Eurotubes IMO is the best of the 3. They really push the JJ's but theres nothing wrong with that. They also have a special tube "cocktail" for the SV mk1 (with SVpre of course) I am running all JJ's in my mk1. I've had several different brands and I've settled on JJ's. The people at Eurotubes are very cool and eager to help. Not to mention the fact that every time I have called them a real live person answers the phone not a machine!

I like the 803 in V1, but I've got V1 modded for gain (hotter than my modded SVPre in fact).  In a stock amp with the SVPre installed the SVPre is the hottest gain setup so the 803 should shine there the most.  It has a very nice high gain tone IMO.

A stock setup V1 slot is not getting any gain so an 83s should do good there.  An 803 in a stock setup V1 would be a waste of talent.    V2 is the PI.  There you want a quiet tube.  A balanced tube is fine but most importantly is a quiet tube.  Your very best 83s is good there.  Its going to coast anyway but any noise there is going to really show up in the power tubes big time.  Not a good thing.

I love a good 803s really stressed out running high gain.  It seems to like it there too, but it might not last real long.  Mine only lasted about a year but I was stressing it out all I could - all the time.  You can stress an 83s too but it will get muddy and loose quicker than an 803.  An 803 can take more and still sound strong IMO.  I like them in the gain slot cranked up.  Even not cranked they beat an 83s IMO, if you can get a quiet one.  With gain there is noise so little noisy 803 is ok but noise in low gain is not cool.

Good luck man

Later

M^T

I can't wait. 

I don't think there is any way the cap mod could make the power tubes sound muddy, so you can probably rule that out.  lol.  IMO the original little square looking caps that came in my SV were very restrictive to the signal, not to mention that I can't imagine they were allowing the full signal through them without crimping something out - somewhere.  I can't imagine any amp builder in the world that would choose those original square caps to put into any kind of guitar amp - can you?   So based on that idea I can't see how they are a benefit by being in there.  The SOZO's on the other hand are being used by quality - experienced custom amp builders all around the world and are also considered by most to be indeed top quality, so they must be better.  The one way to find out is to put them on a scope and see first hand what freqs are passing and which are being blocked/restricted.  The amount of blocking/restricting is what is being heard when one tried the SOZO cap mod.  It does open up the amp and opens up the tone, but thats about all it does.  Nothing should happen to the power tubes except they might get a fuller more quality signal to amplify, which IMO should be easier overall.  If those stock caps "leaks" as much DC as I imagine then the SOZO mod would actually help the power tubes to function better without being injected with a bunch of DC component.

When a tube amplifies the signal it comes out of the tube into the high voltage DC current on the plates.  In a 12ax7 that is pins 1 and 6.  There we attach what is called a coupling cap (our SOZO mod).  This junction is similar to a "Y" connection.  The high voltage DC current, about 120 volts in a stock 112, is on one side of the "Y" and the coupling cap is on the other side, with the tube's plates at the bottom of the "Y".  The signal comes into the tube at pins 2 and 7 (the grids).  The amplification inside the tube makes the high voltage DC current on the plates fluctuate.  This fluctuation is then within the DC voltage.  The coupling cap only allows the AC component (the fluctuations in this case) to pass through while blocking the DC current.  A better cap allows a wider AC component through while effectively blocking all the DC electricity out.  The results of this is that the signal (the AC part) passes though the cap to the next gain stage inside the amp.  If a coupling cap allows any of the DC electricity through it then the next gain stage will show signs of damage/noise/etc/etc, which is not good in any way.  A poor quality cap cripples the AC by being restrictive to all/part/some/etc of the signal which in turn modifies it into sounding like something else.  Amp voicing is done by changing caps which in turn is somewhat changes the tone of the signal or spectrum of the signal which is allowed to pass through.  If you install the SOZO mod and find that the amp now sounds differently then that difference is only the actual difference in the quality/throughput/spectrum/etc of that cap, not to mention any DC component which might now be blocked.  A poor quality cap might only allow one part of the signal (freqs) to pass unrestrictive while restricting all the other parts of the signal to some varying degree, for the most part uncontrollable and somewhat unpredictable.  Putting a cap on a scope with a sweeping frequency would show its ability/quality/etc.  A high quality cap should pass the original signal unmodified to the next gain stage, within its designed range and capacity, everytime,  but I don't think there is such a thing as a perfect cap.  I have no doubt my SOZO's are much better than those little square shrimp size crapo caps that came in my SV ever could be.  IMO the SOZOs should make my power tubes sound better, fuller,  and last much longer then before, not sound worse, muddy,  and burn out sooner.  There hast to be something else wrong here.  lol

Hope this helps.

Good luck

M^T