A local tech told me that as long as I replace my power tubes with tubes of the same type (6L6 for 6L6, EL34 for EL34), that there is no need to rebias. Is that correct?

I ask because a rep at tube depot told me something different. Here is what the tube depot rep said:

"If your amp is variable bias (also called fixed bias), then you should always have your amplifier re-biased. The only time when this is not the case is when you have previously purchased power tubes from TubeDepot.com. We rate our tubes using the Bias Point system. This is a "Real World" measurement of the tube's performance. When you receive the first set of power tubes from TubeDepot.com you will have to re-bias your amp. Once you have biased the amp you will never have to bias that amp again as long as you purchase your tubes from TubeDepot.com. When re-ordering power tubes for your amp, just ask for the Bias Point that you received before and that is what you will get. Now you have plug and play power tubes. This is true with any power tube in the family of tubes you are buying for your amplifier. Example: If you have Sovtek 6L6WXT+ then any 6L6 with the same Bias Point will work perfectly."

Well, I talked to another tech and he confirmed that the rebiasing is needed, even if the tubes are the same type.

You have to rebias if they are the same type El34 6L6 etc Some companies have a number on the tube and if you get a replacement set with the same number you supposedly don't have to rebias (Mesa Boogie does this). It is always good practice to have it checked anyway.

I took my amp in to be rebiased and the tech told me it is the type of amp that has a resistor that sets the bias and is selected by the manufacturer to give a fairly low bias so that the tubes can just be changed out and still be OK. So he decided not to rebias it.

the same tubes (i.e. replacing from el34 to el34) doesn't mean you get the same brand, but even that their parameters are slighlty different.
it should be ok (i mean you will not damage an amp), but it may sound deifferent and you should re-bias the amp.
even amps with fixed bias can be re-biased, which usually means replacing one resistior (sometime one resistor per tube).
i hope it helps

quote:

I took my amp in to be rebiased and the tech told me it is the type of amp that has a resistor that sets the bias and is selected by the manufacturer to give a fairly low bias so that the tubes can just be changed out and still be OK. So he decided not to rebias it.

Yep. I have an amp with a resistor that sets the bias as well. You don't NEED to rebias but it certainly can be biased if you want it to be.