Please tell me how to upgrade Music Angel KT88 amplifier? - diyAudio
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Old 11th October 2005, 09:04 AM   #1
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Default please tell me how to up grade music angle kt88 amplifier ?

i bought a chinese made music angle kt88 tube amplifier from ebay store at $ 430 usa dollars , it is a 2 power supplys and 2 mono block which combined in a box, good sound , full of power 65w,

please tell me how to up grade it and replace the kt88.

thank you.
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Old 11th October 2005, 10:52 AM   #2
EC8010 is offline EC8010  United Kingdom
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Do a search and you will find that there was a thread recently about "Music Angel" amplifiers. As I recall, their quality control wasn't too good, so it may be worth opening them up and checking that they have been made correctly.
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Old 12th October 2005, 07:22 AM   #3
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Without seeing the circuit I can ONLY ASSUME its similar to the EL34 Music Angel. See this thread:
My Experience with "Music Angel" EL34 PP
I found that the phase splitter was the limiting part of the circuit due to poor choice of phase splitter design AND a production fault.
I also had good results from tube rolling - ditch the chinese 6N8P and substitute a 6SN7 (I used modern production Electroharmonix Gold). Input tube on the EL34 version was a 6N1P - I substituted a "Winged C" Svetlana. I also found that JJ EL34s were far superior to the standard chinese EL34s. I haven't tried the JJ KT88s but have heard from someone who has that they are very good.

I redesigned/rebuilt the phase splitter by replacing the anode load resistors with equal value resistors and substituted a LED referenced cascode current source in place of the tail resistor and while I was at it I doubled the current in the tube. ALL of the Music Angel circuits I've seen (and I have the EL34 PP and the 845 SET models) run the 6N8Ps at very low currents.

Can you post a schematic - probably available at the "eaudioguy" website.

Cheers,
Ian
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Old 2nd November 2005, 04:53 PM   #4
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See if we are lucky this time.

The KT88 scheme:
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File Type: jpeg ed_3_kt88.jpeg (62.6 KB, 1573 views)
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Old 2nd November 2005, 09:38 PM   #5
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Thanks Skorpion,

Hififactory,
The circuit is not the same as the Music Angel EL34 so some of my comments above are not relevant.

Actually its a YAW.n "Yet Another Williamson". There is more information on upgrading the Williamson design around the net than you can probably get through in a year.

Make sure you are running in Triode Mode for a start. On the switch which selects Triode / Tetrode Mode the position which is quieter (but more refined) is the Triode position. You CAN switch between the two with the amp running BUT its perhaps not a good idea to do it at full power.

On the schematic bottom right hand side you will see a 100K potentiometer and "-> A" this is the output tube bias adjustment.
Just one adjustment for both tubes so it important to use matched pairs. You would want to do both channels so its best to buy a matched quad. Each KT88 has a 12 Ohm resistor in the cathode.

Exactly 1 volt across a 12 Ohm resistor means 83 mA bias current and I am guessing that that is the correct bias setting.

Check first - measure the high voltage at the KT88 anode. For 35 Watts dissipation divide 35 by the high voltage reading to give the bias current to set. Multiply that current by 12 to get the voltage reading across the 12 Ohms cathode resistor and then adjust the bias potentiometer to give that reading. For long tube life you may want to set for 32 or 33 Watts rather than 35.

The value of the KT88 grid 1 resistor is 221K Ohms and this means that you should NOT run more than 35W anode dissipation even though the KT88 is capable (with smaller grid 1 resistance) of a maximum of 42 Watts.


Cheers,
Ian
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Old 2nd November 2005, 10:20 PM   #6
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It looks like the Power Supply Board is common to both the EL34 and KT88 Amps in which case the bias adjustment potentiometers are the one closest to the front of the board (one channel) and the one closest to the back of the board (the other channel).

Cheers,
Ian
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Old 3rd November 2005, 02:07 PM   #7
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Default hi, thank you

i moded my el34 music angle amplifier 2 days ago. i cut off the 6e2 tube , then, the sound is so wonderful now, it is unbelieveable ......... please try it ....... but be careful ...... make sure ..... step by step .....

now , i want to buy a music angle 845 amplifier, single end design, i found out one in ebay too = ebay store name :

hotproductstore, there are some 845 amps over there .....

with nice photos

thank you

good day
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Old 3rd November 2005, 06:54 PM   #8
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Quote:
Originally posted by gingertube
I haven't tried the JJ KT88s but have heard from someone who has that they are very good.

Hi there...yes JJ88's (in blue/yellow boxes) can deliver the power........however when compared to other "good newish brands" they hold up power well......but at a slightly higher thd compared to GLion types esp in UL mode.
The only thing against..... is the shape of the glass envelope (I don't like it) ....but so are other things in life.

richj
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Old 4th November 2005, 08:55 AM   #9
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Gingertube,

Judging from experience and schematics would you prefer the
EL34 or KT88 of the Music Angel amps ?

Your opinion would be appreciated !
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Old 5th November 2005, 06:44 PM   #10
gemby is offline gemby  Croatia
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I just boght one of those: http://cgi.ebay.com/Upgradeable-Valv...QQcmdZViewItem

Has anyone has schematics or some upgrading tips? Form first sight, schematics must be similar to Music Angel el34
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