Repairs

Amplifier Repair FAQs

Do I need to replace my valves?

Power Valves - The amp will give out noticeable and unpleasant tones/white noises and will be reduced in power, the glow that a bad valve gives off may be different in colour, intensity or gone altogether. The valve may show signs of overheating which can be seen if the writing on the valve has faded. If the vacuum is compromised you will see that the top of the valve has a white deposit. For an amplifier that is regularly used, say 1 gig / rehearsal per week, I would recommend replacing power valves annually. Power valves should be replaced as a matched set.

Pre-Amp Valves – You may notice a general drop in tone quality. Pre amp valves may go ‘microphonic’ where you will hear a slight squealing, there is no visual indication, combos are more likely to suffer from this. For an amplifier that is regularly used, say 1 gig / rehearsal per week, I would recommend replacing power valves every 3 years. Pre Amp valves have more impact on the tone qualities of your amp so you may choose to swap tubes to find ‘your’ tone. Pre amp valves may be replaced individually. 

Do my power valves need biasing?

Depends on what amplifier! As a general rule of thumb, amplifier types which use EL-84 power valves are self biasing or cathode biasing (not in all cases). Other types (EL-34, 6L6, KT88 etc) will require biasing.

Why do my valves need biasing?

Biasing adjusts the grid voltage, this is basically speaking the idle voltage of the valve. We can bias to your requirements, hot, regular or cool.

Hot: Earlier Distortion – Marshall territory.
Cool: More clean headroom – Fender land.

If you replace valves without biasing, you may have the following problems.
Too hot - If the voltage is too high the amplifier runs hot, gets more full sounding then harsh, shorter tube life, will be noisier. It's like a car with the idle racing, you need to keep your foot slammed on the brake.

Too cool - Sluggish, weaker sounding, can lack sparkle, tubes last longer but amp doesn't respond as well. It's like a car that is barely running, step on it and it wants to die or never really responds like you would want it to.

Why do my power valves need to be matched?

Because they are all doing the same job at the same time so they need to be in unison.

Why don’t my pre amp valves need matching?

Because they are carrying out different tasks, for example an amplifier may have the following:

V1 - First gain stage
V2 - Second gain stage
V3 - Phase inverter
V4 – Reverb driver (not strictly a pre amp tube)
So, you may mix and match brands to suit your own tone requirements (we can offer advice). 

What about rectifier valves?

Generally speaking, if your rectifier valve is shot you will be blowing fuses. However, if you are going for a full re-valve I would replace the rectifier valve.

How long does it take?

We do not generally hold stocks of valves so if you require this service we need to order the valves to your requirements, a deposit covering the cost of the valves may be required. So please allow a week for delivery.

Can I change valves myself?

If you have no experience of working with valve amplifiers we strongly advise that you do not. Valve amplifiers operate at high voltages and currents that have the potential to injure and kill, even when the amplifier is switched off (the electrolytic filter capacitors can hold a lethal charge for a considerable time).

I’ve bought valves, can you fit them for me?

Yes, but for power valves, only if they are a matched set.

Can you check the bias on my already fitted valves?

Yes, we can check your bias and advise on any action required.

Anything Other Questions? Just ask!

Other Work

Speaker replacement
Amplifier repairs
Amplifier modifications
Scratchy potentiometer cleaning