Valves

All work that requires the replacement of valves or biasing should be carried out by a qualified engineer.

What do the different valves in my amplifier and combo do?

Most of our units contain a mixture of valves responsible for preamp or the power amplifier. The number and type varies from one amplifier to another.

The preamp valves take the small guitar signal and amplifies and also alters its gain and tone. It then feeds the larger signal to drive the power valves.

The power valves feed the larger signal to drive the speaker through the output transformer.

Some of our transistor units have an ECC83 valve in the preamp to add tone and colour to the signal.  

What does the term bias mean?

In simple terms, the bias is an electrical current that must be at the optimum setting to ensure that your power valves run efficiently. If you don’t have your amplifier re-biased then you run the risk of too much or not enough voltage being supplied to the valves. This can cause damage to both the valves and the amplifier itself.

Can I remove two valves from my 100 watt to make it a 50 watt?

This amplifier is designed to work with four power valves and we would advise you not to remove any of the valves as it will cause damage. If you would like to reduce the output of the amplifier then use a power soak. This lowers the physical output and lets you turn the amplifier higher to achieve the tone you want.

If you would like to buy a 50 watt then check out our product section on this website for more information.

Does fitting old valves make my amplifier more or less reliable. Will my amplifier sound better?

Its best to replace old valves with good quality new ones and old valves like Mullard should only be used if you know and trust their history. The tone and quality varies from valve to valve and there is no guarantee that old valves sound better than new ones.

Can I put different types of valves in my preamp to alter the tone or volume?

Preamp valves should always be replaced with the same type and model. Using a different type or model will damage your amplifier.

Can I put different types of power valves in my amplifier?

Power valves should ways be replaced with the same type and model. All power valves should be replaced at the same time. Your amplifier will also need to be re-biased to match the new valves.

Can I mix the types/models of power valves to give a different sound?

We do not recommend mixing the power valves as this will damage your amplifier. Always use the same type and model and ensure they are replaced at the same time.

Why are my valves glowing blue/purple?

Valves glowing in this way are not necessarily faulty but it is best to have it check by a qualified engineer.

When and how should I change my valves?

Power valves should be replaced every 18 months to 2 years and all valves should be changed at the same time. The amplifier should then be re-biased.

Preamp valves should be replaced every 4 years and can be replaced individually. The amplifier won’t require biasing after this.

Does altering the bias change the sound of my unit or how long the valves last?

Setting the bias value too high or low will alter the sound but it will also shorten the life of your power valves and damage your unit.

What is the difference between a 12AX7 and an ECC83?

The term 12AX7 is the American model number for the ECC83.

What is the difference between a 6L6 and a 5881?

The 5881 is the same type of valve as the 6L6 but with slightly higher output. The bias on the amplifier will need to be set specifically for 5881 or 6L6 valves.

Can I mix different EL34 power valves and will this alter my sound?

Like all other power valves you should replace them all at the same time with the same type and model. Mixing power valves will damage your unit.  

Will using a power soak affect the life of my power valves?

Using a power soak may shorten the lifespan of your power valve because you are driving the amplifier harder and louder.

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