My Audio Note Kit One SET Amp DIY Journal

Updated: November 11, 2005
Rev. 1.2c -- Adding more NOS, used tubes testing results (6SN7 and 5687).
Rev. 1.2d -- Adding few more 6SN7 tubes.
Rev. 1.2e -- Adding RCA Redbase 5692 tube & CBS JAN 5692 tubes.

(Project started December 2004 and completed in Feb. 2005!)

Notes: Click the picture with a frame to view in bigger size. 

Project Goal and Concept
The Single-Ended (SE) 300B power amplifier has, somehow, became popular again and gaining very good reputation since 1990s.  In my times (attended college in the 70's), vacuum tubes radio and TVs was part of our lives, but was never a major part of my college curriculums!   In my mind, vacuum tubes was thing of the past and it is long gone and will never return to real world again!  Those who are interested in tube audios are, to me (no offensive, but..), some older guys who lives in the past, with some wonderful memories!  Many years ago, before I really get into the DIY, the brand like SONY, Panasonic, etc., are to me the best audio I can have!  Boy, was I wrong then!  Making Solid-state amp of Nelson Pass' design of Aleph 5 and another version of design based on his patterns, the Aleph X, totally change my view about "good" music.

In 2004, I heard about the story of 300B tubes and how good the music it has.  Originally, I was not that interested, because the tube amp's high-voltage really scared me off!  (I only have one life!).  Secondly, the never ending types and numbers of all kind of tubes really confused me!  What convinced me is when I read an article of a music lover who talked about his journey and how he ended up in finding the ultimate sound from his Audio Note Kit 1 300B SE power amp.  One of his friend, a long time music lover and DIYer, after listening to his amp was not able to sleep due to the music he listened on that AN 300B amp.   For this reason, I have decided to try to make a SET amp for myself. 

In the beginning, I did not pick Audio Note Kit One to try first.  From the study of tube amp, I made (or should I say, learn from a good DIYer) a simple list of what would be a best tube amp that gives good sound:

  • Single ended
  • Pure Class A 
  • Direct Heated tube (triode)
  • don't use negative feedback
  • mono is better than stereo
  • use tube rectifier
  • use as minimum parts as you can (simple is the best!)
  • Don't use parallel design

After some search, I decided to make an Audio Note Kit One from the kit provided by Audio Note (it is a stereo one, not mono).  Thought it is not cheap, but it is a good start!  I hope to learn more along the way!  The other reason I choose it is I prefer DC filament supply than AC.  My previous 2A3 is AC filament powered and I hate to deal with the AC hum!  Though I am having fun doing DIY, my main goal is the good music to enjoy day-by-day.  As long as I found a good amp, I will stick with it!

 

 
Project preparation
(I have made the same preparation comments on my 2A3 SE amp.  If you have seen them, then, I don't try to bore you again.  If you haven't seen it yet, you can click the "Show Content" to view it.)
   
To make a DIY successful, fun and able to do some debug if anything did not goes well, this is what I think a DIY should do:
  1. Pick up the basic Electric/Electronic book to get familiar with the knowledge you need!  This not only can "save" your life, but also are a better fun if you know what you are doing!
  2. Carefully study the manual and/or other DIYer's journal.
  3. Study the schematic as long as you can until you know which part is doing what.  Write down each middle points where you can measure if when doing checkup or debug.  Even though there are many DIY sharing web site and newsgroup, I found out 90% of the problem I resolved it are from my own study of the schematic and compare it with my work!
The official link to the Audio Note Kit 1 are at: http://www.audionotekits.com/   You can find the basic information there.

I ordered the new Audio Note Kit one (with new non-magnetic stainless steel chassis) in December, 2004.  Brian Smith of AN Kits are kind enough to offer me with the new hard wired board for me to test.  With a good design, it saves me from have to calculate the working point, which is a lot of work!  The standard kit came with the Group B transformers (power x 1, 2 output transformer and one PSU choke).  According to many diyer, Group B has the highest C/P value!  

I have compiled a preliminary Parts List here.  Use it as your reference only.

Design Schematic
The schematics for the Audio Note Kit one are:

or you can see a different version here:

This is another version of modified AN Kit 1 I found (a DIY group project):
Some Info before beginning (if you are doing from scratch)
  • 300B tube's filament can be powered by AC, regulated DC or Passive DC 5V.  All have their own religious believer which is the best!  Just watch out, if you are using the DC, on the 300B tube's min and max filament currents.  Carefully pick the right regulator IC.  Standard 7805 takes 1.5A, while 78S05 can take upto 2A.
  • Some 300B NOS has problem of reliability (burned out after couple hunderd hours).  Carefully ask the question of manufacturer and batch before buying NOS tubes, unless you have deep pocket!
  • 300B tube's filament is direct heated cathode wires and are brittle when it is hot and easy to break at this time.  Always wait until it is cold to handle it!
  • I was told, from review, that average burn-in times is about 200 to 300 hours to get the true performance of 300B.  Patience is the virtue as always!
Power Supply
  • AN Kit 1's PSU are in one PCB that use RCL filter to provide the High Tension DC voltage for the driver board.  Watch out for the part that deals with the 435V power.  Take great caution in handling them.  Make sure all part are secure and insulated well!
  • 5U4G rectifier tube are provided by the 5V AC from the power transformer.
  • 6SN7 and 5687 tubes are provided by the 6.3V AC, center-tab, from the power transformer.
  • Filament is using a Filament PSU board using a silicone bridge rectifier and a regulator IC.  If you are doing DIY yourself, be sure to choose the 78S05 regulator IC.  (standard 7805 takes less current than 78S05).  The key point here is to use Mica Insulator and an insulated screw washerfor the IC when bolt it.  Remember to bolt the IC not too tight, but not too loose either!  Put a Thermal Paste on the back of Mica.
  • Remember to twist all the power lines to prevent noise induction to the signal path!
  • If possible, use EMI Ferrite filter to all the power lines to filter the residual EMI.
 
Putting all together
Making the AN Kit 1 isn't that difficult!   Careful planning or following the manual will make it even more easier!  AN Kit 1 is not a point-to-point connection.  The 3 PCBs (PSU, filament supply ad main board) make the installation easy to do.  

To make my life easier and make it successful first, I decided just to follow the manual and do no change at this time.  I will leave some rooms for my future upgrade or modifications.

 

I changed the speaker binding post to a better one.  I preferred the binding post to be in-line for better connection of my heavy speaker cables.  Luckily, Brian (of AN) told me that they have a new case that just have this change.

I also was planning to add additional set of RCA and a toggle switch to switch between two sources I used.  I finally gave up, because the AN stainless steel is too difficult for me to do hand drill!

 

This is my initial planning and work.  Carefully identify the color of the wires is very important!

Remember to twist all the wires, especially the power wires!  This will reduce the induced noise into the signal output lines!

Two small problems I have encountered during installation.  The PSU resistors on the bottom side of the PSU is touching the chassis (not shown!).  I have to add additional plastic spacer to move the board up a little bit for the extra gap!

The other is shown at left that the upgraded TKD pot's lugs came in touch to the AN Oil Paper cap.  As a result, I have to remove the cap and add extra length (use OFC copper wire) to both cap's leg and move away from the pot!


This is the initial testing after my installation.  The sound is really pleasing and tight focus with good image.  Better than my first 2A3 amp! 

The finished amp is quite heavy!  I take great precaution to protect my back when moving them around!

I use the following steps to make sure all are working, before pop-in the expensive 300B tube.
  1. For safety of your 300B tube, don't use the fuse higher than needed.  AN Kit came with a 2A slo-blow, which is a good protection for the amp.  Don't change this fuse, or your will be sorry!  (If the fuse did not hold, there is something wrong with the installation, not the circuit design.  In my case, my tag board was broker and I replaced it w/ Radio Shack one.  This piece is center bolted on the case.  I accidentally soldered the center tag with my resisters on both side of 300B socket and accidentally caused a short-circuit.  As a result, it keep blowing my fuse.  I thought the fuse is too small and switch to a 3.2A fuse.  Do you know what happened?  I almost blow my 300B tube and at the end, I have two dead 5U4G bodies!  I then find out the problem on my resistors and the tag board.)
  2. Double check all the wires to make sure none are with bare wires.  Add shrink-wrapped tube to all the connected wire section, especially on the high voltage wires!
  3. With no tube installed, first make sure the transformer gives out the correct ACs (all measured against GND).  They may not be precise, but as long as in the range should be OK.
    • To Pin 4 or Pin 6 of 5U4G socket should be 425V AC.
    • Two filament PCB output should be 5V DC.
    • Pin 7 and 8 of 6SN7 socket should be 6.3V AC.  Pin 4 and 5 of 5687 socket should be the same AC.
  4. Now turn off the power and install 5U4G rectifier tube.  After power on, it should stays on without a problem.
  5. (power off) Now install the 6SN7 tube.  Power on and check to make sure it will stay on.
  6. Do the same for 5687 tubes and they should stay on.
  7. In each of the step, if anything goes wrong, the fuse should be the first to go.  If anything happens, don't drop in your 300B tube.  Check the circuit thoroughly to make sure it is correctly installed!
  8. If all looks fine, you can try to installed the 300B tube.  Installed it carefully.
  9. Now turn the power on and monitor the few things.  I put my other hand on the switch while doing so.
    • The 300B filament should gradually glows.  It should become steady then.  If it is keep glowing brighter and brighter (with outer plate is glowing red), turn off the power and check your circuit!
    • The power transformer should not be getting hotter.
  10. If all looks well.  Use a multimeter and switch to DC.  Measure the DC offset from the binding post.  They should be low (around 2~5 mv or lower).
  11. You are now ready to hook up your source and speaker for a test now!  Enjoy!
AN Kit One 300B's Musical Expressions (Conclusion)
(Disclaimer:  This musical impression only reflects my personal viewpoint, nothing more, nothing less!)

My AN Kit 1 does not have audible hum or buzz sound!  Wonderful!

With the impression I have with 2A3, I can imaging 300B SE amp would be good!  From the very moment of it's first output, I know it is good.  This is basically as-is from AN with only few parts I've changed.  The sound is very beautiful!  The image is focus, tight and clear.  The small details and high notes are very good.  Midrange and Bass are good (though have some room for improvements)!  The sound stage is wide and clear.  Vocal, guitar, piano music are exceptionally good!  Very nice indeed!

How does it compared with my old amps?  (One needs a more sensitive speaker to enjoy the SET amp.  Most said 88 dB and up, I said 90 dB and up...)

  • Sansui Au-717:  My very first Integrated amp.  Very good, but no comparison at all!  I will leave it for my HT.
  • Aleph 5: My very first DIY Amp.  Nelson's design of Aleph amp are famous for their tube like sound.  The high tune is good, but the 300B is more crispier, more focus and yet not irritate one's hear!  300B amp is easily beat A-5's in mid-rang and bass.  The drum beats, for example, you can actually you can feel 300B give more "Q" feeling than A-5.  More depth and vibrations!
  • Aleph X: my 60W "Heavy" baby (abt 70+ lbs).  Very good high and mid-range tune.  Tighter and wider stage than my Aleph 5.  Due to my case's limitation, I can only crank it up to 60W.  I believe if I can have it to 100W, it can be better!  I have two mono (Aleph 2 like) case ready, but I am not sure if my old house's wire can take it or not!  I am still debating to make it or simply use my new SET amp.  Simplicity is my new aim now!  For the music impression, my 300B has more vivid vocal feelings.  I can actually fell the breathe from the signer exhale while she sang!  Bass is better and the sound image is more clear and more separate.  One of the vocal song I have has the multiple wind chimes and you can feel the sound is clear chiming from my left to right!  With A-X, it is less of that kind of left to right, 3-Dimentional feeling. The sound stage is wider than Aleph X.  The total impression is that Aleph X is closer to my 300B than Aleph 5, but still with a gap one can feel from the speaker!  One good thing about A-5 or A-X in winter is that they provide good heater source! 
  • 2A3 SE Amp: My very first tube amp.  It gave me the confidence and desire to make my 300B SET amp.  My 2A3 have a slightly AC hum noise (I adjusted it later down to 1.2mv before comparing further) and yet my 300B is dead silence!  Of course 2A3 has less power, but with the same volume level and the same speaker, 300B is slightly better.  More warmth, bigger sound stage, though the difference is subtle!  The beauty of my little 2A3 is that it only costs me less than 1/2 of 300B!

There one tiny difference of my testing.  For AN Kit 1, I am using it with a CD direct in without a pre-amp.  For Aleph 5 and Aleph X, I am using the famous Aleph-P 1.7 pre-amp, because I did not have the un-balanced in for Aleph X!

In general, Aleph 5 or Aleph X are very close to the AN Kit One 300B tube amp.  300B, as a whole, tends to be more warmth and with roundness, but with crisp and precise image.  The sound stage is wider and more of 3-D hall feelings, like I sitting closer to the stage while the sound surround the music hall is clearly heard!  On the other hand, Aleph 5 and Aleph X are more affordable and give very good music!  (my Aleph 5 is 1/3 and Aleph X is about 1/2 the cost of my AN Kit 1, but they both need a pre-amp).  The most costly parts in this 300B amp are the 300B tubes and the transformers (and they are just the standard version).  All other parts are relative easy to get and in reasonable price and, in fact, tube amp sometimes use less parts!

 

Softwares I played for testing

For vocal, I picked one of the best among the Chinese signers in Taiwan & China -- Tsai Chin.  Her pure, colorful songs (without modern technical assisting) make her CD a good test for testing my tube amps.  This is the most used CD to test my 300B amp.

One of the Tube amp "must have" reference CD by TACET (number 074, Tube Only).  This recording is done by all and pure Tube Recording equipments.  From the very moment of first music came out, you will feel the warmth of the illuminated tubes!

This is another "All Tube Only" recording CD for Tube amp (number 117, The Tube Only Violin).  I use this CD to test my amp's high and mid-tune.   I also use this CD to test between Solid-State and Tube amp.  Not only that, the first 2 violin solos are, in my view, a very good test of your tube's performance, too!  A not so good 6SN7 or 5687 tube will make the solo very irritated to your ear....

This is George Winston's piano solos: December.   From the point of relaxing music, this isn't the one, but the piano solos is very good to examine your amp with the crispy notes from the keyboards before you!  
Some Tube Reviews
 One good thing about Tube Amp is that we can swap with different tube and get a, sometimes dramatically, different sound.  There are quite a few different reviews there, but I found out the best way is to pick your own and pick the best one that suits you.  Sound of music is very subjective to one's ear only!
Upgrade/Modification Options
  • There are many upgraded parts and paths one can choose according to AN's suggestion.  Here is the link of the reference.  I suggest the very first and a must upgrade is to replace the VR to the TKD Volume Pot.  
  • Another good AN Kit upgrade -- change to use fixed bias by RUPERT ROBERTSON.
  • Modification done by Eddie van Veldhuizen.
  • This is the drastic modification of the original AN Kit 1.  Actually it is already a new amp!

As I am a practical diyer with only a limited budget to spend, I would only do what's make sense to fit my environments (meaning 300B amp coping with my other equipments).  For this reason, my upgrade will only be focusing on the signal path.  In my mind are like this:

  • Good volume pot (Done!  I already upgraded to TKD one.  I think this is the bare minimum upgrade anyone should do!)
  • Change the RCA and Binding post (I changed to the one similar to the WBT type.  Done!)
  • Change the driver board part into Hard wiring (or Point-to-point).  I believe pure copper, 6N or 7N solid OFC wire is good enough (for me)!
  • Flexible signal path interconnections I will use the silver-plated OFC wire.  Pure silver wire is better, if one can afford it!
  • Change the Jensen/AN Aluminum Foil caps to the Pure Copper caps.  I need to save a lot for this.
  • Resistor change to, at least, the HOLCO 1W (H4P) resistors.  Tantalum resistor is too expensive for me!
  • Change the Electrolytic caps to better one.  I am using Nichicon Muse KZ caps now for the one on the driver boards.  The two caps used on the 300B socket area is already Elna Cerafine caps provided by AN.  It is very good already.  I am not sure if I would still like to change to Black Gate one.?  (Black Gate is out of production now.  Many said one should stock it first, in case we can not get it when one is ready to upgrade it!)
  • About transformer upgrade, I don't know much about them!  I will avoid spending money before I do some study!
My Equipments & Tubes
My equipments are all second hand purchase, but they are in very good condition.  Some how serious music lover always keep their equipment in good order and condition!  (Parents, be aware!  If you have a trouble kid, do an Aleph DIY with them.  The music will change them! :D)

Speaker: Triangle Celius 202 (Class A, 3 ways, 92 dB)
Preamp: Aleph P 1.7 (but now I use Direct Input from AN K1 most of the time!)
CD Player: Sony DVP-NC650V or Denon DVD-2200
FM Stereo Tuner: Sansui TU-717
DAC: MSB DAC II with upsampling or my DIY version DAC 3.0

The following are the tubes I used.  I do have a pretty sensitive ear for high and low tunes.  These are just my personal feeling toward the tubes I used.

  • 5U4G: I have tried EH and Sovtek one so far.  I like EH 5U4G tube better, because it is a GB version (275 mA vs. G's 225 mA).  I also found that the best of rectifier tube are the NOS tubes.  I have two Sylvania 5U4G and they are superb!
  • 6SN7: 

    My 6SN7 tubes Collection:  Generally, 6SN7 tube are very good tube.  To try to find out which one is the best for my 300B amp, I spent a while to collect all these good 6SN7 tubes for my reference, and thinking to find the best tube I like without fancy parts upgrade.  

    I have tried the one shipped w/ AN (don't have brand name), Philips 6SN7WGTA NOS, Shuguang 6SN7 GTB metal base and Channel Master GTB tube.  Initially, I was not able to really hear the difference of each tube, but gradually, after switching tubes back and forth, I am now able to hear some differences.  Many said the Premium red base 5692 (by RCA) is the best to get, but it cost a lot!  I am now finally able to buy one NOS to try out!   The following is the shootout list for the tubes I have (and only reflects my personal view and not yet included other few tubes that are on the way to me).  

    What to do when you have too many tubes?  Well, make a "tube box"!  It is better than sitting on the table....

    All these tube's difference is subtle!  This is the shootout list I like, so far (again, this is only my personal preference):

    • RCA 6SN7GTC NOS:  This is actually a rare metal, carbonized envelope made by RCA in Brazil (some mark as 6SN7M).  The sound is wonderfully sweet and very good bass!  Simply wonderful!
    • Hytron 5692 black base: Ah!  Very outstanding sounds!  Very warm, full with air and good details.  I compare this tubes with RCA Redbase 5692 and RCA 6SN7GTC for a long, long time.  Hytron 5692 stands out, a tiny bit edge, on all rounds.  I believe it is because it is a NOS tube; otherwise, the result may be different!
    • RCA Redbase 5692: This is a hot tube.  It took me a while to get one (within my price range).  Even though I got this as used tube, but this tube is really good that match it's fame!  Smooth, warm and airy!  I would think a NOS is definitely better!  Does it worth it?  Well, it depends.  This is almost the highest price I paid for this used tube, but it is not the best one and a few (with very little cost) are actually close to its performance!  However, if you can get it with good price, it is a tube you won't regret to have!
    • CBS JAN CHS brown base 5692:  I purchased two of this tube.  All are brown base tube, but one with red printing and one with darker brown printing.  All are in good shape and the construction suggested tat it is either made by RCA or licensed from it.  For the sound impression, one is as good as the RCA one, one is a less sweeter, apparently used longer than the other one.  Nevertheless, they are still very good tubes. 
    • Raytheon military 6SN7WGT: Very outstanding sounds!  Warm and airy!  Very close to the Hytron 5692.
    • Sylvania 6SNGTB NOS: I have many Sylvania 6SN7 tube, but this one has different construction than others.  It has a side getter like the one in GE.  It is very musical.  Almost as one of the best I have!
    • GE 6SN7 GTB: This NOS tube is a medium envelope and made in Canada.  It is surprisingly musical with good bass!
    • KEN-RAD JAN 6SN7GT: military VT-231 version and excel in vocal, a little bit weaker in bass than the previous two!
    • Raytheon JAN-CRP 6SN7 GTB: This is a military VT-231 version.  I hear a little bit more clearer in minor background instruments in this tube, but a little bit less airy than the first two!
    • Philips 6SN7WGTA NOS -- mine is made in 85'.  A very musical one.
    • Sylvania 6SN7GTB -- I purchased two types from ebay as used.  They have different looks (ver. 1 & ver. 2).  It is physically identical with the Philips 6SN7WGTA from what I can see.  
    • RCA carbonized envelope GTB: Very good sound.  I bought it very cheap and the sound is wonderful!
    • Shuguang 6SN7 GTB metal base (new tube) -- some said [6SN7] Chinese tube is junk!  Well, from the outlook, the quality isn't very impressive!  The silkscreen printing is mis-spelled and the metal base is already a little bit tiny rusty!  The internal wiring isn't that professional done, compare to others.  However, it is quite surprisingly musical at the price I pay!  This tube doesn't sound like junk at all to me!
    • National 5692 (Russian) tube: This is Russian made 5692.  Structure is similar to the Shuguang tube, but with plastic base.  The sound is not as close to my Hytron 5692 and not warm enough to my taste!
    • Channel Master 6SN7 GTB (Japan NOS) -- a little bit flat, compressed and a little layback overall!

    The other NOS/used tubes I still would like to try, but not currently owned are:

    • Tung-Sol round-plate tube (they said this sounds beautifully, but is very hard to get!)

From my testing of so many 6SN7 tubes, my conclusion of a finding a good 6SN7 is try to find a good N.O.S tube.  I found out the most beautiful tubes I have are from a careful screening NOS tube.  For the same type of tube, a NOS tube is better than a used tube in my ear!  If you can find the glass envelope is carbonized, that is even better!  Some of the NOS tubes I bought are not only very good, but also are much cheaper than the modern tubes I have purchased earlier!

Other 6SN7 references are:

  • 5687: I have Philips JAN 5687WB (came w/ AN) and Raytheon JAN 5687 black-plate NOS tube.  Again, I can seems to hear the difference!   One diyer told me if I tried the Bendix Tungsten pin NOS 6900, I would never go back to the other tube, but it really is too expensive for me (and actually another diyer told it really isn't that worthy for the price one pays!  I just buy the one I can afford and enjoy best!)  Other NOS available are:
  • 300B: I have the AN 300B tube (Chinese tube, Valve Art 98B?) and the Shuguang mesh plate gold-plated 300B-98C.  I like the Shuguang 98C better for it's better details and better high notes!  300B tube are expensive!  I don't know if I ever will get the chance to hear the WE 300B?  I guess I will be shaking if I hold them in my hand!  Naah... that would be too much stress for me....  I made this amp is to relax in music, not killing my cells!  I will enjoy whatever I have so far...  but I would certainly like to try the TJ/Full Music Mesh Plate 300B tube!  You can see some of the reviews of this tube above.  One of the particular interesting about why WE 300B tube is so good were mentioned in HK's audiophile magazine (as link mentioned above).  It said the WE 300B has 10 special characteristics to claim not only as the king of the valve, but also worth every penny of it!  
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Credits
  • Brian Smith of Audio Note provides great helps!  Very good parts package and good manual.
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