NOS KT 88s or GE 6550s

Contact Ed at C/J and find out if you can put KT-120's in that amp.

Well, it make take a few years before damage happens. This of course depends how over built the heater winding of the transformer is. Obviously 4 KT-120's would be less of a burden than 8 etc.

I don't know what all the fascination is about with the GE 6550's. I always remember them to be just okay and had issues with them in Dynaco Mklll's so i never used them. Later versions of the tube had major issues with high plate voltages or high bias currents hence the Dynaco issues. For that matter so did the Genelex KT-88 as they would routinely arc and blow the fuse. I much preferred the Philips Sylvania 6550 that Audio Research used for many years. An excellent tube and much more robust than the GE IMO. The Sylvania was a smaller tube than the GE.

I have heard them in an Audio Research D-76A as well as a D-79. They sound great but the newer versions of that tube are just not very reliable.

For a few years Richardson was making 6550's using GE's tube machines that they had purchased. Tube looked the same but that's where the comparison ended. They were miserable.

They were not branded GE. They looked identical but they obviously got the recipe wrong. I think they scrapped the idea. I think the reason no one is making tubes in the U.S. is more about osha and the nasty chemicals that are used in the process of making a tube than anything else.