unmatched tubes

[tubeToaster]

I have a bunch of unmatched EL84 tubes and was wondering if I could use them in my lite IIb if I have separate cathode caps and resistors on each EL84 .

Thanks, Dave

[CurtissRobin]

Matching tubes is not dogma. They don't HAVE to be matched and matched pairs don't necessarily sound better than unmatched. As long as your cathode resistor is reasonably-sized (i.e. is close to Marshall's original value) I'd recommend plugging in two EL84s and playing. Then change one of them and play again. Repeat until you've found a combination that stands out from the others. Set that pair aside and do the exercise again to find a second good pair. Put the rest on the shelf until you feel like doing it again.

You can look at this as a time burner or you can use the time to work on your scales and etudes while sorting tubes. Frankly, I consider this a much better approach than going by meter readings.

KennyO

[stevesuk]

I have spent a lot of time lately on producing output transformers, researching opinions and myths , talking to different engineers etc.
Hand finishing them by the dozen and testing them.

One thing that strikes me is tube matching is tied up with push pull OT matching !!

Unless the OT is wound with the two anode windings exactly matched then it is always slightly out of balance. So why bother to match tubes.

One of the ways to reduce mismatch in an OT is to wind the windings next to each other. If they are wound on top of each other they are going to be naturally mismatched. Different length of wire, further from the core etc.
Some Hi-Fi OT's are parallel wound, (bifilar type) but AFAIK most guitar OT's are not.
It is an expensive way of winding, so most do not !!

The other thing I will start a separate thread (and probably an argument) on is, some OT's are LOUDER than others. Several Engineers have confirmed what I hear.

Steve UK

www.valvepower.co.uk

[tubeToaster]

Thanks for the quick replies. I guess mismatched tubes are more of an issue in fixed bias amps than in cathode bias amps.

Guess I'll put a random pair in and check that one or the other is not biased to hot and long as I like the sound I'm good to go.

Thanks, Dave

[zaphod_phil]

Even in fixed-bias amps they can be OK, as long as they aren't too far out from each other. I have a recently-built fixed-bias amp with me right now that's happily running with a couple of different sets of non-matched tubes, without any problem.

[tubeToaster]

Even in fixed-bias amps they can be OK, as long as they aren't too far out from each other. I have a recently-built fixed-bias amp with me right now that's happily running with a couple of different sets of non-matched tubes, without any problem.

Cool ! I'll have to try that in my fixed bias amp also .

[rjgtr]

The only issue with non-closely matched tubes is one of wear. If they are too out of balance they will wear unevenly. One may pull so much more that it red plates. Anything within 10-12ms should be ok.

[CurtissRobin]

The only issue with non-closely matched tubes is one of wear. If they are too out of balance they will wear unevenly. One may pull so much more that it red plates. Anything within 10-12ms should be ok.

I'll buy into "wear unevenly" but redplating in one of a pair indicates an extreme (all caps and underscore "extreme" and throw in "extremely rare") mismatch. Push-pull power amplifiers were around and working well for decades before tube matching meant anything to anyone outside a laboratory.

I'd think fixed bias would make mismatches more apparent than cathode bias, but only a little.

KennyO

[rjgtr]

I'll buy into "wear unevenly" but redplating in one of a pair indicates an extreme (all caps and underscore "extreme" and throw in "extremely rare") mismatch.

Yes, I agree it would be rare. But if the tubes are mismatched enough it can happen. In either fixed or cathode biased situations, current is going to seek the path of least resistance. If one tube is offering that path it can get to the point it draws too much current and red plates. This is why it is smart to keep an eye on a new pair of tubes - just in case.

[Alexo]

I've seen it happen too. I know push-pull amps were around before the modern matching mania, but there was some matching in the old days, or so I'm told - the techs would try to find the pair that canceled the most hum, which, while unscientific, can get your tubes in the right ballpark.

[leslie]

I have spent a lot of time lately on producing output transformers, researching opinions and myths , talking to different engineers etc.
Hand finishing them by the dozen and testing them.

One thing that strikes me is tube matching is tied up with push pull OT matching !!

Unless the OT is wound with the two anode windings exactly matched then it is always slightly out of balance. So why bother to match tubes.

One of the ways to reduce mismatch in an OT is to wind the windings next to each other. If they are wound on top of each other they are going to be naturally mismatched. Different length of wire, further from the core etc.
Some Hi-Fi OT's are parallel wound, (bifilar type) but AFAIK most guitar OT's are not.
It is an expensive way of winding, so most do not !!

The other thing I will start a separate thread (and probably an argument) on is, some OT's are LOUDER than others. Several Engineers have confirmed what I hear.

Steve UK

www.valvepower.co.uk

Of course, the theory is mind game but in practic everything reacts to something.
Really, action/reaction concept or if we don't want to investigate particular matter-phenomena.
Ingo have on his website interesting image about many (known) interactions/variables inside OT
... it would be shame not to post it here...
Transformer explained as RLC circuit.

many interesting PDF files on this link http://www.ig-transformatoren.com/gener ... nical.html