This is the tube that GT "traces curves" on sophisticated equipment and packages with their Special Application Group (SAG) kits. STRONG GAIN with this tube--pushing a STOUT signal through the front end of a cascading gain amp is what this tube does GREAT. Additionally, the cleans sound like someone took the "blanket" off the amp--mids are definitely THERE!!! My tech also installed a Matched Phase Inverter (MPI). These tubes made a B-I-G difference in my FENDER:-)

I've tried several other 12AX7/ECC83 type tubes and keep coming back to the Groove Tubes ECC83-S. In fact, I like it so much, I replaced ALL my preamp tubes with it! It has a good hot tone, but still clean enough for when you don't want to play loud. It woke up my dead-sounding 5150 amp.

I replaced the crappy stock Sovtek tubes that came with my Silkyn Super 50 with six of these. What a huge difference. Dan Torres recommended these, and as always,he was right on the money. My amp sounds like a combination of a Marshall, Orange, and a Vox. It's sick! I also put a Eminence Wizard speaker in it too. They're a perfect combination. I highly recommend these tubes!

Recently purchased a barely used Marshall AVT 50 and decided to purchase this Groove Tube as I was looking for a lttle better tone and sustain. WOW! What a difference. More tone, more sustain, a much better sound and even more power, which I really didn't need. I am now totally satisfied with the way this amp sounds and this tube made a difference for me.

I put one of these in my Marshall AVT50h and it sounds like a brand new amp. I would recommend buying these if you have a hybrid amp or just need new life in your tube amp.