Buying power tubes and interpreting Tube data. Gm vs Mu does anyone understand this stuff.

kipple

I want to buy some power Tubes and My goal is to buy power tubes that have the earliest breakup so they have more distortion/clipping.

So.... I would like to be able to have an understanding of the test data on power tubes that some sellers provide so I can know if I am buying suitable tubes.

Just To be clear this is NOT about me wanting to know how to achieve more Gain 

What I want is to know how to interpret the Tube Test Data

So far I only have a VERY basic understanding of some stuff and need some help . 
So far as I understand and please correct me if I am wrong ..I understand that.

Gm is Transconductance 
Mu is amplification or tube gain factor.

So what would this tube Data below indicate .. Would the tubes be High Transconductance early breakup or late breakup
 60 ma at 12 ma/v GM.
The tubes are Mullard EL84

 As I understand it and again someone please correct me if I am wrong .. It is High Transconductance or Gm that  = Early  breakup.

But.... I do not know how to interpret the data that some tube sellers provide to be able to understand if The tube has high transconductance or early breakup .

So... can anyone tell me please is there any simple easy way to interpret tube data to be able to understand if a tube has High Transconductance or early breakup..
Early breakup being the main goal...

Also Do I need to factor in how the different types of data such as Gm Mu relate to each other to understand if a tube will have early breakup ?

Does anyone here know this stuff.

Thanks Ian

Plectrum

What you actually need are higher gain pre-amp valves (not 'tubes'!!!!) to drive the power stage harder. Or just stick a clean boost pedal in front of the amp.

kipple

Plectrum said:

What you actually need are higher gain pre-amp valves (not 'tubes'!!!!) to drive the power stage harder. Or just stick a clean boost pedal in front of the amp.

No..
What I Actually need is specifically what I have described and asked for help with ....Which is Knowledge of how to interpret power Tube test data 
Tube dealers will supply on request tubes that have early break up and tube dealers use the Tube test data to determine which tubes break up earlier and.....
I would like to know how to interpret that test Data for myself. 

The whole point of this post is for someone to help me understand how to interpret the tube test data..

If I just wanted more gain I would of ASKED how do I get more gain what pedal pre amp tubes etc.
But I didn't ask that.

RiftAmps

TC, MU and Gm are of little use to you, and unfortunately you've bought into some 'internet wisdom' that doesn't really apply in our fun little world of low-fidelity guitar amplifiers. It's just a sales tactic to make you buy from a certain seller over another.....I wish I came up with that one!

Any amp-tech worth his salt can bias ANY matched set of power valves for 'early' breakup, or max power and clarity if you wish. The Gm, MU and TC numbers are irrelevant and are of only use for matching.

hywelg

OP is right pre amp gain and power stage breakup are entirely different things. 

Wish I knew too so I'm subscribing. 

And also info on preamp valve data too. Matched triodes are important in certain applications and I'd like to know what data are important for a good match. (Dumble clone PI position needs a well matched pair of triodes)

ICBM

hywelg said:

Matched triodes are important in certain applications

But none of them are in guitar amps .

Actually not quite true any more - the new miniature amps like the Blackstar HT-5 and the Marshall 1W series which use a dual triode as the power valve will benefit from a matched valve, in the same way as matching separate power valves.

hywelg said:

(Dumble clone PI position needs a well matched pair of triodes)

Bear in mind that the standard long-tailed-pair phase inverter circuit - which is usually held up as where you 'need' or 'can benefit from' a matched valve - is *inherently* mismatched, and hence using a matched valve will not produce a matched output.

I seem to remember that Dumble used a trimmer in the circuit to allow it to be balanced more accurately, but I could be wrong.

kipple

RiftAmps said:

TC and Gm are of little use to you, and unfortunately you've bought into some 'internet wisdom' that doesn't really apply in our fun little world of low-fidelity guitar amplifiers. It's just a sales tactic to make you buy from a certain seller over another.....I wish I came up with that one!

Any amp-tech worth his salt can bias ANY matched set of power vlaves for 'early' breakup, or max power and clarity of you wish. The Gm and TC numbers are irrelevant and are of only use for matching.

I understand that biasing an amp hotter or colder can affect the amps performance but....
I do not believe for one second that all power tubes are the same or that they all all have the same characteristics .

Some power tubes naturally break up earlier than others and some power tubes have to be pushed MUCH harder before they break up .
I do not need to be an amp tech to I know what my ears tell me

I have two Identical amps and two sets of power tubes..
One set of the power tubes breaks up way earlier than the other set no matter which amp I put them in.
One set of power tubes has a naturally lower current draw when I measure cathode current and that is the set that breaks up early...

I have also observed this in other amps over the years .. Some power tubes stay much cleaner than others do and other tubes get dirty at much lower volume

I have requested power tubes from dealers e.g. watford valves that break up early and when I have received them then made direct comparisons and it is fact some power tubes break up earlier than others ... It is not 'internet wisdom'

Watford valves are perfectly capable of selecting power tubes with early or late break up and have done so MANY times for me and presumably they are using test data to select the tubes as they cannot be just guessing because they always get it right .If I ask for early break up they pick them correctly and If I ask for Late breakup they select them correctly.

I just want to know what contributes to this and if there is some way of telling for myself from test data. 

hywelg

ICBM said:

I seem to remember that Dumble used a trimmer in the circuit to allow it to be balanced more accurately, but I could be wrong.

Correct, but for best results you not only need to balance the PI using the trimmer you also need an inherently balanced valve. 

Some techniques for measuring 'balance' actually take into account power valves as well though I don't think that's imperative. 

ICBM

hywelg said:

Correct, but for best results you not only need to balance the PI using the trimmer you also need an inherently balanced valve.

Presumably because otherwise it can be outside the range of the trimmer.

hywelg said:

Some techniques for measuring 'balance' actually take into account power valves as well though I don't think that's imperative. 

It would be essential. It doesn't matter how well-balanced the PI is if the power valves then aren't.

This is also something that probably only matters for hi-fi.

RiftAmps

kipple said:I understand that biasing an amp hotter or colder can affect the amps performance but....
I do not believe for one second that all power tubes are the same or that they all all have the same characteristics .

Not all valves are created equal, correct. I didn't say that they weren't.

Circuit designers know this fact, and that's why we ensure that there is a way to adjust the operating conditions of the valve to achieve the desired result.

kipple said:

Some power tubes naturally break up earlier than others and some power tubes have to be pushed MUCH harder before they break up .
I do not need to be an amp tech to I know what my ears tell me

I have two Identical amps and two sets of power tubes..
One set of the power tubes breaks up way earlier than the other set no matter which amp I put them in.
One set of power tubes has a naturally lower current draw when I measure cathode current and that is the set that breaks up early...

I'm sure that they do, but a correctly designed circuit will allow for these differences to be dialled out, ensuring consistent performance.

If however, you have an amplifier that either a)doesn't have adjustable bias or b)is self regulating, then the differences between valves become more apparant because you're no longer optimising the performance.

kipple said:

I have requested power tubes from dealers e.g. watford valves that break up early and when I have received them then made direct comparisons and it is fact some power tubes break up earlier than others ... It is not 'internet wisdom'

Sure it is. You won't find this in the old textbooks or any academic papers.


The Gm, MU, and TC numbers given by testers are the results obtained by testing the valve under certain conditions (usually those stated on the datasheet). I can tell you now that those numbers will change when plugged into your amp.

kipple

RiftAmps said:

kipple said:I understand that biasing an amp hotter or colder can affect the amps performance but....
I do not believe for one second that all power tubes are the same or that they all all have the same characteristics .

Not all valves are created equal, correct. I didn't say that they weren't.

Circuit designers know this fact, and that's why we ensure that there is a way to adjust the operating conditions of the valve to achieve the desired result.

kipple said:

Some power tubes naturally break up earlier than others and some power tubes have to be pushed MUCH harder before they break up .
I do not need to be an amp tech to I know what my ears tell me

I have two Identical amps and two sets of power tubes..
One set of the power tubes breaks up way earlier than the other set no matter which amp I put them in.
One set of power tubes has a naturally lower current draw when I measure cathode current and that is the set that breaks up early...

I'm sure that they do, but a correctly designed circuit will allow for these differences to be dialled out, ensuring consistent performance.

If however, you have an amplifier that either a)doesn't have adjustable bias or b)is self regulating, then the differences between valves become more apparant because you're no longer optimising the performance.

kipple said:

I have requested power tubes from dealers e.g. watford valves that break up early and when I have received them then made direct comparisons and it is fact some power tubes break up earlier than others ... It is not 'internet wisdom'

Sure it is. You won't find this in the old textbooks or any academic papers.


The Gm, MU, and TC numbers given by testers are the results obtained by testing the valve under certain conditions (usually those stated on the datasheet). I can tell you now that those numbers will change when plugged into your amp.

Ok ...
So how are Watford valves selecting Power tubes with early break up ? 

They must be using a method it cannot just be guess work,.
If you do not know the answer then that is fine just say you do not know ..

P.S. All My amps are fixed bias with a Bias trimmer pot

ecc83

If you need a spark plug for your engine it does not matter whether you buy a Lodge, Lucas or any other brand SO LONG AS IT IS IN SPECIFICATION. Same goes for wheel bearings. Valves are the same. The published data for gm, mu and Ra are characteristics OF THAT VALVE. If an EL84 e.g. were far enough out of that specc' to 'sound' differently it should not be SOLD as an EL84 IMO!

There are valves, mostly Dble triodes that are made to a higher specc'. Harder vacuum, more rigid electrodes, purer materials but an 83 is an 83 is an 83! Mu is always 100 and pro-rata for the other parameter (which are related BTW like Ohms Law) .

Re balance? I have probably balanced more 12BH7s than anyone else here (of about 3 different 'makes') and I never needed more than the merest 1/2 turn of the balance pot.  I would guess in many amps the bloody anode loads would be further out of tolerance than most PI valve samples. (that's assuming they are right to start with and not 82&100k!)

I will agree that modern power valves vary greatly in their bias point for a particular Ia but that's coz they's mostly ***T.

Dave.

ecc83

"It would be essential. It doesn't matter how well-balanced the PI is if the power valves then aren't."

Well IC, the power valves MIGHT be oobalance 'the other way' and cancel the PI problem! (ok, just being a PITA!)

Dave.

kipple

How do companies like Watford Valves select on request for their customers Power tubes with early breakup...
Does Anyone Know ?

RiftAmps

kipple said:

How do companies like Watford Valves select on request for their customers Power tubes with early breakup...
Does Anyone Know ?

Well, the article on his website reads like an advertisement with just enough jargon to confuse the average punter. He offers no real technical information on the equipment and processes that he uses - https://www.watfordvalves.com/output_valves.asp

I would hazard a guess that any valves which don't test as 'strong' are then offered as 'early breakup', rather than having to return them to his supplier.

ICBM

ecc83 said:

"It would be essential. It doesn't matter how well-balanced the PI is if the power valves then aren't."

Well IC, the power valves MIGHT be oobalance 'the other way' and cancel the PI problem! (ok, just being a PITA!)

Ha .

Actually, there is one thing I have come across which does illustrate exactly that, possibly…

If I'm working on an old Marshall, I check the idle current in both (or all four) power valves, and put the ones with the lower draw on the side of the power amp nearest the PI valve, which is the one receiving signal from the first side of the LTP. This both reduces the visible stress (excessive screen glow) on the valves on this side when the amp is driven hard, and also seems to make the amp sound better.

This is presumably because this side of the PI is capable of driving the power valves slightly harder than the other side, so you can offset that by choosing power valves which are further down their load line… although I'm happy to admit that there isn't much science behind it, and I did it originally to reduce the stress on the valves rather than anything to do with the sound.

kipple

RiftAmps said:

kipple said:

How do companies like Watford Valves select on request for their customers Power tubes with early breakup...
Does Anyone Know ?

Well, the article on his website reads like an advertisement with just enough jargon to confuse the average punter. He offers no real technical information on the equipment and processes that he uses - https://www.watfordvalves.com/output_valves.asp

I would hazard a guess that any valves which don't test as 'strong' are then offered as 'early breakup', rather than having to return them to his supplier.

Or Maybe.... companies like watford just realise there is a market for those tubes with Buyers like myself who are obssesed with the way a set of power tubes will sound and perform and would prefer power tubes tubes with early break up.

This is not snake oil..or 'internet wisdom' there are definitely power tubes that break up earlier than others and that is what I want but I want to be able to buy them from sellers on places like Ebay from sellers who are not like Watford but are just enthusiasts or smaller companies and have test data. I want to know how to use the data so I know what I am buying.. 

 Ok. So.... How do I use test data to tell the difference between what you described as 'Strong' or 'weak'  What should I be looking for. 
For example
What would this data  below indicate ..

 60 ma at 12 ma/v GM.
The tubes are Mullard EL84
What does the 60 ma mean ? is the Mu or RP rp or something else also 12ma/v GM is that high GM ?

I have bought tubes from Groove tubes in the past that use what they describe as Fine scale.
Fine scale is 1-10 and tubes in 1-3 scale are described as early break up and they always are compared to tubes 4-10 scale.

Tubes I have received in 1-3 which are early breakup always seem to have a naturally lower current draw /cathode current and the rest of the scale are later breakup and have higher current draw.
There is obviously a method here I just want to know If I can understand it.
If I can then I can look at tubes that are being sold with test data and figure out if they are early break up.

I see tubes on ebay all the time with test data that are being sold by sellers that are not from companies Like watford or groove tubes but are being sold by what I would think are just enthusiasts But I have NO Idea what the test data means and I would like to be able to make an informed decision when deciding whether or not to buy. But I cannot as I know Jack about what the data means.. 

Sassafras

I'd just use an overdrive pedal.

ecc83

"This is not snake oil..or 'internet wisdom' there are definitely power tubes that break up earlier than others "

Agreed but 'breakup' is just a euphemism for 'distortion'! Morgan Jones in his 'Valve Amplifiers' gives the results of a huge number of tests on a selection of triodes. The distortion variation is greatest between types but there is still some variation frm sample to sample. But, Jones's data is very well ordered and reported and is just for triodes! The valves were all used in a specific circuit and at specific values of Ia and Va . The input drive voltage was constant for all tests as was the load involved .

Imagine trying to get similar data from a batch of power pentodes? Va supply would have to be regulated (and very low ripple) . Then the tests done at a specific Va, Vg2 and Ia and load resistance. Frequency(s)? ! Having obtained all this data, how does the punter know how it translates to HIS amplifier? Changing Ia to the design value might be quite easy but Va/Vg2 not so and if the OPTraff has a different ratio? All bets are off.  I also cannot see how the tester could get away with LESS than THE best, 'hi fi' OPT he can find because of the vast variation in the gitamp market, i.e. using a Mesa 50W traff would not be the same as using a Blackstar HT-60 traff.

But what is the supplier of these valves got to give the customer? After all this selection work (and I have done some, a lot less comprehensive and it is a Fkn lot of work I can tell thee!) "There you go chaps! These valves I am ripping you off for are WORSE than the stock samples"!

Dave.

RiftAmps

kipple said:

RiftAmps said:

kipple said:

How do companies like Watford Valves select on request for their customers Power tubes with early breakup...
Does Anyone Know ?

Well, the article on his website reads like an advertisement with just enough jargon to confuse the average punter. He offers no real technical information on the equipment and processes that he uses - https://www.watfordvalves.com/output_valves.asp

I would hazard a guess that any valves which don't test as 'strong' are then offered as 'early breakup', rather than having to return them to his supplier.

Or Maybe.... companies like watford just realise there is a market for those tubes with Buyers like myself who are obssesed with the way a set of power tubes will sound and perform and would prefer power tubes tubes with early break up.

This is not snake oil..or 'internet wisdom' there are definitely power tubes that break up earlier than others and that is what I want but I want to be able to buy them from sellers on places like Ebay from sellers who are not like Watford but are just enthusiasts or smaller companies and have test data. I want to know how to use the data so I know what I am buying.. 

 Ok. So.... How do I use test data to tell the difference between what you described as 'Strong' or 'weak'  What should I be looking for. 
For example
What would this data  below indicate ..

 60 ma at 12 ma/v GM.
The tubes are Mullard EL84
What does the 60 ma mean ? is the Mu or RP rp or something else also 12ma/v GM is that high GM ?

I have bought tubes from Groove tubes in the past that use what they describe as Fine scale.
Fine scale is 1-10 and tubes in 1-3 scale are described as early break up and they always are compared to tubes 4-10 scale.

Tubes I have received in 1-3 which are early breakup always seem to have a naturally lower current draw /cathode current and the rest of the scale are later breakup and have higher current draw.
There is obviously a method here I just want to know If I can understand it.
If I can then I can look at tubes that are being sold with test data and figure out if they are early break up.

I see tubes on ebay all the time with test data that are being sold by sellers that are not from companies Like watford or groove tubes but are being sold by what I would think are just enthusiasts But I have NO Idea what the test data means and I would like to be able to make an informed decision when deciding whether or not to buy. But I cannot as I know Jack about what the data means.. 

Those numbers are irrelevant. It's like a car magazine saying "We've tested this car and it can hit 60mph. We've also tested another car and it can also do 60mph"

Great...but without knowing the exact test conditions used, that number is useless and offers no insight into the true performance of the car.

In order to understand the data figures given by the vendor, you need to know the following information and cannot draw any conclusions without them:

• Make/model of tester (I have three valve testers, and each give different readings)
• Anode Voltage (Va)
• Anode Current (Ia)
  
• Anode Resistance (Ra)
• Control grid bias voltage (Vg1)
• Screen Grid voltage (Vg2)
• Screen Grid current (Ig2)
• Are Pentodes actually tested as Triodes (some testers do this)
  

Now, to make things even more complex, some valve testers will apply the same test conditions to each valve and report the result, whilst others will vary the test conditions in order to achieve the same result. Comparing results from one type of tester to another is again, pointless. Are you sure that the eBay sellers use the same equipment and test conditions as Watford?

ICBM

Also bear in mind that Watford are the company that sell "cryogenically treated" valves for some ridiculous mark-up...