kel84 valves

Im not going to ask which valves to use.

I have aquired a pair of mullard el84. Unfortunately 2 isnt enough. Before i go and buy 2 more is there an issue of them not being a quad set? The two i have came from an old stereo amp.

Also, what happens if i replace 2 valves? Ive no idea if using the mullards will make much difference, would having 2 different valves in each channel ruin the sound or give you an inbetween sound?

[Bizzie]

I would have thought that if you mix different manufacturers valves in the same amp the you will get distortion if you have one of each in each channel and a channel imbalance if you have one type in the left channel and a different type in the right channel but don't imagine that there would be any damage.

Yeah, i figured, was just curious.

[Greg.]

Hi Graeme,

In a push pull amp, the two output tubes (per channel) generally need to be matched/balanced. Retailers offer this as a generally free service. You can also get balanced quads if you're pedantic like me

Unbalanced performance can lead to unwanted hum and reduced performance. If you are buying more, you could try your old valves in one channel and the new in the other. It might work and save you shelling out for four all in one go. Having said that there is no reason why you can't experiment, mix them up and see how it sounds.

Best wishes,

Greg

[Mark]

I thought the valves in a KEL84 were 'self-balancing', so it wasn't necessary to buy matched valves ?

Mark

[JerryT]

Originally Posted by Mark

I thought the valves in a KEL84 were 'self-balancing', so it wasn't necessary to buy matched valves ?

Mark

Hi Mark

An analogy.

You can replace one tyre at a time on a modern car, using other tyres that are the right size and speed/load rating. The car will continue to function and much of the time you won't notice the difference - it may not feel quite as sharp/responsive/accurate/secure (choose your own adjective) but it will do pretty well. However there will come a point when the difference in performance cannot be overcome by the car's inbuilt correction factors (EBD, ABS, ASC, basic geometry etc.). At that point things will go badly wrong and you will notice it. Afterwards, when you replace the unmatched tyres with a matched pair of good quality, you will end up with a car that feels more consistent, delivers better performance/economy/handling (depending on which tyres you chose and why) and gives you more pleasure.

I'll leave people who live and breathe valve loadlines, Class A, AB and the 'servo action' of localised nfb to give you a better electronic explanation.

In short a matched pair is a sensible investment - like swapping both front tyres when one has a puncture and keeping the undamaged one as an emergency spare.

All IMHO

Jerry

[Richard]

Originally Posted by graeme

Im not going to ask which valves to use.

I have aquired a pair of mullard el84. Unfortunately 2 isnt enough. Before i go and buy 2 more is there an issue of them not being a quad set? The two i have came from an old stereo amp.

Also, what happens if i replace 2 valves? Ive no idea if using the mullards will make much difference, would having 2 different valves in each channel ruin the sound or give you an inbetween sound?

Hi Graeme,

The amp will self balance within reason. 10% match on current is usually acceptable but many used (and some new) examples will vary by more than this.

If you can get a few secondhand Mullards together and want them matching drop me a pm. Don't pay too much though unless they're tested/guaranteed as they tend to go low on the insulation - a lot of power from a small envelope.

Whatever, try and stick with 4 the same make. JJ and EI Yugo (a dead ringer for Mullards) test and sound good if buying new.

Rich

Thanks, will do.

[bearded fiddler]

Originally Posted by Greg.

Hi Graeme,

In a push pull amp, the two output tubes (per channel) generally need to be matched/balanced. Retailers offer this as a generally free service. You can also get balanced quads if you're pedantic like me

Unbalanced performance can lead to unwanted hum and reduced performance. If you are buying more, you could try your old valves in one channel and the new in the other. It might work and save you shelling out for four all in one go. Having said that there is no reason why you can't experiment, mix them up and see how it sounds.

Best wishes,

Greg

Hi Greg

Do you have any experience with EL84's from different manufacturers. I like the JJ Tesla and am now burning in a set of NOS military grade Russian valves by Reflector (not as smooth as the JJ's I think). What about Genalex Gold Lion, or any other make you like?

Regards