I bought these monoblocks many years ago from a Little Rock Central High School teacher. I sent them to hot glass audio for a rebuild. Anyone who remembers that con knows it was a miracle I even got them back. He broke all NOS tubes in shipping. I sold them to my brother because I was frustrated but he just sold them back to me. The nightmare continues. I completely gutted them and rebuilt them from scratch but I did have professional help. I added bias adjustments removed a 12AT7 preamp section and upgraded power supply with a beefier choke and caps. The power tubes switched from, 6550 to KT90's which are from the collection I inherited from Daddy Dee. Thanks again to Daddy Dee. The tube compliment is 2 x KT90, 2 X 5AR4, 2 x OD3, and 2 X 6SN7. They sound really good when turned up but still a little transformer hum to work out. I need to tighten them down. Not sure I need freaking 90 watt amps.