Tubes (Valves) 

The more you know, the healthier you will be 

HOW LONG WILL MY TUBES LAST?

The usable life of any tube will depend on how hard it’s actually used in the circuit. Some circuits will use tubes harder than others and we all know that some players play harder than others. Power tubes can last years in a light-playing situation while lasting only 6 months in heavy playing conditions. It is also dependent on how loud you play and for how long. Also if you don’t correctly match up the impedances, this will put strain on the power tubes and wear them down much faster. Some people keep the amp on all day wide open and this greatly reduces the life. The bad news is that tubes have no definite life span much like light bulbs. We have spoken to a guy who went through five sets of NOS Groove Tubes in 6 months! Now that's a lot of money, especially seeing as he is using a 6100 (four 5881 power tubes plus seven preamp tubes).

Pre amp tubes will generally last much longer than power tubes. Basically the pre amp tubes will last twice as long as the power tubes but again; there is no definite life span so no one can be 100% sure.  

WHAT THE HECK IS A RECTIFIER TUBE????

All of our Marshall and VOX tube amps require DC (direct current) to work. However, as you know, the power we get from the wall is AC (alternating current). So, a device known as a rectifier is utilized within the power supply of an amp and its job is solely to convert AC into DC - hence the name "rectifier." In most modern tube amps a solid-state device known as a diode does this “rectification”. However, a few "older" amps use a tube as their rectifying device and we happen to distribute four (4) of 'em! They are the Vox AC30 (GZ34 rectifier tube) AC15 ( 5Y3 rectifier tube), the re-issue JTM45 (GZ34) and the 1962 Bluesbreaker combo (also aGZ34).

Now, as the guitar's signal never actually passes through this part of the amp's circuit, one would think that a rectifier tube has no direct effect on the sound of the amplifier… well, that's the theory anyway! The truth however is different. The thing is, the rectifier tube has a direct bearing on the power supply tube for the other tubes and, due to its relative inefficiency (compared to a solid-state rectifier), it can and will “sag” when the demand for power is higher than it can handle. And, as it happens, a lot of players like the sound and feel that results from this "inefficiency." To hear and feel this "sag" in action, plug into a JTM45 or a 1962, crank the thing up and then start attacking those strings! Believe me, once you've experienced this "sag" in action, you'll fully understand why it is so named. I hope this information helps. Be careful out there, wherever you are…

WHY DO I NEED TO CHANGE MY TUBES?

There are two main reasons why amplifier tubes need to be changed. The first reason is that the tube(s) simply burn out, causing a malfunction with the amplifier. On the JCM900 series amplifiers there is the fail safe fuse which is built in to indicate power tube failure. The tubes need to be changed immediately so damage to the transformer is avoided. As I stated in my previous tip, tubes have no definite life span and can burn out at any time. Thus the 90 day warranty on them!

The second reason and perhaps the more important is to improve the performance (tone) of your amp. The effect the tubes have on your amp is much like the effect that strings have on your guitar. The more often you play and the more aggressive you play, the faster the tubes/strings will wear out. Playing loud and hard will cause your tubes to lose power and tone long before they finally die. This wear down process is very gradual and most people (including myself) wouldn’t recognize the difference in tone until new tubes were put in and biased by an authorized technician. I always mention to customers that if a power tube goes that they should replace all of them so they will have equal wear over time. This will help provide a more even tone and back up tubes are always a good thing.

A common problem that we’ve all seen with tubes is a microphonic pre amp tube. This is the culprit that causes that high end squealing even without a guitar plugged in. I think Ted does that also….. A way to check this is to unplug the amplifier, remove the back panel, turn the amp back on and then let the tubes warm up. Take a pencil and gently tap each pre amp tube to see which one has a loud ringing or crackling sound. They will all ring to a certain degree but the “bad” one will be much more noticeable. Replace this one immediately. A second way to find it is to pull out the suspect one(s) and replace it with new ones. This is simple because as you know there is no bias procedure for pre amps tubes and any non ­idiot (read: non-keyboard player) can do this without hurting themselves, the amplifier or others. Plus it’s always a good idea to have replacements for gigs anyway.

HOW DO I KNOW THAT MY TUBES ARE WEARING OUT?

These are the most common signs that tubes need replacement.

1)      Excessive noise (hiss, hum) including squealing or microphonic tubes

2)      Loss of high end. Little or no treble.

3)      A muddy bottom end. Sounds like there is too much bass and note clarity is lost.

4)      Erratic changes in the overall volume. Can go up and down but generally it goes much lower.

5)      A blown H.T. fuse.

6)      The freaking amp doesn’t work!