Matched/biased tubes

[richard parker]

When did we start worrying about having properly matched and biased tubes ? What were guys doing in the fifties/sixties when they needed to replace tubes ?

I first had tube amps in the mid seventies. Any problems and we'd throw in whatever tubes we could get hold of. No-one knew anything about matching and biasing. I don't remember having any problems.

 

[Edgecrusher]

Re: Matched/biased tubes

This came about in the 80's largely thanks to Aspen Pittmann of Groove Tubes. Your right in the past people would just use whatever tubes not only that but it wasnt uncommon for people to only replace a faulty tube not a whole set. In the case of a severe mismatch there might be some extra noise and hum from the amp but thats about it. Though something to keep in mind too though is that the tubes from the 50's and 60's were much much better with much better quality control than today. I've bought bulk EH 12ax7's before out of 100 around 40 were either dead or completely unusable. The worse the tolerances for the tubes are the more important bias and matching becomes. Take Mesa for example they test tubes to their own standards if you have a mesa amp and you buy mesa tubes its a plug and play deal. Sadly times have changed and the golden age of tube electronics is long over. These days I dont think I would consider using an untested tube or swapping power tubes without rebiasing.

 

[Simon_F]

Re: Matched/biased tubes

I first had tube amps in the mid seventies. Any problems and we'd throw in whatever tubes we could get hold of. No-one knew anything about matching and biasing. I don't remember having any problems.

That's my memory too! I don't remember anyone replacing tubes as a maintenance activity. If an EL34 died you went to an electrical shop, bought an EL34 (any EL34...) and stuck it in the amp. Good to go!

Having said that, "any EL34" was probably a Mullard that is still working fine today.

 

[Jeremiah]

Re: Matched/biased tubes

Maybe someone somewhere will see all these threads on forums about how the tubes you get now don't have the same level of quality control/durability as they had in the 50s, and maybe try to actually make some the same standard.

You would think the market would be there; sure tubes aren't used in every piece of electronic gear like they were back in the day, but there seem to be a lot of tube guitar amps getting built and a lot of people buying and swapping tubes.

Other components like guitar amp specific speakers still seem to be getting made to as good a standard as they ever were, so why not tubes?

 

[wahwah]

Re: Matched/biased tubes

Maybe someone somewhere will see all these threads on forums about how the tubes you get now don't have the same level of quality control/durability as they had in the 50s, and maybe try to actually make some the same standard.

It would be great, but it won't happen, for a variety of reasons. 50's manufacture and production was prior to the cynical concept of planned obsolescence, where items are made to fail in order to move more units. The tubes made in the 50s were made to last, because the market was so widespread that there were still ample profits, and the idea was to make them as good as they could possibly be. Quality control standards were higher. There is also the fact that many of the components and materials that helped make those tubes what they were, can no longer be legally used in production. With these things considered, along with the fact that the market is really only guitar players and audiophiles, the cost of producing tubes of that quality would be prohibitive, possibly even exceeding the cost of vintage tubes.




Cheers..................................... wahwah

 

[richard parker]

Re: Matched/biased tubes

So is the consensus of opinion that older tubes, being better quality, didn't NEED to be matched or biased ?

 

[Edgecrusher]

Re: Matched/biased tubes

So is the consensus of opinion that older tubes, being better quality, didn't NEED to be matched or biased ?

Matched no. biased... maybe depends

 

[Edgecrusher]

Re: Matched/biased tubes

Maybe someone somewhere will see all these threads on forums about how the tubes you get now don't have the same level of quality control/durability as they had in the 50s, and maybe try to actually make some the same standard.

You would think the market would be there; sure tubes aren't used in every piece of electronic gear like they were back in the day, but there seem to be a lot of tube guitar amps getting built and a lot of people buying and swapping tubes.

Other components like guitar amp specific speakers still seem to be getting made to as good a standard as they ever were, so why not tubes?

Speakers are still a current technology item. Tubes are obsolete in any area other than guitar amps and audio enthusiasts. A lot of the know how in tube manufacture has been completely forgotten its not only that the materials are no longer available but they dont know how they used to do it. Many of the techniques were proprietary many of the materials are proprietary and the people with that knowledge are long gone.

Keep in mind that the golden age of tubes was the 1950's even by the 60's the transistor started to creep in and tube quality was past its zenith. A lot of the tubes that people pay big money for as vintage from the 70's are junk. Particularly the ones labeled "JAN" which were designed for military equipment not audio usage (ok some are alright but many are not worth the prices they command)

You wont see a truly high quality tube ever again. The market is too small noone would pay the price that could cover the production cost. This is why I have stashed away enough EL34's 6L6's 5881's for me to have good tubes for what should be the rest of my lifetime. I'm glad I got hot on NOS tubes in the mid 90's and early 2000's before the prices skyrocketed to what they are today.

 

[misterwhizzy]

Re: Matched/biased tubes

Sadly times have changed and the golden age of tube electronics is long over.

Sadly is a relative term, though. Think about what you're typing your messages on.

 

[Chickenwings]

Re: Matched/biased tubes

you still need to play the right note at the right time. that hasn't changed.

 

[Scott_F]

Re: Matched/biased tubes

Militaries on both sides needed and demanded high quality tubes.. Days gone by. Matching is easy now. Biasing mandatory in my book unless cathode biased.

Back then, this phrase applies. "What you don't know, you just don't know."

 

[aleclee]

Re: Matched/biased tubes

This is why I have stashed away enough EL34's 6L6's 5881's for me to have good tubes for what should be the rest of my lifetime. I'm glad I got hot on NOS tubes in the mid 90's and early 2000's before the prices skyrocketed to what they are today.

This is (part of) why I went digital.

 

[Gearjoneser]

Re: Matched/biased tubes

I think the amp companies back then took care to bias tubes exactly where they should be, and if nobody tampered with the bias pot then it stayed in normal range. It's also a reason why people used to say one amp sounded better than another. They may have been comparing amps with bias drift, mismatched or worn tubes to ones that were serviced.

Nowadays, they seem to purposely bias on the cold side, just to avoid returns and warranty claims just because of tubes. The first thing I do with a modern amp is check the bias.

 

[Edgecrusher]

Re: Matched/biased tubes

It's also a reason why people used to say one amp sounded better than another. They may have been comparing amps with bias drift, mismatched or worn tubes to ones that were serviced.

Your definitely spot on here, I bought my first Marshall a 50 watt JMP in 1989 for 350 bucks with cab cause the music store couldnt sell it cause sound wise it was a dog. I took it to a local church organ repair man who "fixed" it for me. This is where I learned of bias he told me then that a lot of guys would take an amp that the bias had drifted on then "sprinkle holy water" on it to wow their customers with how great their amp now sounded.

 

[Dr. Vegetable]

Re: Matched/biased tubes

From an electrical standpoint, the purpose of bias is to center your signal voltages in the linear range of operation for the tube. A properly biased tube will operate the closest to "ideal" with minimal distortion. Matched tubes have been measured and paired to find ones that will have similar bias points. If you get matched tubes, you are more likely to be able to swap tubes and still be at/near the correct bias point.

Some circuit designs (such as a push-pull amplifier) need matched components because one transistor amplifies the negative portion of the waveform while another does the positive portion. If the two components do not have similar electrical characteristics, the circuit response will not be symmetrical and you would get a different kind of distortion. I don't believe push-pull is a common configuration in tube amplifier circuits, though. The individual tubes generally work in successive gain stages, so strict matching may have less importance when using tubes together in an amp. (Please, someone with more tube amp knowledge correct me!)

Of course, not all distortion is "bad" distortion, and the effects of a slightly incorrect bias setting will be subtle, so 'back in the day' people didn't worry too much about this. I've swapped tubes in a pinch without setting the bias, and nothing caught fire or sounded like poo-poo. It is very possible that we heard the subtle distortion caused by our mal-adjusted '60s era tube heads and thought it sounded "cool" and "organic."

If you are on a quest for the cleanest of the cleans, you probably do care about these details. Otherwise it may not be so critical.

 

[Edgecrusher]

Re: Matched/biased tubes

Tons of amplifiers are class AB class AB2. (AKA push pull) I find even in these circuits that having a tube mismatch is either negligible or can add a nice texture to the amp. The fact of the matter is that tube electronics in many areas are pretty forgiving and have a wide range of operating tolerances.

 

[Scott_F]

Matched/biased tubes

I was laughing looking at the tweed tremolux layout sheet from way back when. "Voltages +/- 20%" written on there. That's a pretty big range. THAT'S why some old amps sounded better than others if you ask me. Resistor values were all over the place. I doubt when Leo and the boys grabbed a 1K5 resistor in the old days they actually checked the impedance. They just grabbed and soldered as fast as they could. Just my opinion.

 

[Dr. Vegetable]

Re: Matched/biased tubes

I was laughing looking at the tweed tremolux layout sheet from way back when. "Voltages +/- 20%" written on there. That's a pretty big range. THAT'S why some old amps sounded better than others if you ask me. Resistor values were all over the place. I doubt when Leo and the boys grabbed a 1K5 resistor in the old days they actually checked the impedance. They just grabbed and soldered as fast as they could. Just my opinion.

Right, which is why it was all the more important to set the bias points in those circuits.

One odd thing about inexpensive (low-tolerance) resistors is that they are guaranteed to be somewhat out of tolerance. This is because of the way resistors are manufactured. They make them, then measure the resistance in order to mark them for sale. If a resistor is within 1% of a certain stock value, it is marked as "high precision" (gold band) and sold at a premium. The ones that fail this test, but that are within 5% get the next level of tolerance (silver), followed by the low tolerance 10% components. This means that a 10% resistor is almost guaranteed to be at least 5% out of whack from the resistance value marked on it.

But whatever - it's obviously close enough for rock and roll.