Audio Research Ref 3. 6L6GC or 6550C

The 6L6 is probably close to the KT66 than the 6550. The 6550 was derived from the earlier 6L6 and has higher output and plate voltage than the 6L6. As Mistycat advised, check with Audio Research because the earlier models might have had different circuitry values which could might not properly handle the 6550.

Thanks for your answers. Mistycat, you know if the sound with the 6550C is much better?

Hello Fcano , after one year of use the REF 3 , I received from the ARC dealer a new tube , the 6550C , to replace the 6L6 , there were problems with this tube , due to the specs.The new tube had higher specs , and the sound is much better.No circuitry changes had to be made , I could replace it by my self.So please use the 6550C tube.Or buy a NOS Tung sol 6550 , see other thread on this splendid forum.This kind of tube I use now about half a year .Does sound again better than the Russian Sovtek .
Greetings Hans

Hello Hansk46 . Your answer has interested me a lot. Unfortunately I do not speak English and the translation carries out it the google translator. You mean me that can change the 6L6GC by the 6550C without make no change?. I expect its answer and thanks.

Francisco Cano