FAQ #16g. But it sounds different when you first turn it back on. What is the warm-up time for this gear?
We generally recommend 45 minutes warm-up time for everything to reach operating temperatures and sound like
it’s supposed to. It will reach “listenable” temperature, however, in just a few minutes.
FAQ #16h. What about break-in time for new gear? We burn in the gear for a couple of days before it is shipped
out. Folks report that after about a week of break-in that it sounds better. Some of the more fussy people of course
report that full break-in takes much longer....
FAQ #16i. How do I know a tube is broken? All the vacuum has leaked out.
FAQ #16i.i After the vacuum leaks out, where does it go? Is there some way to collect it and put it in another
tube, to make it last longer? You have to suck really hard.
FAQ #16j. No really, how do I know a tube is broken? Usually a tube whose glass has been broken or cracked
usually will have a white powdery like substance inside it where all that silvery stuff used to be. No, it is not co-
caine and we didn’t put it there..
FAQ #16k. Does the glass explode? I haven’t seen it happen. Usually the glass will just crack at the base of the
tube if it is going to physically break due to a sudden change in temperature and “all the vacuum will leak out”.
FAQ #16l. Other than outright failure of a tube, how do I know when it is time to re-tube? Generally speak-
ing, for the small tubes, if you notice an unacceptable increase in background noise (“hiss”) then the tube who is re-
sponsible for making the gain in the circuit probably needs to be replaced. The tube(s) making the gain will usually
be shorter than the output tube. Common types we use for gain in most of our circuits will be 12AT7, 6201, 12AU7,
5814, 12AX7, 5751, or 6072. The output buffer tube in most of our line-level circuits will be either the 7044, 6414,
or 12BH7. These tubes usually don’t cause too much trouble and either work or don’t work. Turn the lights off and
see if you see the little tubes glowing. Look for one that looks like it has cocaine in it.
For the power tubes in our amplifiers, after a few years if you notice a small revolt going on where several of the
output tubes are misbehaving or getting hard to bias, you might consider doing a full re-tube. Keep the old ones that
did not join the revolution as emergency spares.
FAQ #16m. Can I change a tube myself? R.T.F.M....do you call in specialists to change your light bulbs for you?
See page 5 for details on how to accomplish this task.
ALL YOU NEED TO KNOW ABOUT BIAS...
What do I need to know about BIAS? Bias is a simple DC (negative) voltage that sets, what is called, the “oper-
ating point” of the tube. For our purposes it “fine tunes” the current going through the tube. We want each of the 4
tubes per channel to be equally sharing the load. This gives the amplifier’s lowest distortion and the tube’s optimum
life. When we set “bias” we are adjusting that voltage and measuring the current at a pin called the cathode. The
cathode is connected with a 10 ohm 3 watt resistor that allows the more convenient voltage measurements from ter-
minals right on the top panel. These 10 ohm resistors also have a second job. They are fuses in case of a really nasty
tube failure. Sometimes a tube will die in a way that burns up this resistor (with a little puff of smoke) and then with
a new tube you will only measure zero at the terminal for that tube. The resistor should be replaced by a technician,
but it should only take ten minutes. Can you solder?
How often should I check these BIAS points? Some people never do. It really should be done when you change
a tube and it is very likely that a little adjustment will be needed. We suggest that you check every 3 months - that
way you are assured that the amp is running optimally and will spot a tube on its way out. Some check every
month, once a week is getting a little obsessive.
What tools do I need? Just two. A small flat screwdriver (insulated handle) to adjust the trimmers. You also need a
voltmeter or multi-meter, one of which we’ve provided with your new Stingray II. How convenient! Any multim-
eter will do; it doesn’t have to be a good one. RadioShack sells them as well, if you want to purchase a different one
for some reason. As long as it measures DC volts between 0.1 (100mV) and 1 volt, you’ll be just fine.
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Summary of Contents for Stingray II
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