Speakers connected - check. Multimeter connected - check. 0.65 VDC - check. The four 6H30's can go into any of their respective sockets. After this setup play some music for 30 minutes. Keep the meter connected. Then check the meter reading and re-adjust to 0.65 VDC. Play some more music again for 30 minutes. Check meter and re-adjust if necessary. Then, for the third time, play some music for 60 minutes, check meter and re-adjust if necessary. I recommend checking the bias again after 24 hours use. Then after seven days to see if it has remained stable.
Re-tubing my Audio Research Ref 110
After taking advice here I've ordered 8 matched KT120 valves and 4 6H30 (getting difficult to get as can't import from Russia now!)
I've read the ARC instructions but want to make sure I've understood correctly - don't want to blow it (or me) up.
I turn it on for 15-20 with the speakers connected but no signal going through (so disconnect the source or mute?)
The I attach the multimeter, one to the yellow and one to the black beside each pair of tubes/valves. Does it matter which wire goes to which?
Then I turn the blue screw (guess the one adjacent to each set of the two tubes is the one?) The manual says I need to adjust to get 0.65V DC on the meter but that's for the original spec 6550 tubes. Is it the same for KT120 tubes?
And do I just stick the other 4 x 6H30 tubes in - do they need anything?
- ...
- 9 posts total
Do the KT120 just drop in as a direct replacement for 6550c? Did you contact ARC to confirm this and to find out what the KT120 should be biased to? Other than that, @jasonbourne52 provided the steps. Just have you source(s) powered off when biasing to be on the safe side. |
No need to call ARC. Yes, you can substitute the 120's for the 6550's*. And yes, as Audphile1 said, you want to disconnect the source (music should not be playing) when setting bias. You don't need to take all those steps the first guy who responded specified. To prevent any wildly off bias, wait ten minutes with the amp on and speakers connected but with no music playing and then do the first bias setting. And yes, your amp comes with one pot adjusting one tube with another "slaved" to that tube. So one bias pot for two tubes. The bias pot sets one tube to a specific setting and then the slaved tube is merely expected to be within a specified range. Don't sweat it. After that initial setting done to prevent any "flare ups" of potentially badly out of whack bias, just play music for an hour or two and kick back and THEN stop the source and check bias again resetting as necessary That is all you need. Not all that other stuff. After 20 hours or so you can check again. If your tubes won't bias to spec, you need to rotate the slaved pairs up to three times with different combinations and if they still won't bias to spec you got an unacceptably matched set (mismatched set). * KT120's are polarizing. They have grunt and extension but in the opinion of many lack the soul and midrange presence of good 6550's/KT88's. But you have already bought the KT120's so enjoy them. They are a good tube. Nothing to lose sleep over. |
- 9 posts total