A little more information

The two main activities in my life: Helping the hungry in the late hours of the night and helping guitar players sound better one amp at a time.

I always try to remember that in order to do good one has to take action and actually do something.

I was born and raised in Los Angeles. I have watched the city and Southern California change for well over half a century.

I can be found on facebook at www.facebook.com/mylesr or on twitter at www.twitter.com/myles111us or on my own Guitar Amplifier Blueprinting website at www.mylesrose.com

Los Angeles Architectural History

Los Angeles Architectural History
1935 Art Deco at some of its finest: No. 168 - Griffith Observatory- (click on the photo for information)

Monday, March 25, 2013

"Genalex" Gold Lion 12AX7 / ECC83




Some of you have been asking if I could make some of my tube testing available again.  This is the first report that I have put out to the public for a while.  I will continue to put reports on this blog.

To see the full report just click on "read more" below

I will open by saying that "reissue" tubes generally do not have any similarities to the originals.  The exception to this was tubes made a few years back by Aspen Pittman at what was Groove Tubes.  The 6L6GE, 6CA7GE and 12AX7M tubes were what I termed "NVM", new vintage manufacture.  Aspen had procured the original design drawings and went as far as having the original mica producer make the original mica pieces.  If the plate material called for five clad formulation he followed this to the letter.  One cannot compare the product that Aspen produced with the "reissue" tubes out there today.

It is a matter of paying a bit of money to buy the rights to use a name on a product that is no longer in production or for that matter, no longer a company.

Here is one more offering today that I feel (my opinion) is one more evolution of a tube via a new label and gold pins.  As a side note, it costs VERY little to add gold pins to a tube.

All current production tubes seem to share one common trait.  Inconsistency.  This tube is no exception.  When I was at Groove Tubes their reject rate on average for preamp tubes in their gold series was 50%.  That was on a good day.  Some batches of Ei were as high as 90%.  

This B759 Genalex tube is one of the most pricey new production tubes.  Is it any better?  Well, that is a personal question when it comes to sonic quality.  Looking at some of the reviews done by others it seems that a lot of folks are drinking the koolaid.  I don't look at sonic qualities.  I look at data.  From a sonic point I do look at background noise, how fast a tube compresses and the curve traces for linearity.  

Measured observations were taken with 50 tubes which came from five vendors in batches of ten.  The tubes were tested and returned with the test data.  The ten tube test below was the BEST of the five sets.

The average gain was <82.  Not a surprise.  Typical range today is 80-85 out of an expected 100.  This is actual gain in circuit using design spec 12AX7 parameters which one can find on any 12AX7 data sheet.  These specs were minimums in the past which is one reason that tubes pulled from amps made in the fifties or sixties generally test better than new tubes today and still exceed the original design spec.

Average transconductance was 1573 out of 1600.  On paper it looks great.  On a typical GOOD / BAD tube tester or one that measure mutual conductance the tube would test nicely.  In reality the plate resistance was improper so the gain was low.  Looking at tube #1 we have 2420 which would look like an amazing tube.  Really gainy right?  Nope.  Plate resistance should be 62.5k.  At 35.1k our gain is nothing special.  The low plate resistance does provide a rise in plate current, just the thing I like to see for phase inverters, but unfortunately when the design parameters are this far out of balance the tube is just a piece of lackluster junk.  That 0.8 measurement below the 1.6?  That is the B side of the dual triode.  So much for a phase inverter.

OA tolerance?  The spread from high to low range in a specific design attribute.  We are looking for low numbers here.  Tubes from the past show less than a 5% spread.  Our plate current spread here was over 108%  

Plate current.  Remember Telefunken long smooth plates?  They did not always meet design spec.  It was typical of see plate current numbers of 0.8 and TC/MC number of 1200 rather than 1600.  BUT .... their plate resistance was 100k rather than 62.5k and all parameters were held in balance.  They had a true gain in excess of 100 and were the most gainy and articulate tubes out there.  HiFi folks loved them.  Due to the high gain and long plate structure they tended to be more prone to physical microphonics in guitar amps but when you found a great one it was really something.

Plate current in this tube?  All over the map and some of these tubes would run very hot for a 12AX7.

The tube was not any more linear than a Sovtek 12AX7LP or LPS.  The New Sensor Mullard Reissue was in the same ballpark.  The LP/LPS was more consistent.  

The JJ 803S has more linear traces, takes longer to compress and has a similar rise time.  It is a more consistent tube.  Sonically you would have to make your own call.  The JJ 803S is about $14.95.  Again, make your own call.  There is also a $24.95 JJ 803S gold pin version that tested the same as the version that was $10 less.  For some strange reason they test the same.

From the same company that brings us this B759 there are a few more offerings.  The Mullard reissue that some may think bears some resemblance physically to this tube (I would not begin to imply that I understand the magic that makes these tubes different that I miss in my own inspection and testing) sells for about $16.95.  The Sovtek LP / LPS sell for about $12.95.

A typical 12AX7 data sheet can be found here.
http://www.guitaramplifierblueprinting.com/files/GE-12AX7.pdf
Keep in mind than many folks who make tubes copy some of the data off these sheets and put the specs into their own data sheets.  They don't make tubes that come close.

In the past during the six plus years I was at Groove Tubes, their CEO Aspen Pittman let me publish my test results and send the results to the tube makers.  We also produced data sheets based on measured results rather than on hopes and wishes for all the major manufacturers.  Data was also part of the hard copy deluxe edition of The Tube Amp Book.  JJ was the only manufacturer at the time (2002-2008) that would act upon what was reported and make changes.  They also kept in touch and followed up.  New Sensor / Sovtek could care less.  If somebody sends a copy of this to them I would be more than happy to explain how everything was done and give them all my test procedures.  Based on past experience I don't think I have to wait by the phone.

As a side note, Aspen Pittman made countless trips to the factories that were producing his "NVM" tubes and I had monthly meetings at the GT factory on the GT exclusive tube line.  Aspen went through hell on the 12AX7M and 6CA7 trying to make them right.  The first three runs of the 12AX7M were the best 12AX7 tubes I had ever tested.  Unfortunately the factory could not keep up the quality or consistency.  

Conclusion on this B759 screened tube:  Pretty box?


DATE TUBE B+ volts BIAS volts mA actual TC (gm) actual gp Plate Resist Gain Comments




1.2 1600













3/23/2013 Genalex Gold Lion 250 2 1.6 2420 0.0285 35.1 84.91 A Sovtek 12AX7LPS by another name

B759 Reissue

0.8 1190 0.0180 55.6 66.11 A “Mullard” reissue by Sovtek by another

$44.95 each

1.0 1430 0.0190 52.6 75.26 name.




1.2 1550 0.0170 58.8 91.18 This is the one tube that came close




1.1 1460 0.0170 58.8 85.88




0.9 1610 0.0190 52.6 84.74




2.1 1640 0.0210 47.6 78.10




1.1 1550 0.0190 52.6 81.58




1.0 1560 0.0180 55.6 86.67




0.8 1320 0.0160 62.5 82.50














Output TC
Plate Res Gain

Averages

1.2 1573
53.2 81.69 <- Output averages




96.7% 98.3%

81.7% <- % of standard spec





















High TC

2420 151.25%


12AX7 Design Spec

Low TC

1190 74.38%


1.2mA current output

QA tolerance TC

76.9%



1600 TC









100 gain

High mA %

2.1 175.0%


62.5K plate resistance

Low mA %

0.8 66.67%




QA tolerance mA

108.3%















High gain

91.18 91.18%




Low gain

66.11 66.11%




QA tolerance gain

25.1%




2 comments:

  1. Gold pins make the electrons feel better about themselves. When they do, they don't sound as whiny and sound happy.

    ReplyDelete
  2. Myles, great job! Nothing better than seeing current production tubes tested. Not too long ago (ok, almost a decade ago) JJ's ECC83S was the top dog.

    It would be nice someday to have a new production real 12AX7 that meets minimum spec. I won't hold my breath.

    ReplyDelete