Just in case the image doesn't make it clear, we are talking vacuum valves (tubes if you are over there. Which is totally fine of course... No bias here. Phew!)
Ever since I first played a guitar, I knew the valve amp had prestige. Considering the vacuum valve was invented in 1904 by Sir John Ambrose Fleming, its impressive to think that such dated technology is still seen by many as the true sound of an electric guitar. In fact, in the early days, the guitar and amp were not considered individual to each other, but rather one complete instrument.
Now, with solid state doing a great job of matching that sound and profilers giving us a warehouse full of amp choices, I for one still love that warmth and dynamic sound that comes from my valves.
If only they didn't wear out! The times I've been playing at a gig and thought "are my valves sounding rough." Maybe they have just lost their edge or sound a bit flat. Or maybe that crash cymbal going off in my ear for the last 40 minutes has made me a bit deaf. (Use ear protection, folks)
So how do you know, and what needs to happen when its time?
Signs and Symptoms
Simply put, each valve is creating a new signal. As the current passes over the plates, it is influenced by the signal coming in. The quality of this new signal then influences the next, and so on. A 50w amp will probably have two output valves and at least three preamp valves. We spent good money to get the best sound we can and each valve is critical in that.
The most typical sign is unwanted noise. Hissing, popping and feedback are all potential indicators that it's time to change a valve. There might be other reasons, of course but actually valves make up for most of the problems in an amp. Hence they are considered consumable.
Like strings, valves loose some of their high end as they age. You might only notice when you change a set of strings, that they sound so much better, and hadn't realised how awful the old ones had become. The same for tubes (inclusive, see). Change them and all of a sudden you have crystal clear highs and are cutting through that mix.
Sometimes they go bang and take out a mains fuse. That's generally followed by panic and crisis talks about how to fettle the funds away for a replacement. I'm sorry to tell you that it is probably an easy fix.
What's Bias Got To Do With It
Well said, Tina. For starters, if we are talking pre-amp valves then absolutely nothing. Pre-amps are the little ones. The ECC83 is a typical example. They are taken care of by the surrounding circuit and are plug and play. Often, a set of new pre-amp valves will make all the difference and wont leave you out of pocket at all.
Power or output valves is where it gets more technical. Taller than Pre-amp, they need a regulating voltage to prevent a riff in the space/time continuum (also known as voltage spikes). This is where the bias comes in. Different valves have different bias voltage requirements and different amps have different ways of adjusting them. Marshall will often place the test point and adjustment outside of the main chassis - very helpful. Blackstar and Orange can be a little more cryptic and generally involve removing the chassis and inspecting the circuit board. Mesa Boogie don't like us messing with their stuff so provide no means of adjustment and instead sell us expensive, factory tested valves.
All of the information is available on the internet and with an hour or so searching and a few simple tools, you can fit a new set of valves and bias, where necessary. That said, you are risking death. The capacitors inside an amp hold very high voltages. Higher than mains voltage and can kill you. If you are not sure of what you are doing, ask someone else. It really won't cost much more to get a professional to do it and is certainly cheaper than a funeral.
Do It, Do It Now!
Alright Arnie. Settle. There are a few amp techs in Essex and Suffolk and any will be very happy to swap a set of valves for you. I have often heard once a year recommended, but to be fair the variables are too wide for that prediction. Most valve manufacturers will give you three months guarantee on the valves. On the other hand, I've run the same set for years with no problem.
If you are unsure, or have decided you want a change, Hale Guitar Studio are very happy to help. We have repaired a number of amps with faults including blown valves, dirty pots and planet consuming capacitor shorts. We've got your back, Jack.
Happy Riffing
Chris
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