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When to change tubes

When to change tubes


Ok so your organ or guitar tube preamp or amplifier is sounding like a sick dog in the middle of the night and you want to fix it without spending a lot of money, huh?


Well changing the tubes can make a major difference and get your favorite amplifier or organ back to sounding like it should so you can impress all your friends with that great vintage tube sound.


So how do you know when to change the tubes and which ones to change? Here are some suggestions that have been helpful to others over the years


Symptoms that you may have a tube problem:


1.   Your amp/preamp is DEAD! – no sound at all and the tubes are not glowing. Check that your power cord is plugged in and your amp is turned on and the fuse is good. All tubes don’t go out at once unless they all have no power.

2.   You have sudden changes in output levels, loss of highs or perhaps mushy lows or muddy chords and some notes may sound weird, you have poor or no balance between notes or the amp makes “funny” noises like popping or crackling.

3.   Your power tubes (the big ones) may become microphonic and sound like a big echo or a torn speaker. This can also happen to preamp tubes like the 12AU7 or 12AX7 when they go bad, but usually the output gets low if the preamp tubes are deteriorating.

4.   The power output (sound level) isn’t as high as it used to be because you have to turn the volume up higher to get the same level of output. The cause is simple, output tubes deteriorate gradually over time along with a loss in both bass and treble responses.

5.   You have a tube that is not glowing or lit up but others are ok. This usually means one has prematurely burned out and the rest will shortly follow – better to get a whole new set and keep the old ones as backup (throw the bad ones away – recycle them as glass please!)

6.   Remember bad tubes can cause premature failure of other parts, such as the output transformer, speaker, and other vital components and these may already be bad if you didn’t change the tubes in time or regularly.


OK you have some of the symptom described, now what do you do?


Most musicians should change their tubes once a year if they play moderately loud and fairly often (like church organs or concerts). For Hammond organ players the power tubes in the tone cabinets often get very hot and lose power over time. You should also remember to check the tubes in the organ console as they are often the preamplifier which feeds the signal to the tone cabinet amplifier. Sometimes there is a separate reverb or vibrato amplifier or power amplifier (Like Hammond A-100, D-100, L-100, and M-100 series) in the tone cabinet (or console) and you will need to change these tubes also if you sense or hear a problem like I mentioned above.


In the old days, you could take out your tubes (mark which holes they came from) and take them down to the corner drugstore ands test them. Unfortunately tube testers are no longer conveniently available to do this and the test only lit up the tube and rarely tested it to the same conditions as in your amplifier with the correct voltage and bias conditions. So even if the tube was “OK” on the tester it still may be weak in your amplifier. So testing your own tubes is not a convenient option.


The most reliable alternative is tube- for-tube replacement and a before-and-after comparison. You can do this one tube at a time (like changing spark plugs one at a time) until your amp sounds better or just replace them all at once (easiest) and start to enjoy the great sound your amp put out when it was new to you.


When you do replace the tubes (and most people can do this), remember to turn off the amplifier (or organ console and tone cabinet), unplug the cord, let the tubes cool down if they were turned on and replace one tube at a time with the new tube (remove the old tube and put in the new tube and go to the next one, etc).


DON’T TAKE OUT ALL THE TUBES AND PUT THE NEW ONES IN WITHOUT MARKING THE HOLES THEY CAME FROM! Many tubes have the same pin configuration and will fit in several places they are not electrically compatible and may cause a major problem. But if you are careful this won’t be a problem and you amp will be happy with its new tubes and so will you!


Good luck and may all your notes bring happiness to their listeners!




Der Tube Meister


Check out my eBay store for tubes for many guitar amps and most Hammond consoles and tone cabinets from Hammond and Leslie and many Ham Radio/Linear amp tubes.