Do preamp tubes need to be biased?
With preamp tubes, you don’t need to worry about things like biasing or using matched pairs as you do with power tubes. As long as your new tube is the same model as what you’re replacing (12AX7, 12AT7, 6SN7, etc.), you’re good.
Can I mix and match preamp tubes?
You should be able to swap preamp tubes of the same type without problem. For example, any 12AX7 should be compatible with another 12AX7. With power tubes, you can swap different brands of the same tube. (For example, 6L6 tubes from different manufacturers.)
What happens if tubes are not biased?
If you changed to tubes with a lower resistance without biasing the amp you would quickly burn through those tubes and potentially damage the amp and yourself in the process. This is because the amp is still pushing out current at a higher level than the valves are able to take. Until it’s been correctly re-biased.
Do 12au7 tubes need to be matched?
Not all 12AX7 preamp tubes are identical in their makeup though. Manufacturing processes vary, as do the quality of the materials used to construct the tube. Logically, one would conclude that using two of the same make of 12AX7 preamp tubes is a good idea.
How often should you Retube an amp?
They will usually lkast up to 10 years without a problem. However, if they get microphonic, which is not uncommon, or noisy, then change them. There are no specific rules. It is like your car, you should get it service regularly if you want it to perfom well.
How do you know if your tubes are matched?
To be specific, mis-matched tubes can be bias-adjusted so that output sound is centered. However, if the tubes aren’t a true match, then one channel will not sound as “lively” as the other – sort of like a dead can. With experience, this is easily discernable by ear.
Can you change tubes without biasing?
Sure, you could stick some tubes in there and they could be dead on, but that ain’t gonna happen. If the bias is too hot, you will probably ruin the tubes before you get the amp turned off. To cold and it will sound like crap. It’s useless to take a chance with the bias.