This short article deals with power valves for guitar amplifiers. There is another article which covers preamplifier guitar amplifier valves and also rectifier guitar amplifier valves. It is not intended to show you how tube amps work or the detailed operation of a tube amplifier.
There are only three basic types of guitar amplifier valves, although there are different makes (manufacturers) for each type.
The three types of guitar amplifier valves are:
- Preamplifier valves
- Power amplifier valves
- Rectifier valves
Briefly though, the power guitar amplifier valves do the ‘heavy lifting’ in the output stage of the amplifier. They supply the power which moves the speaker in and out.
Rectifier guitar amplifier valves are rare these days (as the silicon diodfe has replaced them) but purists like to keep their old rectifier valve in their vintage amplifier. All this valve does is to rectify the AC mains input to produce DC. This is FAR better done with silicon rectifier diodes these days and at a fraction of the cost. Very few new amps have rectifier guitar amplifier valves nowadays unless they are appealing to the ‘retro’ market.
These guitar amplifier valves are easily recognisable as they are the larger tubes in your amplifier. The smaller tubes are the preamplifier valves.
First you need to know that your guitar amplifier will either have two, or four output valves.
If it has two, then they work as a pair; one ‘pushing’ the loudspeaker cone, the other ‘pulling’ it. In technical terms, one valve handles one half of the sine wave (let’s say the top half) and the other valve handles the other half of the sine wave (say the bottom half). You may have heard of ‘push pull’ amplification and this is what’s going on here.
99% of all valve guitar amplifiers have this ‘push-pull’ arrangement of valves driven by the phase splitter valve.
Let me just briefly explain why an amplifier may have four output tubes instead of two.
In a 4-valve set up, the valves are just doubled up to give twice the power. E.g. a 2 valve amplifier will typically be 50W, whereas a 4 valve amplifier will be 100W. So two valves ‘push’ and the other two ‘pull’. All four are driven by a single phase splitter valve.
Which Power Valves Are Best?
Your amplifier will be designed to use one particular type of power valve. The vast, vast majority of amps use one of these power valves:
- The 6L6GC
- The EL34
- The 6V6
- The EL84
A few amps use the 5881 (you can use a 6L6 here instead see this article) or rarely, KT77.
As a general rule, don’t mess with the TYPE of power valve you put in your amp. If it takes a 6L6 (say) then that’s what you should use.
What about make?
My view is that you’d be hard pushed to tell the difference between MAKES of power valve. It’s very hard to do a proper A/B test in any event. I suggest you stick to a good quality, reliable and sensibly priced valve such as JJ.