FYI tube matching etc...

[ZootHornRollo_dup1]

copied this from the fender forum from a thread titled "enough is enough" here's an excerp.

In my shop, betwwen myself and my amp tech Russ, we repair dozens of tube amps a month. Between him and I, we share about 55 years of collective experience servicing, modifying, and building amps, and we've come to these conclusions:

 

1) Matched power tubes, in the end, don't mean squat.

 

2) The whole tweaky current method of biasing is inherently flawed.

 

Let's talk about #1: OK, so the tube supplier of your choice has weeded out the suckers, matched the tubes for transconductance, and did a 24-hour burn-in.

 

Does anyone realize that transconductance can suddenly shift permanently while a tube is under stress? Or that they often change their transconductance at different rates? Does anyone realize at all that as a tube wears, it loses transconductance?

 

We've checked power tubes for transconductance after being pounded a few days. Goodbye matched rating! Amp still sounds good, though.

 

You are worried about balance on both halves of the push-pull swing in the amp? I'd worry about the phase-inverter before I worried about the power tubes. Phase-inverters, whether they are Split-Load or Schmitt ("Long-Tailed") are inherently unbalanced in their drive capabilities. Attempts have been made to achieve symmetry by adding trimpots or voltage dividers, but you can't change facts: in a Long-Tailed PI, you have two distinctly different amplifier types at work (common-cathode/common-grid) that have different drive capabilities, thus different output impedances, and they will never match. The common attempt to match them is by using 82K and 100K resistors on the plates to achieve signal symmetry, but then you have unbalanced DC operating voltages. A compromise.

 

In the Split-Load type, you are driving on side from the plate (common-cathode amp; lots of gain available) and one side from the cathode (cathode follower; a gain of 1 at most, i.e. output = input). Once again, two different amp types with two different source impedances, once again, a compromise.

 

And all this time, there are your nice, matched power tubes, faithfully reproducing the inherent non-linearities, and there isn't a damn thing you can do about.

 

Until Groove Tubes and MESA/boogie started matching power tubes, you got what you got when you bought them. GE, RCA, Philips. Put 'em in, make sure the bias voltage was within the accepted 20% tolerance, and off you went, another good-sounding amp.

 

Does anyone REALLY believe that life began with Groove Tubes? Or, did the marketing hype create the market itself?

 

There were great-sounding amps long before tube matching was even a concept.

 

There's A LOT of latitude in the operating parameters of tube amps. It's the nature of the beast. Don't worry so much about matched tubes, it's not as critical as you think.

 

Of course, just KNOWING that you have matched tubes might make everything sound better already, without even turning the amp on.

 

Basic Marketing Psychology 101, in it's purest form.

 

BTW- I've checked "matched pairs" from many different notorious suppliers, and they ain't always what they say they are!

 

Thought you might like to know that.

 

2) Biasing is something that is necessary to make a tube work. There are really no absolute values. In fact, many power tubes are rated in the tube manuals for Class A, AB1, and AB2 operation. There's a WIDE range between Class A and AB2 that are acceptable operating parameters. I tend to bias the towards AB1, to minimize crossover distortion at full RMS output. The "milliamp tweaks" would find the current too high, and back it down to where they should be. I've done this, and most times, it results in crossover distortion. I watch the signal on the scope, plus I use a distortion analyzer. I bias by the look of the waveform, and ONLY THEN will I check the bias voltage, just as a reference point. This method is totally legitimate, and until the industry got "tweaky", was the widely accepted method.

 

Apparently, someone found the old method flawed and had to reinvent it, as if what Fender, Marshall and Ampeg did was just not good enough.

 

Until this happened, cathode current was only a reference spec addressed solely by the amp and tube designers. Now, all of a sudden, it's the friggin' Holy Grail!

 

The old method still SOUNDS the best. Yes, it might shorten the tube life slightly to operate at somewhat increased current. But when did we stop worrying about sound, and start worrying about numbers? Why not just channel that energy into playing, and forget about the damn amp if it sounds good?

 

Am I an old warhorse? Yes, most definitely! But, then again, tube amps are old warhorses too, and should be treated as such.

 

OK, I've said MY piece, so go ahead and let me have it! I'm ready!

[ZootHornRollo_dup1]

no responses eh? ... for all the talk around here re: tube matching and phase inverters etc...

well ok.

[Wickerman]

Well, I'm not experienced or knowledgeable enough to argue but I'll keep ordering my matched tubes and wait for Myles to say something smart and tart! (I'm retarded)

[Rick Huff]

Mr Rollo,

 

Debate is a good thing. We should never stop wanting to mix it up. Also, there's quite a number of people out there who have lots of experience with tubes. I'm not convinced we have all the parameters necessary to quantify tube performance. Today, I was talking to a friend who was marveling over his favorite pair of 6l6's which were not nearly as close as some his other pairs yet they sound perceptibly better. This occurrence happens often to be sure.

 

Rick@Skyway

[myles_rose]

Originally posted by ZootHornRollo:

copied this from the fender forum from a thread titled "enough is enough" here's an excerp.

In my shop, betwwen myself and my amp tech Russ, we repair dozens of tube amps a month. Between him and I, we share about 55 years of collective experience servicing, modifying, and building amps, and we've come to these conclusions:

 

1) Matched power tubes, in the end, don't mean squat.

 

2) The whole tweaky current method of biasing is inherently flawed.

 

Let's talk about #1: OK, so the tube supplier of your choice has weeded out the suckers, matched the tubes for transconductance, and did a 24-hour burn-in.

 

Does anyone realize that transconductance can suddenly shift permanently while a tube is under stress? Or that they often change their transconductance at different rates? Does anyone realize at all that as a tube wears, it loses transconductance?

 

We've checked power tubes for transconductance after being pounded a few days. Goodbye matched rating! Amp still sounds good, though.

 

You are worried about balance on both halves of the push-pull swing in the amp? I'd worry about the phase-inverter before I worried about the power tubes. Phase-inverters, whether they are Split-Load or Schmitt ("Long-Tailed") are inherently unbalanced in their drive capabilities. Attempts have been made to achieve symmetry by adding trimpots or voltage dividers, but you can't change facts: in a Long-Tailed PI, you have two distinctly different amplifier types at work (common-cathode/common-grid) that have different drive capabilities, thus different output impedances, and they will never match. The common attempt to match them is by using 82K and 100K resistors on the plates to achieve signal symmetry, but then you have unbalanced DC operating voltages. A compromise.

 

In the Split-Load type, you are driving on side from the plate (common-cathode amp; lots of gain available) and one side from the cathode (cathode follower; a gain of 1 at most, i.e. output = input). Once again, two different amp types with two different source impedances, once again, a compromise.

 

And all this time, there are your nice, matched power tubes, faithfully reproducing the inherent non-linearities, and there isn't a damn thing you can do about.

 

Until Groove Tubes and MESA/boogie started matching power tubes, you got what you got when you bought them. GE, RCA, Philips. Put 'em in, make sure the bias voltage was within the accepted 20% tolerance, and off you went, another good-sounding amp.

 

Does anyone REALLY believe that life began with Groove Tubes? Or, did the marketing hype create the market itself?

 

There were great-sounding amps long before tube matching was even a concept.

 

There's A LOT of latitude in the operating parameters of tube amps. It's the nature of the beast. Don't worry so much about matched tubes, it's not as critical as you think.

 

Of course, just KNOWING that you have matched tubes might make everything sound better already, without even turning the amp on.

 

Basic Marketing Psychology 101, in it's purest form.

 

BTW- I've checked "matched pairs" from many different notorious suppliers, and they ain't always what they say they are!

 

Thought you might like to know that.

 

2) Biasing is something that is necessary to make a tube work. There are really no absolute values. In fact, many power tubes are rated in the tube manuals for Class A, AB1, and AB2 operation. There's a WIDE range between Class A and AB2 that are acceptable operating parameters. I tend to bias the towards AB1, to minimize crossover distortion at full RMS output. The "milliamp tweaks" would find the current too high, and back it down to where they should be. I've done this, and most times, it results in crossover distortion. I watch the signal on the scope, plus I use a distortion analyzer. I bias by the look of the waveform, and ONLY THEN will I check the bias voltage, just as a reference point. This method is totally legitimate, and until the industry got "tweaky", was the widely accepted method.

 

Apparently, someone found the old method flawed and had to reinvent it, as if what Fender, Marshall and Ampeg did was just not good enough.

 

Until this happened, cathode current was only a reference spec addressed solely by the amp and tube designers. Now, all of a sudden, it's the friggin' Holy Grail!

 

The old method still SOUNDS the best. Yes, it might shorten the tube life slightly to operate at somewhat increased current. But when did we stop worrying about sound, and start worrying about numbers? Why not just channel that energy into playing, and forget about the damn amp if it sounds good?

 

Am I an old warhorse? Yes, most definitely! But, then again, tube amps are old warhorses too, and should be treated as such.

 

OK, I've said MY piece, so go ahead and let me have it! I'm ready!

I find more than one comment here funny, but I will limit this to:

 

"There were great-sounding amps long before tube matching was even a concept".

 

If you think back, there were also a lot of them of the same model that had hum from unbalanced output sections, amps that failed in a few hours due to grid leakage of new tubes (which were better back then also), and the continuing issue of "this Deluxe sounds really great, and that one sounds just okay".

 

If you think its all hype, that's fine .... but here are a few folks that don't, who by the way, pay for their tubes, as GT does not give anything away for free unlike some other folks ....

 

Billy Gibbons (Z.Z. Top) Raven Gysr (Top Dead Center) Eddie Kramer (Producer)

Eddie Van Halen (Van Halen) John Jorgensen Lenny Kravitz

Robben Ford (Robben Ford) Freddy Cannon Steve Tyler (Aerosmith)

Jerry Donahue (Hellecasters) Kenny Rankin Michael LLoyd (Producer)

Eric Johnson (Eric Johnson) Roberta Flack Steve Stills (Crosby, Stills & Nash)

Michael Jackson Jeffrey Osborne Blink 182

Jimmy Vaughan (Jimmy Vaughan) Lou Rawls Tom Petty (Tom Petty)

Larry Carlton (Larry Carlton) James Ingram Mike Campbell (Tom Petty)

Dickey Betts (Allman Brothers) Steve Vai Howie Epstien (Tom Petty)

Warren Haynes (Allman Brothers) Daniel Edwards Stan Lynch (Tom Petty)

Robert Cray (Robert Cray) Eric Clapton Slash (G.N.R. & Slash's Snake Pit)

Jimmy Page (Led Zeppelin) Henry Mancini Gilby Clark (G.N.R.)

Roy Thomas Baker (Producer) Terry Evans Keith Scott (Brian Adams)

Jeff Baxter (Doobie Brothers) Myron Grombacher (Pat Benetar) Brian Adams (Brian Adams)

Steve Miller (Steve Miller) Dann Huff John Mellencamp (John Mellencamp)

Bush Melissa Manchester Moody Blues

Prince (Paisley Park Studios) Jimmy Stewart Jon Anderson (Yes)

No Doubt Willie Nelson Jackson Browne

Carlos Rios (Whitney Houston) Paul McCartney David Lindley (Jackson Brown)

Courtney Love Spinal Tap Black Crows

Joe Perry (Aerosmith) Barry Manilow Lynyrd Skynyrd

Mick Jagger (Rolling Stones) Billy Nedley Los Lobos (Caesar Rojas)

Keith Richards (Rolling Stones) Merry Clayton Damon Johnson (Brother Cain)

Ron Wood (Rolling Stones) Hank Williams Jr. Jeff Healy (Jeff Healy Band)

Phil Alvin (Blasters) Irvin "Magic" Johnson Brian Setzer (Brian Setzer Orchestra)

Angus Young (AC/DC) Ice T Stanley Clark

Malcolm Young (AC/DC) Neil Sedaka Pearl Jam

Big Head Todd & The Monsters Bugs Henderson Stone Temple Pilots

Kathy Mattea Belinda Carlisle Motley Crue

Clint Black (Clint Black) Sly Georgia Satellites

Pete Anderson (Dwight Yoakam) Scream Studio Steve Stevens

Stevie Wonder T.G. Sheppard Joe Satriani

Dave Navarro Lee Pepper Sound Studios Dave Marshall

Mike Rutherford (Genesis) Frank Sinatra Adrian Belew

Darryl Stuermer (Genesis) Ocean Studios Pete Townsend

Jay Mascus (Dinosaur Jr.) Shirley Jones George Lynch

Michael Nesmith (Monkeys) Neverland Productions Peter Buck (R.E.M.)

Mark Knopfler (Dire Straits) Tony Orlando Dave Amatto

Steve Hackett Medicine Wheel Jennifer Batten (Michael Jackson)

Ted Nugent Connie Stevens Roger Fischer (Heart)

Little Feat (Bill Payne & Paul Barrere) David Harris The Ramones

Scorpions Keith Brown The Beastie Boys

Queensryche Maria McKee (Lone Justice) Red Hot Chili Peppers

The Muffs Billy Davis Jr. Danny Gill

Paul Reed Smith Simple Minds Goo Goo Dolls

Oak Ridge Boys John Tillotson Kiss

Jake E.Lee Warrant Ben Harper

Slaughter Debbie Boone Sheryl Crow

Helmet Tool Slayer

Skid Row Pat Boone Mavericks

Smashmouth Journey Rembrandts

Noel Roy (Laurie Morgan) Mary Hart Counting Crows

Tommy Hannum (Ricky Van Shelton) Buddy Guy Garbage

Amy Grant Brian Hyland Garth Brooks

Dolly Parton Carlene Carter Brooks & Dunn

Reba McIntyre Dokken Sammy Hagar

Kent Wells Randy Bachman Buck Owens

Robbie Krieger Coverdale/Page Michael Sembello

Johnny Winter Tesla Cranberries

The Outlaws Cracker Weezer

Ry Cooder Ugly Kid Joe Antharax

Boyz II Men Cinderella John Fogerty

Elliot Easton Bob Golub (Rod Stewart) David Lee Roth

Bonnie Raitt Andrew Burns Asleep At The Wheel

Jimmy Buffet Boston B-52s

Bad Company Shania Twain Filter

Greg Martin (KY, Head Hunters) Buck Dharma (Blue Oyster Cult) Darin Scott (Spiderbabys / Belledonna)

David Gilmour (Pink Floyd) Bodeans Jody Whitesides (Amalgam / Solo artist)

Johnny Lang Rudy Guess (Carole King) Jason Orme (Alanis Morrisette)

Zakk Wylde John Griswald (Janet Jackson) Our Lady Peace

Snoop Dogg Billy Sheehan Mike Tempesta (Powerman 5000)

The Eagles The Calling The Doors

Omnibus Seapods Beck Ani DeFranco

Andy Summers Seal Lindsey Buckingham

 

For some of the other factors:

 

Analyzing and Selecting tubes.

 

We literally go through thousands of tubes, rejecting more tubes than we accept. We put every tube through a rigorous performance test, one at a time, in real amp circuits. The preamp tubes are rejected for adverse microphonics, low output or high noise. Power tubes are more involved, and they go through additional analysis. Here's what we're looking for:

 

Grid Leakage. Causes tube to burn out quickly, and worse yet, to short out and wreak lots of havoc. We throw these tubes out.

 

Weak Vacuum. Tube will act deceptively normal, then just burn out on you (usually at the worst time!). These tubes don't make it past the first round.

 

Gain to Distortion Ratio. The center of all Groove Tube magic! This measurement tells us if the tube will distort early or later in its power range. Since the tube distortion is rich in harmonics (That's why we love 'em!), the tonality of each tube will vary according to this ratio. Only Groove Tubes sets have been measured and matched to insure longer sustain, wider frequency response and a more musical amplifier!

 

More than just Great Tone.

 

The Groove Tubes Process produces many welcomed improvements:

 

Dramatically Improved Sustain by eliminating phase cancellation (which occurs when dissimilar tones coming from unmatched tubes are combined and cancel out certain frequencies.)

 

Improved Harmonic Balance- All the notes you play will have the same amplitude. (No more dead spots or dull notes!)

 

Longer Life Span by 1st) eliminating faulty tubes. 2nd) Our balanced sets reduce stress that occurs when a stronger tube is working too hard to make up for its weaker partner, and 3rd) because our sets drive the output transformer evenly it actually runs cooler!

 

.... So .... when I see so much writing by somebody like you, I have to take a bit of time to do a bit of writing, cutting, as pasting myself, so you get both sides of the story.

 

You also may be one of those folks that think all the tubes are exactly the same, not realizing that there are specific contracts with specific makers in place.

 

Just in case you think all tubes from a given manufacturer are the same ....

 

12AX7C - China, new tooling with a few spec changes specific to GT.

 

12AX7R - Russia, Reflector Factory, east side of the Reflector factory where the Sovtek 12AX7WA/WB is made.

 

12AX7R2 - Russia, Reflector Factory, on the west side of the factory where the Sovtek 12AX7LP/LPS are made.

 

12AX7R3 - Russia, Reflector factory, west side, new tooling, same as the Electro Harmonix (sold by Sovtek in their EH division ... and Sovtek is not a tube company, but a NYC company doing business with Reflector) This is the same as the 12AX7EH.

 

12AX7A - no longer in stock, the USA 12AX7 tube that used to be at a higher retail than the other 12AX7's.

 

ECC83 - from the JJ factory

 

7025 - from the Ei factory

 

12AT7Y - Ei

 

12AT7C - China

 

(by the way, on the latest GT pricelist, there is a legend at the bottom where they tell where the tubes are from country wise)

 

12AU7 - Ei

 

6V6R - a newer Russian 6V6 that is from the same tooling as the Electro Harmonix 6V6.

 

6V6C - a new 6V6 off new tooling that is holding up to higher plate voltages nicely and has a sound more folks are starting to prefer than the 6V6R.

 

6L6CB - Chinese, softer vacuum, coke bottle shape.

 

6L6B - Russia, Reflector, sometimes called the Sovtek 5881. Sturdy tube, maybe the most strong from a physical standpoint, great for touring stuff that gets thrashed by heavy handed road crews.

 

6L6S - from the JJ factory but rebased and re-pinned if or when they come in with stamped pins with dipped pins that tear up some sockets. The rolled polished pins are also tapered. A bit of an extended midrange that a lot of heavy rockers love.

 

6L6R2 - The Svetlana 6L6, a tube I personally like a lot.

 

5881A - NOS, Tung-Sol - Great in Fender Black Face amps for a lot of my Blueprinting clients.

 

KT-66C - China, the KT-66 that folks like Valve Art and others sell as the KT-66.

 

KT-66HP - Russia, built under contract for GT to GT specs. A close copy of the GEC tube. Handles higher plate voltages than the KT-66C and has a different getter assembly. Great to 525 volts, and the tube the Dr. Z Route 66 was designed around.

 

6L6GE - made in California by the GT factory with USA parts and labor.

EL-34C - Chinese EL-34 (25 watt tube)

 

EL-34R - Reflector (Russian) EL-34 (25 watt tube) sometimes sold as the EH tube. Pretty linear and Mullard like in some aspects of its character.

 

EL-34R2 - Svetlana (Russian) 25 watt tube, used a lot as standard in Rivera amps. This is a stronger tube then the R or C.

 

E34Ls - JJ factory but with a GT developed heat sink assembly extruded onto the plate assembly. Hold up a JJ and a GT and tou can see the difference without any sort of equipment (with the naked eye its easy).

 

This is a 30 watt tube and bias should be checked and adjusted when one uses these. Very high output and strong mids. Used by Gibbons, Perry, Walsh.

 

6CA7 GE - the next USA tube on the GT list to go into production with a higher vacuum than the softer vacuum Europe style of tubes that use a diffusion pump for vacuum rather than a turbo-molecular pump in manufacture. ... also has an active beam forming assembly as a 6L6.

 

6550A - USA NOS GE no longer in stock.

 

6550C - Chinese and a fun tube, as you can get these to distort in amps where the 6550A would not.

 

6550R - Russian 6550, takes longer to distort than the Chinese, maybe somewhere between the A and C.

 

KT-88C2 - Chinese KT-88

 

KT-88-SV - JJ tube that has a different plate assembly with a large heat sink welded to the plate. It may have a different base, pins, at times if necessary.

 

EL-84R - Reflector Russia (as the Sovtek)

 

EL84Y - Ei

 

EL-84S - JJ

 

7027 - JJ

 

7591 - Reflector, Russia.

 

Long before I came to GT (May of this year), my own business referred folks to many great vendors, and my personal website still does. There are some great vendors out there, and a few really awful ones.

 

Regards,

 

Myles