:rockon: thanks a lot Wild Bill. You are a very helpful fellow.
Do you recommend getting my power tubes replaced any time soon?
I have used the amp maybe 20 times on stage with the volume pretty high (3 or so o'clock) but not more than that (too heavy to carry around)...and the rest of the time, I play the amp at home about 4 times a week, perhaps 2 hours each time, at low volumes.
Whenever you replace power tubes you should always have the bias checked and set. This ensures that the amp is always running in the "sweet spot" and that the tubes will have the best life. If you don't do this it will be a total crap shoot as to how the bias setting is affecting your output tubes (the big ones). If it's setting the idle current too low the power will drop and the sound will get glassy and thin. Too high and the tubes will burn out sooner.
How long should they last? If everything was set correctly a good set of tubes in an amp that gets played a couple of gigs a week should last a couple of years or more, in my opinion. The preamp tubes (smaller ones, usually marked 12AX7) do not wear out like power tubes. They handle voltage, not big gobs of current like 6L6's and EL34's. They can develop faults and need replacement but other than that they can last for years. I've pulled tubes over 50 years old from old amps that still work just fine. In your case with such light duty I would't be surprised at 4-5 years, or more for the output tubes!
As for the preamp tubes, run 'em till they die!:smile:
How do you know when they're getting weak? Well, that can be tricky. Usually the power drops off and the tone can get muffled. I tell my customers that after a year or two if they're worried about it they should bring the amp back to me. I can put the tubes in my tube tester and also re-check the bias to see if it has drifted. This is a fairly quick thing that takes about an hour and my shop rate is $50/hr. I also get a chance within that time to get a look inside the amp for a quick inspection. If I have to replace any tubes I can do that within the hour and so the only extra cost is the tubes you'd have to buy anyway.
Some amps bring the bias test points and adjustments to the back or top of the chassis so you don't have to open up the amp when changing the power tubes. Me, I pull the amp out of its case anyway even though I don't have to. I like to check inside! The amp is on my bench anyway and the customer is paying for a full hour so why not do the inspection? If your car is on the hoist for an oil change they're gonna take a quick look to make sure your transmission isn't falling out or something!:smile: Same with an amp.
You had asked about pulling tubes for less power. It's often done but you have to worry about a few things.
First off, only the power tubes are involved. That's the big ones that I told you work in pairs or combos of pairs. A 50 watt amp will have two output tubes and you can't pull one without unbalancing things and asking for trouble. A 100 watt amp will usually run 4 tubes, as a pair on each side of the circuit.
You can pull one pair. That would be the two outer or the two inner tubes, NOT two from one side! That will drop the power in half. You will have changed the load on the tubes through the output transformer.This means that if you had an 8 ohm speaker cab you should set the amp to the 4 ohm setting. If the cab is 16 ohms then set the amp to 8.
This last bit is not super critical. With tube amps if the speaker setting is not right the tubes are usually tough enough not to care. The tone might change slightly (maybe better!) and you might lose a week or two of tube life but that's about it.
Hope this is useful!
:food-smiley-004:
