CAD SLI-80 Signature: Re-tubing

Decided to re-tube my demo SLI-80, as it makes me a bit nervous to not have an accurate idea as to how many hours are on the power tubes.

I definitely won't miss the cheap Sovtek 6550's that came with the amp. I very much prefer the sound of the Svetlana/Winged C 6550 variant. I am looking for feedback from SLI-80 owners that may have tried using EL34's or KT88's, and which tube they prefer. How does the sound and/or power output differ from one tube to the next?


I am now using EH KT88's in the triode mode and they are a great sounding tube. I tried EH EL34's both triode and ultralinear bisased at 50 for ultralinear and 70 mA for triode. and the bottom end was very tubey and the highs not as bright as compared to the KT88's. I wouldn't recommend them for the SLI80.

For a rectifier I'm using a nos National Union 5U4G from the 40's which I like a lot. Tube Depot has them. Sylvania chrome dome 6SN7GT's from the 50's and a pair of Amperex 6DJ8's orange globe logo A frame getter from the 60's round out the tubes.


I am using EH KT-88's in my SLI-80 F1. And they sound a lot better than the Sovtek 6550's.....not just by a little....I mean a whole lot better.
I also agree with Larry on the Sylvania 6sn7gt chrome domes.
I just ordered some NOS tubes from Andy at Vintage Tube Services today:

Sylvania 6SN7-GTB
Mullard 6922 (the real thing, not the 70's and later stuff everyone else passes off as NOS)

I'll work those in, one matched pair at a time. Unfortunately, I've blown my NOS budget for the time being. I'll have to go with current production power tubes, as the NOS tubes are pricy. Thus far, it seems like the KT-88 is a favorite.
I have had the 1950's RCA 5U4G's in for about a week now...very cost effective improvement. The amp is a bit more dynamic, with improved low-level detail. The soundstage is a tad wider, and much more coherent.

The 1950's Sylvania 6SN7's go in next. The Mullard 6DJ8 tubes didn't test out well enough, so I got a pair of Bugle Boys from Andy instead.
I use Sylvania 5U4G rectifiers (and RCA 5U4G which are a bit darker), TungSol three-hole grey plates 6550, Sylvania VT-231 (and sometimes KenRads JAN CKR 6SN7GT which are very colored but good and GE 6SNTGTA and GTB) and Siemens 6922/Amperex 6922 orange globe).

I also tried the Mullard EL34 xf2 and xf3 but was not very much satisfied but I found that the RFT EL34 are rather good with this amp. YMMV of course.
My quick take on the addition of the Sylv 6SN7GTB'S and Bugle Boys...greater inner detail, and a more natural/organic tonality. The soundstage width, height and depth are improved border on holographic.

The SLI-80 is a very fine amplifier, but the addition of the 1950-60's tubes takes it to a whole new level (cliche' alert!). This was my first time buying tubes from Vintage Tube Services, and I can't recommend VTS enough...Andy knows his tubes. ;)