Introduction
If you have recently bought a new valve amp and you have never had a valve amp before, then this short blog will give you a quick understanding of the valves in your new ( or, new to you) amp. I receive a lot of messages and emails on folks who are new to valve amps. I thought I collate the common things in this one blog. I have tried to keep all the techy stuff out and just mention some of the key points. I have kept this at high non techy level.
Benefits and limitions of valve amps
Valve amps sound so much niicer than the average solid state amp . They are generally warmer sounding. A 10 watt valve amp usually sounds louder than a solid state amp. If you bouht a new amp, did you check the warranty on the amp. Probaby says 2- years. However, the small print usually says the warranty on the valves are something like 90 or even 60 days.
Valves were invented over 100 years ago. The popular 6L6 output valve came on the market around 1937 and has been in continuous production for 87 years. Transistors appeared around 75 tears ago. If you think of cars from 1937 versus today, this puts into perspective just how old this technology is. Valves are made of glass and they are mechanical devices. This makes them much more fragile than a semiconductor chip. Drop a transistor and a valve onto concrete from a second floor window and there are no prizes for guessing which one will still work. Valves consume a lot more power as they have a heater inside to get them up to temperature. They work at HIGH voltages.
Wear on valves.
Unfortunately, valves are like filament light bulbs. They wear out and need replaced. There are mechanical and electrical aspects involved in the wear and tear.
Valves loose emission (like a car engine looses power as the mileage increases) over time and they become dull sounding. Think of this as “electronic wear”.
Valves are constructed using metal plates inside. The plates can work loose over time due to the vibration from the speakers , especially in combo amps. Loose plates cause the valve to become a lot more microphonic. It acts as a microphone and this can cause unpleasant ringing or cause acoustic feedback just like a microphone.
All valves are inherently microphonic but when new this is minimal. It gets worse with time.
Valves will tend to go microphonic if your amp is in and out of vans and being moved about, In extreme cases a valve can have get a bad knock when being transported and this can crack the glass. It is a vacuum and when the glass is cracked it lets air in and the valve goes white inside. The featured picture shows a normal valve and one on the right with a gas leak. due to the top being broken. It is dead and needs replaced.
It is not simple to answer how long they will last. Key factors are how loud the amp is played ( more wear on the output valves), how often the amp is transported . How many bumps and shocks the amp receives. Higher volumes run the output valves harder and this also influences their lifespan.
Not happy with the sound?
As valves age, they become dull sounding. The amp looses all its high frequencies. You are turning up the treble and presence controls to try and compensate. You eventually get to 10 on the controls.
Output valves can start to make a random wispy sound or random crackles when thay aee old. This is an early warning to think about changing them.
How long will they last?
You have hopefully seen from what I have said previously, there are a lot variables. An amp used occasionally at low volume will not need valves changing for much longer than a gigging amp that is on the road and being played loud. The exception is if you are using a power soak to lower the volume. A typical power soak runs the output valves at higher power and this shortens their life.
A very rough guide on lifetime is :
- 1800-2000 hours for output valves.
- 2000-3000 hours for the small preamp valves, rectifier valves ( GZ34 etc)
This includes standby time.
How to do simple diagnosis without test gear
This is not.a 100% way to find a faulty valve but it can give you a reasonable guide in narrowing down a problem. Here are the steps :
- Take a good look and see that none of the valves have gone white inside. Make sure the metal plates on the output valves are not glowing red hot. This is a sign the bias circuit is either set wrongly or the bias circuit itself is faulty. Have the amp checked by a tech if this is the case. You do not want to replace the outputput valves and then wreck the new ones !
- Look and see if the heaters are all working in each valve. The small preamp valves can sometimes be difficult to see so take a good look.
- Get something insulated and when the amp is running, tap each valve in turn . Set the volume to halfway, This will let you hear if they are microphonic. If a valve is noisy it will get worse with tapping.
- There are some other things to do but if you are new to valve amps, then this is enough testing at this point.
Finally….
I hope this quick guide is helpful. I have kept this as a simple guide. So it should only be used as a first look. Keep in mind that there can be up to 800 volts inside your amp and the amp can hold on to the volts for days. There is a real risk to your health if you touch a live connection. TAKE CARE!!
We have a whole range of valves available in our shop and please email us ( info at valvetubeguitaramps dot com) and we are always happy to answer questions.
