Tuesday, May 12, 2009

Oumeidanji KT-88 Valve Amplifier.

The Oumeidanji KT-88 Valve Amplifier is a unique amplifier since it is capable of using the KT-88, 6550 or the EL-34 tubes in the same amplifier. The amplifier was designed as a small integrated for driving a pair of speakers and it does support a headphone amplifier out with an impedance of between 300 - 600 ohms. I would not recommend to drive headphones of lower impedance since it would become a burden on the amplifier. The amplifier runs in Class A and once warmed up it does run hot, so strongly ventilated areas are recommended. Since the amplifier will drive 300-600 ohm cans, these are well suited to the likes of by Darth Beyers or other Beyer Dynamic headphones.

Driving the pair of KT-88 are a pair of Chinese 6J8P tubes, and I did not bother with these. The western equivalents are the 6SJ7 or the premium 5693 metal cans. From the photos below you can see that I rolled the amplifier at first with a pair of RCA NIB NOS 6SJ7 matched pairs and then a pair of General Electric 5693 matched pair "Red Tubes". A note about the "Red Tubes", regardless of what brand you find imprinted on them, all "Red Tubes" are manufactured by RCA.

Whist the Black Metal RCA 6SJ7 Tubes were good, they were sonically no match for the superior "Red Tubes" and this accounts for the vast difference in price between the two in the market place.

The supplied pair of KT-88 tubes are from "Shuguang" of China, but I am very likely to change these to a pair of "Gold Lions" in the near future.

RCA 5693 "Special Red" Tubes

Replaces 6J8P, 6SJ7, and 6SJ7GT tube types. The RCA "Red" tubes (5690, 5691, 5692, 5693) were designed for 10,000 hours of use. RCA claimed the 5693 tube could withstand shocks of 100 G's for extended periods of time! These are the best upgrade tubes for this amp.

Photos below show the amplifier rolled with the General Electric 5693 "Red Tubes" which are NOS matched pairs.

In fact regardless of what brand is printed on these red metal cans, all the "Red Tubes" were manufactured by RCA.

The "5693 Red Tubes" are sonically superior to the 6SJ7 Black Metal Tubes and of course far superior to the stock 6J8P which I did not even bother with.

The Specs:

  • Shuguang KT88 X 2 , 6J8P X 2
  • Output Impedance : 8 ohm
  • Output Power :2 x 10 W (Class A)
  • Earphone Output Impedance 300-600 ohm
  • Frequency Response:5HZ-200KHZ
  • T.H.D. <>
  • Length 160mmx Height 170mmx Depth 320mm
  • Weight: 9kg
  • Color :Black
  • Power: Switchable 110V - 240V (50Hz -60Hz)
Review CD's:

1. Audiophile "Timeless Best Collection" 24 bit / 96khz DSP Mastering URCD;
2. Wild Blue "Jeanne Newhall";
3. We Miss You, Leslie "Chris Babida";
4. Dark Side of the Moon "Pink Floyd";
5. Tubular Bells "Mike Oldfield";
6. Variations "Andrew Lloyd Webber";
7. Hotel California "Eagles" - Japanese CD pressing;
8. 2AM "Danny Summer" XRCD;
9. Natural Elements "Acoustic Alchemy";
10.Breakdown "Paulinho Da Costa";
11.Gold Lion KT88 Vacuum Tube Audiophile Recordings "HECM - Musical Fedelity Recording";
12.Eternity "Angella Christie";
13.Hi-End Audiophile Test Demo "HD Mastering - ABC Recordings";
14.The Tube Hi-Fi Saxaphone " High Resolution Tube Recording - ABC Recordings";
15.Headphone Test Disc "ABC Recordings";
16.Memorial Version 30 years - Tubes "ABC Recordings";
17.Luxman 2009 Demonstration Disc " DSD recording";
18.Blue Skies "Stan Getz";
19.vol.SOUND "S.E.N.S."

Update 1: 30th May, 2009

Burn in is approaching close to 90 plus hours and the amplifier appears to be beginning to open up, the red tubes make a substantial difference to the overall timbre and sonic performance of the amplifier. I have still yet to decide on rolling of the KT-88 tubes and will leave them for now. I can hear the bag end (bass) tightening up and becoming better controlled. Once I near the 150 hour burn in mark I will report again. One thing, this is an amp for 300-600 ohm phones and it does not like the low impedance types - you will hear some hum with the low impedance phones. Phones in the right category work great with it!

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