imhififan979 posts03-25-2020 8:03pm
"Can someone help me understand what the specific function each type of tube performs in a power amp?"
This has yet to be answered...
Input stage: 2x 12AX7
Rectifier: 1x 12AU7
Drivers: 2x 6SN7
Power stage: 4x KT120
I read above the power tubes have some issues also. Nothing I've ever owned used KT120, or 150. I have always been a 6L6 (lower wattage) 6550, KT88 and 90 user, when it comes to power tubes. I'll bet if they were bios different, the problem might go away. AUTO bios can be an issue..for some valves.
6SN7s have been around a long time, there has to be some great valves out there for that one too. Very good valve. Use to call um double trips,
actually two valves in one.. Can't tell me matching this valve isn't important.
The 12AX and AU7 will cost the least. TONs of options. MATCH the tubes. If there is no way to bios the signal tubes, matching makes a big difference. The quality of the valve, prone to vibration (BIG ISSUE).
(Valve tap with a thin wooden dowel), if you don't have a tester. An old
school, valve amp guy, showed me that one, the tap test. (Lightly), not a snare drum. Hold the top, one finger, tap the side.
I've also gotten serious changes with HOW the unit was and is bios,
there is a range say 200-300 (just a number). It can change how the amp sounds A LOT.. The 20-50.00 usd on signal tubes, bios options (if there is any), matching, unit vibrational control (good idea) TWEAKS in the valve world for sure, and dirt cheap..
These, along with, placement, treatment (heaver drapes), controlling the bass usually cleans up EVERYTHING. just a bunch of stuff you could do for just a few bucks, in the name of MIDS...You'll get it..
Respectfully The OldHvyMec..