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Post new topic Vacuum tube 'rating'
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Author Topic:  Vacuum tube 'rating'
Dave Meis


From:
Olympic Peninsula, Washington, USA
Post  Posted 9 May 2019 7:30 pm    
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I'm assuming they're talking about earlier or later breakup? What does the scale actually refer to, and which end of the scale would be 'clean' ? I guess the real question is: is this BS? Thanks!
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Bob Carlucci


From:
Candor, New York, USA
Post  Posted 9 May 2019 7:58 pm    
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Early Distortion # 1-3- is best for a softer attack, and those who play a lot of rock and blues solos.

Average Distortion # 4-7- is great for your normal all around tone - for those who want some versatility in their sound.

Late Distortion # 8-10- is chosen for those who want their sound dynamic and clean - especially Jazz and Bass players.

Basically, the higher the number, the less distortion at lower volumes..

ANY tube will break up when pushed hard enough.. As far as if its BS or not, only your ears will tell you for sure.. I never worried too much about ratings myself, but some tubes will distort earlier than others .. bob
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Dave Meis


From:
Olympic Peninsula, Washington, USA
Post  Posted 9 May 2019 8:25 pm    
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Thanks Bob!
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Godfrey Arthur


From:
The Bronx via the Philippines
Post  Posted 9 May 2019 11:25 pm    
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Tubes are funny devices in that depending on the circuit that any tube resides and the design of the use of any one tube by the circuit designer, since tube makers don't even give ratings for their tubes, for example emission, it is almost an illusion, that unless one understands the circuit from the standpoint of an electronics engineer and what each tube and what EACH section of the tube is supposed to be doing in said circuit, can one give a "rating."

And one must add to this that each tube should be tested for more than just "good or bad" ratings on a drugstore tube tester, getting into many other factors like Mutual Conductance Values (Gm) and a host of other tests for accuracy and all this hinges on having one expensive laboratory grade tube tester.

So rating a tube appears to be more of a marketing ploy rather than anything based in reality because the best tube tester after all the types of tube testers ever made, is the circuit itself that the tube is going to be used.


Amplitrex tube tester going for $3,000

And one can't test everything about a tube on just one tester. There are other models/brands of testers needed to do a better test job.

Point being, what are the chances the people giving ratings of tubes have these testers, know how to use them and what to look for on a tube going into a Twin reverb?

There are cheap testers made decades ago by Heathkit, Micronta (Radio Shack) EICO that are "emmissions only testers" and these although can tell if the tube is working or not, will not give enough accurate information in order to "rate" a tube for any specific purpose.



Although this looks cool and has many sockets for different tubes, it is still just an emissions only tester. Goes for about $100 on eBay. For testing a tube if it works or not.

In fact there is thought that using a simple tester can damage a tube. Oh Well

That, and all these tester makers made up their own values lists for specific tubes. So what may test high on one tester, will test low on another.

So where is the accuracy?


Hickok 539B, the better tester needed together with the Amplitrex, goes for $500 with the upgraded LED meters, calibrated and serviced.

As Bob succinctly pointed out "only your ears will tell you for sure" and that is the best judge as tube rollers have come to learn.

Your amp will have different tubes in there and all those together make up a different salad of tones. So how can anyone "rate" a tube when there are so many other factors to consider?

Sometimes a cheap non-descript tube will do wonders in the right position in the circuit, and no one can really tell us why.

Tubes are funny devices!

If one is on the hunt for the Grail of tubes, one has to spend the time and money and do this for every amp they own.

Expect to make a mini-career of it.
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Dave Meis


From:
Olympic Peninsula, Washington, USA
Post  Posted 10 May 2019 7:56 am    
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Thanks Godfrey!
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ajm


From:
Los Angeles
Post  Posted 10 May 2019 8:17 am    
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Stop.
Time out.

The only POWER tubes that I know of that were "rated" are/were Groove Tubes.
I believe that GT went out of business and may have been sold in some fashion (to Fender maybe?).

Are GT still available where you can select the rating, or do they only make one type/rating now?

Are there other power tubes that use the same or a similar rating?

Dave: What brand/type of tubes are you asking about?
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Godfrey Arthur


From:
The Bronx via the Philippines
Post  Posted 10 May 2019 9:01 am    
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ajm wrote:
Stop.
Time out.

The only POWER tubes that I know of that were "rated" are/were Groove Tubes.
I believe that GT went out of business and may have been sold in some fashion (to Fender maybe?).

Are GT still available where you can select the rating, or do they only make one type/rating now?

Are there other power tubes that use the same or a similar rating?

Dave: What brand/type of tubes are you asking about?



Yes Groove Tubes did put out this claim.

The Fender tube scale is
Blue = GT 1-3 range
White = GT 4-7 range
Red = GT 8-10 range




But what is this list based on and how accurate is any of it to be able to generalize a specific tube will work across the board for any/all amps?

What happens when the preamp tubes are of all different types, brands, years and how do the myriad of preamp tubes drive the power tubes and in what amp circuit?

Too much to claim with something so arbitrary and dependent on so many factors.

Granted someone went through the trouble of making this list, but how can they guaranty it will work in your amp the way they claim?

Even the more experienced tube tester repair people say the best test is the amp/circuit itself.

A tube will behave different in so many different circuits, even if the circuit is the same between two amps of the same make and model since even the amps themselves don't sound the same.

That's like saying "buy this microphone and you will sound like Dio or Merle Haggard."

If you read forums where tube rollers post, they all have different ideas of what any one single tube does and they mostly have different amps they are using them in.

Interesting discussion (the tube roller forums) but I don't think a consensus can be reached.
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Greg Lambert


From:
Illinois, USA
Post  Posted 10 May 2019 9:52 am    
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Heres a pretty good comparison chart

https://www.amplifiedparts.com/tech-articles/12ax7-comparison-current-made-tubes
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Dave Meis


From:
Olympic Peninsula, Washington, USA
Post  Posted 10 May 2019 11:30 am    
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My original question was: what is the 'rating' system.. what values do they actually refer to. The question WAS INDEED sparked by looking at GT tubes, but that made me curious about the data used. Seems we all agree that the ears are the final arbitrator, which made me wonder .. if they're looking at a wave form on an isolated piece of equipment, it probably means LESS than nothing in actual application. On the other hand, if it helps someone make a valid decision.. cool!
I'm a hopeless tube roller myself. I've gotten used to being surprised at how good or bad tubes of various reputations actually SOUND when I put them in my amps.
Thanks to all!
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Michael Butler


From:
California, USA
Post  Posted 10 May 2019 2:46 pm    
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groove tubes did sell to fender. i went to the closeout sale in san fernando, ca. got the tube amp book signed by aspen pittman along with a bunch of tubes.

perhaps, "rating" in your eyes, dave, is what a lot of tube sellers do and call it matching. that, i believe, is a little more along with what godfrey is indicating.

note that the rca tube manual states that the real true test of a tube is in the circuit, not in a tester. i have a cheap tester but i really only use it to see if the tube works or not and to check for shorts. then it goes in the circuit and i either subjectively like it or not.

play music!
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Dave Meis


From:
Olympic Peninsula, Washington, USA
Post  Posted 10 May 2019 9:00 pm    
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Thanks Michael... I understand the 'matching' , but was curious about the '1-10' thing. I hadn't heard of that, and was wondering what it meant. I didn't see how that figured in. Very Happy
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ajm


From:
Los Angeles
Post  Posted 11 May 2019 7:18 am    
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From what I recall, one of (if not THE) main selling points of the GT rating system was to enable the average Joe to replace his tubes without re-biasing.

If you initially had your amp set up and biased for, say, a GT 6L6 with a rating of, say, #7, then you could simply buy another set of the same rating and just plug them in.

In theory I suppose it would work.
But it's probably too much trouble trying to find another set of the same rating.
And don't discount the marketing aspect of this whole thing, either.

This was back in the 70's-80's. All of this biasing and rating stuff was sort of new to the average musician. And tube quality was down for a few years also, which didn't help.

After a while amps started to appear with test points and adjustment pots on the back, along with instructions on biasing in their manuals.
While basic electronics are still probably out of the range of understanding of most people, things as a whole are much easier than they were.
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