If anyone is still looking for a SLP-98

The SLP-98P F1 is a very nice little preamp.  The jaguar red is especially beautiful I always thought. My favorite color on the Cary equipment. 
Cary Audio only used the Jensen oil caps as an upgrade (early oils were Audio 1’s), otherwise it was polypropylene. Eventually moving into the Mondorf’s.  The Jensen oil caps are a bit more laid-back and tame compared to polypropylene’s, which are typically more detailed and airy.  It’s all going to depend on the rest of your system and your taste.  Also polypropylene caps last longer than oil. Oil caps last about 5 to 10 years and may start leaking or dry up.  The leaky issues are more on amps with higher voltages than on the preamps though.  
Hexfred’s I thought we’re great upgrades on these. Upgrading from the standard diodes to the hexfred’s you’ll notice more detail and faster bass. The SLP-98 has always had solid state rectification, which does not mean it’s a hybrid. Hybrid has to do with the actual analog circuit not the power supply.  
The SLP-98P F1 can still be taken a lot further in sound quality with some power supply upgrades and even better coupling caps.  Installing some large10uf polypropylene bypass caps on all the PS electrolytic caps makes a big improvement.  We always used Solan as they are a good size and fit well.  The F1 should have Kimber Kable in it but maybe not.  Upgrading to a good quality wire makes a big difference inside.  The only thing I didn’t like about the Kimber was it’s not shielded and consequently, picked up information from the other inputs wiring if a source was still on. Now days, I’d look at some good shielded OCC wire. 
As for tubes, I always thought JJ was crap. Sorry but just my opinion.  EH are Russian and tend to be a more on the hard/bittle bright side for my taste. Old 6SN7 Sylvania’s are fantastic for detail or RCA for more smooth body.  Also Tungsol, etc. 

There’s not a ton of room inside of the SLP 98P F1.  It’s pretty jammed in there already so there’s not a lot of room for huge upgrades.  Adding the Solen 10uf Polypropylene’s caps will help a lot. 4 in the preamp and a couple in the PS.  And the PS I used to always at a couple of higher quality .22uf propylenes to bypass the Solen’s.  Really makes the power supply cleaner and improves not only imaging and that blacker background but bass improves  

Somebody else mentioned they had an SLP 05. It’s super important to match the gain of the tubes to get correct channel balance.  I used to do this on the bench with a scope and meter but it can be done with just a meter and a signal generator or CD player with a 1K sign wave CD into the single-ended inputs.  There are trim pots inside the unit, which has to be opened up and turned upside down to get to the pots that are mounted on the pc board.  Those trim pots adjust the volume to the rear negative phase tubes.  First make sure the two positive phase tubes are putting out equal gain by measuring the output with the volume control turned all the way up.  Once they’re equal then you adjust the negative phase trim pot to match the volume of the positive phase tube that’s in the front tube socket. You do this for the left side and then the right side until you have all four phases of equal output voltage.  DONT TOUCH THESE TUBES NOW.  LEAVE THEM IN PLACE. Now you move on to the balanced inputs. if your DAC has balanced outputs it’s perfect.  You can play the 1K sign wave into the balanced inputs and swap tubes until you have equal output voltage on all four phases.  Yes there’s a bit to this.  And this is why most people send it in to have it done but you can’t do that every time you want to swap tubes around so hopefully this will help somebody.  When ordering tubes it’s important to ask for tubes that are matched for output/gain.  This will make everything much easier.  Especially for those two front line level positive phase tubes and the two balanced input tubes.  BUT every time you change the line stage tubes (not the balanced input tubes) the negative phase trim pots will always need to be adjusted to match the positive phase tubes, otherwise the negative phase may be louder than the positive phase or way too quiet and not canceling out noise correctly and the volume into your balanced amplifier won’t have the same channel balance.

Thanks guys. You are an absolute wealth of information. I look forward to having the SLP in my system and more discussion to follow. Many thanks.

@harpo75 ,  interesting read on adjusting the trim pots on the SLP-05.  That sounds like it would be a lot of work to roll tubes.  And I guess to perform the procedure the preamp would have to be setting on some type of open support box so that it could be upside down with the tubes installed  and the bottom could be off (as I do not have a tube cage for mine).  I suppose if I was going to do this, the best thing to do would be to buy a tube cage from Cary.

Anyway, as far as this goes

  It’s super important to match the gain of the tubes to get correct channel balance. 

forgive me for this question, but is the bottom line that the goal of this procedure is to get the output the same on  both the left and right sides?

If that is so, here is what I have found with mine:

First of all I am using the balanced inputs, and I have what is literally a plethora of pairs of vintage 6sn7s that I can roll in those sockets.

I have used a test CD with "315 Hz System Setup and Balance Tone" and a voltmeter to check the output of the amp on both the L and R side.  If the balance has not been equal I have found that swapping the phase buffer tubes from side to side has no effect on the readings I have gotten.

BUT, if I swap the balanced input tubes from side to side, I have found that the uneven AC voltage readings follow the (balanced input) tubes.  I've actually found certain pairs of tubes in the balanced input sockets that give me very nearly equal AC voltage readings on both sides.  So if I have nearly equal readings, there should be no need to do anything with the trim pots, correct?

Here is what I have been doing with pairs of balanced input tubes when I am getting unequal readings with my AC vm: 

first I have noted that when I totally defeat one channel and check with  my sound level meter and  that I do not get equal db readings from both side of my room.  Therefore, I put the strong tube on the weaker side of the room. 

Secondly, I have played around with using the L & R "input level" knobs to achieve balanced readings on the AC vm, and after that adjust to achieve equal db readings with the sound level meter. 

And I realize that using the "input level" knobs to tune the system is probably not optimal.  Currently I have a pair of tubes in the balanced input sockets with the strong tube on the weak side and I am actually getting almost equal db readings with my sound level meter with both "input level" knobs turned completely up.  As long as I am getting that is there any need to adjust the trim pots? 

@billpete , a few posts or so ago I referred to an email I sent to a benefactor who had blessed me with a literal plethora of vintage pairs of 6sn7s. I really wanted to do something nice for someone who had turned me on to so many tubes either at bargain basement prices or flat out gratis, so I offered to give him a bunch of Mullard 12ax7s I had removed from an old Bogen receiver, and he replied,

"I appreciate the offer of the 12AX7’s, but I’ve laid-in a lifetime supply of my favorite 12AX7. For my ears and money, there’s no better 12AX7 out there today than the frame-grid JJ E83CC. That’s a really good tube."

I am not trying to convince you of anything, good or bad; I am probably among the least audiophile members on this board, but I just figured I’d offer you another perspective. It may be worth noting that he does not use 12ax7s in a preamp, but in a Prima Luna Prologue Eight CDP.

As far as 6SN7s go, knowing his high opinion of the JJ 12ax7, I once queried him about JJ 6sn7s and he told me that he had no experience with their octal tubes, but he had heard some people say that they were not bad and that for the price, why not check them out. Therefore I did put a quad in the phase buffer sockets, and to begin with I thought I did like them better than the EHs, but now I don’t know if there was much difference at all and maybe it was just wishful thinking on my part.

I will quickly share a story about some 6sn7s I bought on ebay. Among those vintage pairs of 6sn7s my friend turned me on to were a pair of RCA black glass VT231s. For several nights I had been trying out different pairs and I thought that some were pleasant sounding and that some were nice sounding . . . but the night I put those RCA VT231s in it was a serious "wow!" night. I found the detail to be mesmerizing . . . with more detail came better imaging and with better imaging the sound stage became more tangible. So going down the road a bit, I was drinking wine one night while I was surfing ebay, and I came upon some guy in France who was selling a sextet of those black glass RCA VT231s. I was like I cannot let these get away! I can’t remember whether I paid him five or six hundred, but where running six of those tubes didn’t sound bad, it wasn’t like six sounded incredibly better than two (I had been running the EHs for the other four at the time). And then, they started going cold on me one at a time. What I learned from that is that I will never buy used tubes on ebay again.

And good to read that we now have an answer as to what a "hybrid preamp" is. As an aside, the preamp I upgraded from with the SLP-05 was a "modded by Dennis Had himself"  SLP-90. The SLP-90 and SLP-94 both used tube rectification . . . the two rectifier tubes were on the main preamp chassis (as opposed to in the power supply box) on those two preamps. The SLP-05 uses only one rectifier tube (it is a different type, a 5AR4) and on the ’05 they put it inside the power supply box.

Anyway, @billpete , let us know your impressions with that slp-98. I have a feeling you are going to like it.

immatthewj

Again, thanks so much for all the info. I will absolutely post after getting the SLP98. I'm guessing that a bunch of new EH tubes and JJ tubes are not going to be all that pleasing to me but who knows? It will take a good while to burn them in as well. They only have 10 hours or so on them and likely have only been in place each time the unit has sold. I'm #3.