FET Audio | Hi-End Audio & Electronics DIY Electronics & Repair

Recently I bided a pair of 6DJ8 – Amperex from Germany (USD $5, see photo) ebay item number 290488910892.  This is a used tube and expect the performance is not as good as NOS.  So it ends up to be one tube with much higher noise level as shown in first 3 photos. Even the noise level is higher for one tube but I really cannot hear the difference between them.  Amperex tube sound good!!!  Thus our ears are really not able to tell much about tube variations!?

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Another experience is a lot 10 pcs of Russian 6N23P (USD $10), ebay item number 260680492416.  All of them has much higher microphonic noise than US brand tubes and 7 of them with extreme high frequency buzzing noise when knock on the tube body.  The buzzing will extended few to 10 seconds!  See last photo.  The seller has refunded me partly due to this problem and I am happy with his compensation!!!

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I use all the tubes in my Mu-Stage pre-amp!

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This is a tube pre-amp using Mu-Stage.  It use 6DJ8 + 12BY7 mu-stage and 5Z3P rectifier tubes.  I use lot of chokes inside also and good Jenson capacitors.  The casing is 100% aluminium and is self make one.

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Update Sep 22, 2010:

I have upgraded the internal capacitor using some Russian PIO capacitors like KBG-I 0.01u, K40Y-9 0.22u and MBGO 0.25u.  The sound become more transparent!  Now this preamp is a good match for the OCL PCM1794A DAC!  It introduces all the taste of tube on the sound. 

See last two pictures above.

I also attached the reference document for this Mu-Stage pre-amp.  I use the circuit in the last figure on page 9.  Enjoy!

Mu Stage Reference Document

I also take a FFT measurement as below: Output at 2Vrms 1kHz, filter 20 to 30kHz BW.

FFT measurement mu-stage preamp SE

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Everyone should own a 300B amplifier once in a life!  I am one of them.  This is quite a big and costy project and I use all the good stuff that I can afford at the time – Lundahl transformers, choke, Jensen Cap, Elna caps, Multi-cap, Rifa cap, telfon wires and Full Music 300B tube etc…  Total spend on that is about US$1200!

Full music tube is lack of bass.  Recently I buy a Quiguang 4300B and the bass is much better and firm.  The 4300B cost about US$120 per pair.  I think 300B to drive mid and high frequency is one of the best sound amplifier!

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Update: Oct 1st, 2010

The 300B was upgraded with Russian PIOs, see first picture.  FFT measurement is attached below:

FFT 300B final

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