the 6SN7 is one of the best sounding audio tubes ever made for a preamplifier. I’m sure if you spend the money and find a reputable dealer you can trust who tests his tubes and properly matches the tubes that the sound quality will amaze you when compared to the factory tubes. I would recommend the better name brands from the 1950’s or the 1960’s. When you start getting into the middle to later  1970’s the quality starts to drop off. I would focus on the better name brands like Telefunken, Amperex, Siemens, or Mullard. These can be expensive but they can absolutely transform a preamp’s sound quality to a whole new level. Try Brent Jessee’s website.  For an extra $10.00 a tube he will properly match them with a curve tracer which is a piece of equipment a lot of these other tube dealers don’t have. I would recommend tubes with the same name brand, made in the same year and with the same date codes. Once you hear a great pair of properly matched, nos vintage tubes, you’ll never go back to using the factory tubes! Good luck. 

Has anyone direct coupled their SLP98F1? I sent mine down to Cary for direct coupling. I used to think direct coupling meant removing the output capacitor, but it sounds like Cary takes out capacitors between the gain stages. Is this correct?

Not that much. I ended up selling it. I am now using Benchmark LA4, which is great.