If your amp features auto-bias you don't need to do anything but replace the tubes. Some manufacturers say the tubes don't have to be matched. That may or may not be true but I suggest buying matched tubes anyway.
7 responses Add your response
If amplifier is truly auto-biasing, you don't need to use matched tubes. The amplifier circuitry will match them for you. Best to do this before you turn the amp on after it is cold.
Also, I don't know what tube rolling means to you, but you need to use the same output tubes or an approved equivalent. You can't just plug in anything that has the same pin pattern.
That depends on the circuit. What amp is it? It helps to know that, so maybe guys who have your amp will read this thread and put your mind at ease...
If it is a true auto bias circuit that adjusts each tube individually it wouldn't even matter if your power tubes were matched. Look at the BAT VK-75 or the Primaluna amps... those have auto bias circuits and do not need matched tubes. If it's just a simple cathode bias you'd want them matched, but you could still just pop them in yourself.
The only company I can recall that recommends sending an amp in for re-tube is Audio Research... but none of their amps are auto bias.
The 6SN7 tubes in your amplifier are in self bias.
So, you can tube rolling 6SN7 tubes in your 6SN7 drive 845 amplifier.
845 tube rolling may require to rebias 845 and re-set hum pot--it is the standard procedule for most 845 amplifiers. Many users are not capable to do the 845 tube re-bias(high voltage and high current involved).
I would recommend you do not touch 845 for tube rolling. Plus there is no better sounding 845 from vintage time unless you pay $2000 for one pair of used RCA 845.