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)

Wednesday, May 8, 2013

Current Production 12AX7 Tubes

Click on this image for a larger image

I have been promising a current test of some of the current production 12AX7 / ECC83 offerings and have just completed my testing.

Gain and Transconductance. Some folks confuse these two things. Maybe this will help explain:

Gain is the factor by which an amplifier multiplies a signal. It is the product of the output voltage at the plate divided by the input voltage at the control grid. Gain is a unit-less factor since both measured signals are voltages. (voltage)

Transconductance is a measurement of the ability of a tube to transmit current. It is the product of the output current in amps divided by the input voltage at the control grid. Transconductance is significant in that it shows us the difference in current capability that is generated by variations in plate impedance between tubes. (Current)

When I test tubes I also measure standing plate emissions current for preamp tubes that will be used in the phase inverter position. Plate current is one factor that many tube testers do not measure.


150 tubes were tested. 15 of each type.  The above lines on each tube are the average of that particular tube.

Click on "read more" to continue.


QA rate:

A moderate reject rate means that the QA variance was more than a 50% spread from low to high factors in either plate current, TC or gain.  High reject rate means this was over 75%.  I have not found any LOW reject rate tubes ( less than 50% ) or UL /  Ultra Low <20% at this point in any current production tube I have measured since the turn of the century (2000).  Finding UL rate tubes is common in NOS offerings from Raytheon and RCA Command Series to mention just two out of dozens.  This was common in the past.

If you look at the hard cover Tube Amp Book from Groove Tubes you will find pieces by me.  There are also QA numbers on some current production tubes that are quite good.  There are two reasons for this.  One reason was that only one factor of four (plate resistance, plate current, true gain, mutual conductance / transconductance) was used in some cases.  The other reason is that some tubes tested were GT Gold Series which were already tested for some factors.  I look at all these factors currently and publish the WORST number of the four factors.  If any one factor is off the tube is not right.  If plate resistance is off there will be all sorts of issues that range across sonic, life, heat, reliability, crosstalk across triode sides, low gain, high plate current and high heat and more.

These tubes come from the same places that most amp builders procure their tubes from.  They are NOT from any of my favorite vendors who test and grade tubes.  These are supposedly tested by the manufacturer which is sometimes doubtful based on my observations.

I have the tubes shipped to friends in various spots in the USA and then sent to me so the vendor does not know they are for me.  I do not want cherry picked items, I want what amp makers receive.  There are a high percentage of tubes which are microphonic.  Some vendors will let you ship them back for replacement.  Some will not.

When I was at GT for a half a dozen years they had a no questions asked 180 day warranty on preamp tubes.  That was pretty cool.  Their reject rate before they were put in stock was generally 50% or higher.  They did do very good testing on preamp tubes (Gold Line ... Silver series were a different story).  On Ei long smooth plate the reject rate at GT was commonly 90%.  GT eventually stopped even trying to offer these.

What I learned from these tests is as follows:

1.  Know and trust your tube vendor.  Tubes procurement is a crap shoot at best and the odds are far better in Vegas.

2.  There are more models and variants of tubes made today than there were five years ago.  The quality is worse.

3.  There are multiple versions of the same tube with either different names, a slight cosmetic change such as shape of the getter, gold pins, etc.  Gold pin tubes had a higher cost but were generally more close in tolerance to spec.  Not good for the most part, just not as bad.

4.  Know and trust your vendor.

5.  My heart goes out to amp repair folks and amp manufacturers.  It is difficult to find good tubes for one amp.  Finding enough for production must be virtually impossible at times.

6.  Know and trust your vendor.

7.  The most consistent tubes AND most close to design spec were Ruby Tubes Chinese 12AX7C tubes.  I am not too surprised as Tom McNeil works very closely with the Shuguang factory and his testing parameters are held to closer tolerances it seems.

8.  Tubes that could be abused the most, vibrated, run at over voltage; Sovtek 12AX7WA and JJ ECC83S.  Both short plate designs.  The 12AX7WA is the workhorse of the industry as it is cheap and the low gain makes it more forgiving in noisy designs.

9.  Know and trust your vendor

10... and lastly .... know and trust your vendor.

Two vendors I use and trust, and have for years:

www.kcanostubes.com
www.dougstubes.com

Click on the image for a larger presentation



I just added the above to include the Tung Sol Reissues from New Sensor.  These tubes are VERY similar to the EH and EH Gold pin.  The item in the list is called the ECC803S.  It has gold pins.  It may be more highly selected than their non gold pin version.  The mica supports for the internal structure are star micas which may or may not lead to less microphonics than the less pricy version which sells for around $15 retail as opposed to about twice that price for the ECC803S version.

5/9/13 Added two more popular 12AX7s to the report. If you have a request on a common production 12AX7 you wish to be tested please let me know.

I also have many power tube tests published in the past. Power tubes are a bit pricy to test as you need at least a dozen of each from the same run so these tests are not done as often. 

I will update this post with new data as it is available.

5/10/13

I mostly use JJ's but sino-chinese are good for high gain apps. got any info on the sino tubes?

Below is my response to the question.

Sino is not really a company.  It is a conglomerate of smaller tube companies in China.  Their offerings are very inconsistent.  Chinese is really Shuguang for the most part for the most reliable and consistent Chinese offering.  Even then they can be short lived and inconsistent unless the contractor who uses them as their OEM is on top of them every minute.  When I was at GT I had face to face meetings with them every month for years.  The 6L6GE was a great tube.  The 12AX7M started out as the greatest 12AX7 maybe ever made and turned into the worst nightmare and most inconsistent and unreliable tube ever made.  Their 6L6 tubes are generally of very old design that was cheap to produce then and very poor now.  They are generally rebranded as "PM" tubes and some other bargain brands.  They have a very short life and are very weak.

Did I even answer the question here?  Probably not.  The answer really is there are no specific Sino tubes.  What you buy today is not the same tube as you will buy tomorrow.

Hmmm... I think I will copy and past this into my blog piece for others that wonder why I don't test Sino tubes.

Where do tubes actually come from?  Here is a link to a piece on my GAB website that is a bit old and may be a bit out of date but there is some good info in there if for nothing more than for history:
http://www.guitaramplifierblueprinting.com/tube_makers.html

5/21/13 Update

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Adding the link to an earlier "Genalex God Lion" report.  This was the previous batch.  Very inconsistent:
http://la-economy.blogspot.com/2013/03/genalex-gold-lion-12ax7-ecc83.html

5/22/13 Update - Phase Inverter tip.


  • Ross Fletcher Thanks Myles! How typical is this with old tubes? would phase inverter tubes wear out quicker in these amps?
  • Myles Rose Phase inverters are the hardest working preamp tube in an amp. 6L6 amps with a quad should have the PI checked when output tubes are replaced.  EL84 duet amps can have a PI last for years.
    10 hours ago via mobile · Like · 1



Phase Inverter tip:

If your tube vendor can measure plate current this is what should be done for tubes for PI use rather than use mU or transconductance measurements. It is current, not gain, that provides the drive for your output tubes.

In the case of a 12AX7 the proper spec is 1.2mA. Too many tubes today fall far below at 0.7-0.9. Low plate current will make the amp loose, flubby, indistinct. They will also distort earlier and pass this right to your output tubes giving you less headroom than the amp was designed to provide.

If a 12AX7 has too high of plate current, above 1.4mA, this is also bad. It indicates that the plate resistance is too low and the tube was not made properly. It is a reject. In this case the plate current is high because of improper plate resistance. The tube will not have the proper gain and will run hot.

10mA is the spec for a 12AT7 as a side note.


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The Canadian Northern Electric 12AX7 has just finished it's testing and the results are very good.  This may be the best 12AX7 currently on the market.

These tubes sell for $57.95 in 1-4 quantity, a bit less for 5+  They are sold by www.thetubestore.com and perhaps by others.

From The Tubestore website:

Northern Electric had a rich history of producing high quality audio products and vacuum tubes in Canada. We are now re-introducing this classic brand and bringing to you the highest quality tubes possible. 

The Northern Electric 12AX7 is made with the highest quality materials. From the glass bottle to the gold plated pins, everything is designed to give you unsurpassed audio quality. This tube has very large smooth plates. This design is much like a Telefunken 12AX7 / ECC83 smooth plate but a bit shorter. This design provides plenty of gain while maintaining an extremely low noise floor. It has been torture tested in a JTM 45, a Deluxe Reverb, an Orange 50 watt combo, and Bandmaster Reverb, with no failures or noise problems after hundreds of hours in clubs and studios. It doesn’t matter if you use an American or British design, this tube works. 

In our listening tests it was easy to hear that the tube did not change the voice of the amplifier as some preamp tubes do. The Northern Electric enhances the sound across the entire spectrum. Our testers have reported no noticeable spikes or weakness in the lows, mids, or high end. The highs are very smooth with a balanced midrange response and warm, full bottom end.

My own findings:

These rival NOS tubes in every regard.  How long they last will be told as time passes but even running them at 350 volts B+ and at 150% rated current output the life cycle was just as good as most NOS tubes from the 60s and better than the JAN tubes from 1988 or beyond.

The QA variance was 34% which is at least half that of other current production tube averages and 1/4 of some of them.  Smaller numbers are better.  The range of max recorded spec to min recorded spec are a ratio of each other.  65% is pretty good these days.  150% and more is not uncommon.  At 34% these are pretty darn nice.  If you look at the GT hard cover Tube Amp Book you can see some of these QA variance numbers on tubes I measured in the past. The main factor I use for QA/QC variance is plate resistance.  If this is off something or everything will be off as well.  Holding 62.5k spec on plate resistance is where folks go wrong.  The Tung Sol ECC803S gold pin tested on 5/9/13 had proper plate resistance but it was not as consistent as this Northern Electric offering,  The Tung Sol tube also was more noisy and compressed more quickly.  It was also not as smooth or linear.

In the end the sonic and tone qualities are user preference but this is a very nice tube from a design and quality standpoint.  I will keep looking at these as different batches are available in the future to see if this is a repeat story of the GT 12AX7M which started out amazing and over four years turned into the worst 12AX7 ever produced.

6/13/13 - A bit of dialogue and my reply on Z-Talk

From markT

From the Tube Store website: "Northern Electric had a rich history of producing high quality audio products and vacuum tubes in Canada. The original owners, Bell Canada and Western Electric, formed this company to produce telephone and audio equipment including vacuum tubes. Western Electric licensed their designs, processes, and technology to Northern Electric for the first fifty years of their production.

We are now re-introducing this classic brand and bringing to you the highest quality audio tubes possible. We are working together with a small, foreign tube manufacturer to produce exceptional high quality versions of common audio tubes. And while this manufacturer is not well known, they are the “Ferrari” of tube manufacturing and design.

The manufacturer’s immaculately clean factory houses state of the art and high precision equipment. All of the design and production is overseen by a living legend in tube design, Zhe Shen Liu.

Upon arrival in Canada, each tube is rigorously tested in a three-stage process for noise and electrical functionality. Tubes passing this are then printed and packaged for sale with an extended 6-month warranty.

We are excited and pleased to present our new reissue Northern Electric audio tubes."

So am I reading this correct Myles, Made in China, shipped from Canada?

http://ztalk.proboards.com/thread/57056/northern-electric-12ax7-tube-results#ixzz2W78QyVJb

My reply:

Mark,

If that is what their data says I will not question it.

The issue I have with Chinese tubes built under a specific contract is that the initial runs are fantastic as the maker goes out of their way to meet promises and establish the brand. As time goes on things decline. In my own experience it is not an up and down path but more of a down path. In the case of the GT12AX7M the path went from the best 12AX7 ever made to the worst ever made in a span of about four years over a dozen or so production runs.

At the moment the tube is a winner but will this remain the case? Only time will tell. The Chinese can make some great products but their consistency is not good at all. I would not be surprised if the formula on the materials change to maximize their profit (the factory) while charging The Tube Store the same price. I would not be surprised to find the tubes tolerances drift as labor time is reduced and watch microphonics rise and specs drift. If they are shipping a lot of these the changes will come sooner than later. Perhaps the factory has finally learned that consistency is the key and when you have a good thing going to leave it alone. This seems to go against Chinese business culture but I hope I am wrong. 

As a side note I am going to copy and paste your info into the blog piece along with my reply here. We will see what happens down the road.

7/22/13


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The lower the gain the lower the noise.  Cryo treatment does not make a tube more quiet
Cryo treatment in my testing has resulted in shorter tube life for me and more brittle internals which result in
a tube being more prone to physical microphonics.

Sovtek 12AX7 Black Sable Cryo treated and graded tube.

These are sold as matched pairs at $49.95 each.

Bottom line:

Low noise was accomplished by having low gain.

These were no different than non treated Sovtek 12AX7LPS.  They were no quieter when compared to tubes of the same gain of the same LPS type.

They were no more consistent than any graded or selected tube.

These did not handle over voltage or over current any better than non treated tubes.

These are roughly twice the cost of a standard Sovtek 12AX7LPS which you can get from a good tube vendor in a nicely tested state.


The test results for these are the last entry, 7/22/2013
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I was asked about PSVane tubes by Shuguang on the Z-Talk Forum.  My reply:


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Shuguang is the largest tube manufacturer in China.  Over the last decade they made some designs under contract for various companies, the first of which was Groove Tubes from 2002-2008.  GT supplied the original engineering drawings and parts.  Shuguang learned that there is a market for "vintage" type tubes.

Over the years Shuguang would "backdoor" GT supplied and exclusive parts to some of their other customers.  One of these customers, TAD of Germany, sold the GT 6L6GE with black vented plates made from GT parts.  They were sued, successfully, and the 6L6 TAD stock was turned over to GT.  GT then sold the tubes as a Chinese 6L6 until that stock was gone.

Shuguang learned that there was a market and it was a simple matter to print up slick boxes, gold plate metal bases on some models and dramatically raise price on basically the same item in new clothes or a change of an internal design with no attention to quality, material or QA/QC.

If you look at their website under Quality Control you may ask yourself, "why don't they do this on their other tubes".  I asked myself the same sort of questions as their engineers could not explain to me how plate resistance changed and was half the spec value on the 12AX7M year after year in monthly meetings I would have with them face to face.  


They are off and running.  Charge a high enough price and there will be some great reviews.  It is human nature to want to exclaim how right, lucky, brilliant you are by trying to justify that you just spent $83.00 a pair for 12AT7 tubes that have a suggested burn in time of 75-100 hours before they are stable?  You've got to be kidding me.


As a side note, the data sheet on this tube is a flat duplicate of a 12AT7 data sheet from all tube makers from the past.  Once again people .... Just sell consumers a tube that meets spec for your standard offering.

Take a look here.  You can pay even more for the series II tube!  Or .... check out the dropdown menu and buy the tubes that are substandard, not well matched, more noisy but, although still more expensive than anything out there they come in less pricey versions.


7/23/13 Update

6/10/2013 Northern Electric 12AX7

1.3 1610 0.0165 60.6 97.58 $57.95 but they work. QA = 34% - xlnt
7/23/2013 Northern Electric 12AX7

1.0 1420 0.0158 63.3 89.87 New test. QA now 51% - moderate

Above is the update on a tube that looked very promising.  I was able to procure a new batch.  The numbers were not as impressive.  

I have read this story before.  Things start out great, demand is high so production speeds up.  Next thing you find is that it is business as usual.

7/24/13 Update:


Currently testing the TAD 7025S.  It is a $35 tube that is supposed to be a copy of the famed Mullard.  


So far things look like .... well .... TAD works with Shuguang and TAD used to steal GT parts (or Shuguang would back door them to TAD on their 6L6).  Lawsuit ensued and GT won.  



Bottom line .... these TAD 7025S tubes sure look and trace like the last and worst version of the GT 12AX7M.  Perhaps the Chinese found a way to collect some more money from old GT tooling and designs?  I will know more in a few days.

7/28/13 - TAD 7025S results added in last chart entry below.



Click on chart for larger version
Bottom line:  Very much like the old GT 12AX7M in the last production runs.  Low gain, lots of heat, inconsistent.  They would test great on a simple tube tester with their high TC due to low gain and low plate resistance which would lead some to believe they had a winner on their hands which is anything but the case. The curves are not very smooth or linear.  High percentage of curves where the two sides cross which means possible interaction of the A and B sides which some circuits may not like.  

8/29/2013

I generally test new/current production tubes but I also test tubes from friends and associates which include audiophiles and engineers.  


Last week I was brought 27 Raytheon tubes made in 1962.  These were NOS / NIB (new in box). Their condition was unknown as the boxes were unmarked.  My usual sample quantity is generally larger than 27 tubes but there were enough for a decent test run so I thought I would add the results to my ongoing tests.  


As a side note I have data compiled from 2002 and all my data from six plus years as GT Tech Support / SAG if folks want any of that info but it is too verbose to post here.  This info is not available for simple curiosity but rather for those folks active in tube development or manufacture.




Bottom line on the test results was no surprises.  The tubes all met design spec (actually all of them did better than design spec).  The tolerances for plate current, gain, mutual/transconductance, plate resistance were all tight, proper and consistent.  The curve traces were all smooth and the A and B sides of every tube were very closely matched.  In the 27 samples, 22 of them had curves that were right on top of each other meaning the tubes were matched across the entire operating range, not just a single static point.


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July 2015 Update


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March 17, 2016

Update .... or actually, not really any good news.


So far in 2016 there have been a number of "revisits" on many of these current production tubes. The bottom line ... not much to report as nothing has improved. There are some new names on the same tubes and the QA has gotten even more sloppy. That is all that can be stated at the moment.

- end -

19 comments:

  1. gotta love candid info from knowledgeable people. thanks, Myles

    ReplyDelete
  2. Excellent Myles! Thanks for confirming why over 65% of the current production tubes we buy are rejected.
    Thanks,
    Will

    ReplyDelete
  3. For an effects loop slot, what is a good choice as far as gain goes? A 5751, 12ax7, 12at7, etc.

    Cheers.

    ReplyDelete
    Replies
    1. It is a matter of personal preference but I'd use the type of type that the amp was designed for in the first place.

      Delete
  4. Kind of curious about the JJ 5751. I'm using it in a "Test Mule" tweed Princeton (5F2-A). This is home built by me with upgraded components. Any thoughts?

    Rich Merriam
    Concord, New Hampshire

    ReplyDelete
    Replies
    1. The JJ 5751 is not an actual 5751. It is little more than a 12AX7 that did not make the grade. Read my pieces on 5751's and what a real one is and used to do. They are a very different tube held to much higher standards.

      But .... if you like the tone, and have compared it to real 5751 tubes tone, then things are great ... other than reliability .... In the end it is just personal taste.

      Delete
    2. The JJ 5751 is not an actual 5751. It is little more than a 12AX7 that did not make the grade. Read my pieces on 5751's and what a real one is and used to do. They are a very different tube held to much higher standards.

      But .... if you like the tone, and have compared it to real 5751 tubes tone, then things are great ... other than reliability .... In the end it is just personal taste.

      Delete
  5. Norther Electric is made for "The Tube Store" by a Chinese manufacturer in Shenzen Province. I am fairly sure it is the Gui Guang factory which is, more or less, as family owned as you can get in China. Sino was essentially the old People's Republic of China communist military establishment collective's version of the old USSR/Warsaw Pact's OTK stamp. Some old Sino tubes also carried OTK stamps. Coke bottle 6Pi3s come to mind. Philips dumped some of their vac tube tooling in China at Shu Guang's factory(ies) after the Koreans, Indians and Japanese had used it under the Transfer Of Technology "TOT" exchange. By then a lot of it was beyond any practical use. Shu Guang makes the 12AX7B (made in several progressive & regressive versions) and the 12AX7C (again with various changes along the way). I will give them some credit for not trying to use 50-90 year old tooling to make plates, and actually "try"(?) to make things a little better (?) or at least differently. I said "some" credit, but not much. There is a video made at Shu Guang where you can see the workers washing the glass tubing in "the men's room" with tap water. EI may have made a tube that was either okay or a useless microphonic pile of steaming crap (roughly 50:50 odds on what you might get), but at least they used DI water to clean things. We got lots of EIs labeled "National Service Master" 25-35 years ago. They were pretty crappy compared to the GEs, RCAs, & West European tubes. I am 100% certain the premium price for Northern Electric 12AX7s is to pay for testing and selecting tubes that are not junk. I won't mention any names of suppliers, but they cease to become friendly after about the third batch of returns based solely upon testing. Usually I have to pay return shipping, (the word "usually" indicates one maybe two suppliers are/is close to my house) and take the time to pack & ship stuff back. Electroharmonix comes in better and worse batches with no consistency over any period of time to speak of. An actual good batch of EHX is really rare. Some of the retailers & wholesalers got funny about me sending back tubes that they deemed were "fine". . Real NOS 5751s from GE were "5 Star Tubes". They were "for applications where dependable performance under subject to shock & vibration is paramount" (RCA). There are some 12AX7s "for use in mobile equipment" that carried the four digit Mil Spec & Industrial numbers. Seeing "7025" stamped on a modern production 12AX7 tube pisses me off. There is no way they selected anything based on low noise & stamped it 7025.

    ReplyDelete
    Replies
    1. Whoever posted the above comment ....

      Thanks for the commentary. Feel free to comment anytime.

      Delete
  6. Myles,

    As always, thanks for sharing your test results!

    27 black plate Raytheon couldn't find a better home..

    -Rick

    ReplyDelete
  7. Myles,
    Thanks for publishing your findings. Question....Which Ruby 12AX7C were you testing? 12AX7AC5 or AC7? Thanks in advance for your time taken to reply to my question.
    -Shane

    ReplyDelete
    Replies
    1. Shane,

      These are the AC5. I have tested the Ruby 12AX7s for years at this point as well as many of their other tubes. Back in the early or mid 2000s a review I wrote on their EL34BSTR was published in the first page of their tube catalog. These catalogs were handed out at NAMM that year. At the time I was tech support for Groove Tubes and the GT booth at NAMM was across from the Ruby booth in direct sight. It was interesting as folks came to ask my take on Ruby when I was working at GT. Aspen Pittman always accepted that I wrote what I observed. Over the years I felt that Ruby provided great products at a very fair price and their testing and QA are top notch.

      Delete
  8. Great work, really enjoyed the read.

    If you were to recommened 1 modern production 12AX7 what would it be?

    Cheers

    ReplyDelete
    Replies
    1. Tubes are very much a matter of personal taste and preference and my thoughts would vary from amp to amp, player to player.

      In a manner of speaking, trying to answer would be as tough as me asking you .... what should I have for lunch?

      But .... for a generic, all around, wide use 12AX7 tube made at the moment (as in this month), the Tung Sol Reissue is a good bet for being close to linear, not extreme in any characteristic, more reliable than most and fairly consistent compared to most others.

      Delete
  9. Thanks for the info Myles this was a very interesting read. I do have a question though; You often mention the Groove Tubes 12AX7M tube and how it started out very good but just got worse and worse over time and subsequent batches. Is there any way for the layman to tell one batch from the next by any markings or features on the tube? Are they numbered or coded in any way?

    ReplyDelete
    Replies
    1. No codes. No design changes other than some minor ones such as crimped plates rather than spot welded but this did not change performance. If you have a TC tester and the tube reads amazingly high, as in about 2300 rather than around 1600 which is spec, it is one of the later garbage tubes.

      Delete
  10. Myles,
    First, many plaudits for running a blog that provides a genuine Benefit for Humanity. Fascinating and highly useful insights to be found here.
    I stumbled across it because I'm in the process of building an EAR834 phono stage pre-amp, largely following notes, gudance (and a link to here) from 'Spaceistheplace' who can be found, along with much else that is fine, at the Lencoheaven forum.
    I've selected Mesa Boogie SPAX7 (no idea what Mk. they are) to fill the V1 and V3 positions and NOS Sylvania 12AX7A ECC83 (7025) for the V2 slot. Do you believe that these valves will be subject to the same degree of inconsistency/uncertainty/variability that you talk about elsewhere? Also, given that I'm in the UK, how should i go about finding a vendor I can trust? Do l simply look for one who is able to test every tube they see?
    Nick

    ReplyDelete
  11. Tube selection is a personal taste issue. The tube types you have picked are fine tubes when properly tested.

    A vendor who does not test every single tube is not a viable vendor. You should get some sort of report with any, and every tube your purchase. As you can see in the test results provided here, even in the same batch there is a huge degree of variation. Just because a tube is "new" it is not even good or always a working tube at all. Many vendors cut out testing and just rely on their warranty of replacement if there is a problem. With most folks, the hassle of reboxing and shipping is not worth the effort and just toss the tube if it just a dual triode.

    There are some great vendors in the UK. These are my favorite folks on your side of the pond.

    https://www.watfordvalves.com/

    ReplyDelete