Tube Mis-Matches - educate me please

[OlinMusic]

I know all the talk of YOU MUST HAVE MATCHED SETS and BIAS YOUR AMP CORRECTLY!

I have 3 JJ Tesla's out of 4 (one broke long ago) sitting around. I wanted to try some different power tubes in one of my amps so I yanked 2 and put these in - it sounded WAYYYYYYY BETTER!

I will admit the amp smelled and felt a little hotter in the back, is it just me? I dunno.

Is this a horrible no no? Can I put the third JJ in and put a groove tube from another set in and ride this? Do I need to rebias? ALL I can tell you is I much prefer JJ's in general.

Educate me on matched sets etc etc.

 

[OlinMusic]

Re: Tube Mis-Matches - educate me please

BTW I found this post on an Audiophile forum

How audible tube mismatch is depends on a number of factors. These factors include your sensitivity to hearing distortion, the amplifier design and the power you demand of the amplifier relative to its nominal output capability. Amplifiers that allow one to adjust the bias current can minimize some of the effects of tube mismatch.

In addition to audible distortion severe tube mismatching can lead to tube or amplifier failure. Years ago when I attended flea markets (swap meets) it was not uncommon to see an old stereo amplifier with three old output tubes and one new tube. The reason the person was selling the amplifier is that one of the original old tubes had failed and the owner had replaced it with a single new tube. The new tube when matched with old tubes would draw much more current and quickly fail. The owner would then decide that it was not worth buying another new tube to replace the new one that had failed, so off to the flea market he would go to unload his problem on someone else. If all the tubes sharing a common cathode resistor had been replaced the premature tube failure would likely have been avoided. Of course the other common reason output tubes fail in old amplifiers is that the coupling capacitors become leaky and cause a destructive bias voltage to be applied to the output tube’s grid.

 

[kmcguitars]

Re: Tube Mis-Matches - educate me please

^^Good Post^^
You want matching tubes in your amp much the way you want matching tires on your car. If one tire one your car is to small, The car isn't going to drive right. It will wear faster and maybe cause damage some where in the drive train. Same thing with Tube Bias. When you put air in your tires it may look right? But a simple test with a tire pressure gauge will let you know if the tire is properly inflated to the manufacturer's specs. That's exactly why you want to have your bias checked. You want to be sure the tube are operating in range.

 

[OlinMusic]

Re: Tube Mis-Matches - educate me please

Ah, GREAT ANALOGY
I mean that put the "anal" in "analogy"

Now, what about biasing? Because lord knows, my tire pressure is never perfect. Can I stuff in a new set relatively safely without biasing them?

 

[kmcguitars]

Re: Tube Mis-Matches - educate me please

Now, what about biasing? Because lord knows, my tire pressure is never perfect. Can I stuff in a new set relatively safely without biasing them?

Tubes, Depending on the vendors Idea of what a `Matching set' is? Can vary a few mA + or - and still be considered matching. So that's why I avoid the word `Perfect'. The magic word is `within range':13:
In most cases you can stuff a new set of tubes in without biasing them. But if your asking if it can be done safely? If safely means knowing for certain?
Then you must check your bias.

 

[Gearjoneser]

Re: Tube Mis-Matches - educate me please

It's a good idea to own a bias tool, which I prefer in mA. Then, you put that bias tool socket in between the tube and amp, and adjust the bias pot so 6L6's are around 32-35 mA and EL-34's are around 36-40mA. The most proper way to do it is with an oscilloscope, so you can make sure there's no crossover distortion. I guess they try and get the sine wave to be perfect, when the bias is right on the money. By ear and sight, you can get it within range. With a bias tool you can get it close to perfect. With an oscilloscope, you can get it dead center.

 

[Robert S.]

Re: Tube Mis-Matches - educate me please

You can use different pairs of tubes in an amp but it's not the best idea to use mis-matched pairs. It lowers the efficience of the mis-matched pair.

Think of mayched pairs as a tug-of-war. One side pushes while the other side pulls. When both sides push and pull to the same strength, everything balances out. when one side is more efficient, which is what tube matching really rates, things are not quite equal. While a mis-matched set is not the end of the world, it isn't optimul either.

More important is bias. If your tubes are not properly biased, the will either run cold which will rob you of tone or they will run hot, again robbing you of tone and a too hot bias will dramatically decrease tube life.

You can run the teslas with an additional substitute tube but make sure your bias is correct or you'll be circle filing the teslas well before their normal life-span.

 

[OlinMusic]

Re: Tube Mis-Matches - educate me please

You can run the teslas with an additional substitute tube but make sure your bias is correct or you'll be circle filing the teslas well before their normal life-span.

What does that mean?

BTW I relented and called Eurotubes. Debated between the E34Ls and KT77's and we decided that since I do NOT need more lows, to go with the E34L, though the KT is verrrry intriguing.

Jay, at Euro, told me it's soooo easy to Bias an amp that I should learn. I bought a multimeter from them and he is sending instructions.

 

[The Golden Boy]

Re: Tube Mis-Matches - educate me please

Think of mayched pairs as a tug-of-war. One side pushes while the other side pulls. When both sides push and pull to the same strength, everything balances out. when one side is more efficient, which is what tube matching really rates, things are not quite equal. While a mis-matched set is not the end of the world, it isn't optimul either.

I think it was taught to me as a push/pull situation- like two people on a teeter-totter (or see-saw). If those two people are mismatched (IE one weighing 50 pounds more than the other) one is going to do a lot more work and it's not going to be a lot of fun for either party involved.

 

[Robert S.]

Re: Tube Mis-Matches - educate me please

running tubes too hot burns them up.

The circle file is a trash can.

 

[aleclee]

Re: Tube Mis-Matches - educate me please

The most proper way to do it is with an oscilloscope, so you can make sure there's no crossover distortion. I guess they try and get the sine wave to be perfect, when the bias is right on the money. By ear and sight, you can get it within range. With a bias tool you can get it close to perfect. With an oscilloscope, you can get it dead center.

It might be "most proper" but I figure the best way is to bias it 'til it sounds right to your ear and then just check to make sure it's in range.

My Dad's stories about electrical engineers like him advocating SS over tubes for audio "quality" taught me to trust my ears more than an oscilliscope.

 

[shredaholic]

Re: Tube Mis-Matches - educate me please

I wouldn't worry too much about matching tubes exactly, a bit of mismatch sounds good as you get more 2nd order harmonics in your tone. Anything past 10mA difference is probably bad news though. One cool thing I've got in my amp now is a bias mod kit from London Power, which allows you to adjust the bias current for each EL34 independently, and has multimeter jacks and bias pots mounted on the chassis so you can adjust the bias without having to open up the amp!

Soon I'm gonna try installing different tube types, ie. 2 6CA7's and 2 E34L's, as the multiple bias adjusts make that possible and safe. I love the fact that when a tube goes now I can just plonk another single tube in there without having to lay down cash on a set.

 

[Soujurn]

Re: Tube Mis-Matches - educate me please

Biasing an amp sometimes means sticking your hands around dangerous voltages. Before plunging ahead please learn the right way to work on live electrical circuits that have the potential to kill you!

This will naturally depend upon the type of amp.

One of my amps, the Peavey Classic 30 you don't have to worry about the bias at all.
But with my '66 Bassman head you do.

 

[OlinMusic]

Re: Tube Mis-Matches - educate me please

Yeah, my Framus has a bias pot on the rear outside