Stereo Build - Mikaels KT88 - diyAudio
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Old 22nd December 2006, 01:08 PM   #1
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Default Stereo Build - Mikaels KT88

Am well underway to getting this amp built now and am hoping to have it finished within the next few weeks.

I decided on a hammond 260m power transformer which is capable of 250mA to the B+ so should be more than ample for stereo kt88's For the output transformers i decided on james 6123hs and bought a matching james choke. Unfortunately the hammond was part of the "ugly" range of power tx's but hopefully wont look too bad come the end.

I can thouroughly recommend thlaudio for ordering components, its a bit of a pain ordering but prices, delivery and communication were very good.

I wanted the top mounting plate made from polished stainless, but i have little patience when it comes to cutting holes into 6mm steel so decided to get the thing laser cut

I drew the plate up in solidworks and then sent it off to be cut, now its back im very happy with the finish, the reflection is absolutely 100% and the reflection of the components can be seen perfectly.

For the base I am going to use a product called avonite, its a kind of fake granity looking resin. With the stainless resting on top of this the look is incredible - will try and find a camera later on today

Now going to start the electronics and get the mounting plate finished off and start assembling

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Old 22nd December 2006, 02:39 PM   #2
Sherman is offline Sherman  United States
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Great looking project so far! I heartily approve of your choice of the James OPTs. They are what I used on my monoblocks and they sound great (they look great also).

You should definitely have enough current capability with your PTX as well. I have my KT88s biased at 82mA and the 6N1Ps draw about 8mA (each triode, though I'm using two separate tubes of course due to the monoblock configuration).

I used 1/8" 6061 aluminum for my top plates and found it relatively easy to drill the holes. Stainless is a whole other animal!

I'm looking forward to seeing the finished amp!
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Old 22nd December 2006, 02:42 PM   #3
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Have just taken some pics, excuse the quality i cant find my proper camera!

Gives you some idea of how it will look, the base isnt made yet but will surround the stainless by about 12mm with the top being flush with it.

The 6n1p looks a little low, thats just cause i couldnt find a box big enough to rest it on

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Old 22nd December 2006, 02:45 PM   #4
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also I have a spare mounting plate if anyone from the UK could make any use of it!
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Old 22nd December 2006, 02:58 PM   #5
Sherman is offline Sherman  United States
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I like the base! I have a big piece of Corian laying around that I've thought of using as a base. After seeing your mockup I may pull it out and have a go.

For my amps I built a wooden base from maple and walnut dovetailed together. Also with a rebate around the top so the top plate sits flush.

I see you are also going with tube rectification, looks like a 5U4-G? If so be careful of the input cap in the filter, 40uF max in that position. (You may already be aware of this but I had to buy new caps, I had not paid enough attention to the datasheet and originally purchased 60uF for that position. )

Also my cheap Chinese 5U4-G tubes arced a bit on power up. No adverse affects that I could see but it was disconcerting so I changed them for Sovteks and the problem went away. I used the Chinese tubes in a lower current, lower voltage, lower value input cap EL84 amp and they have performed well for almost 2 years. Recently I put one in one of the KT88 monoblocks and it worked perfectly, no arcing, just a nice even warmup. Maybe they needed a break-in period?
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Old 22nd December 2006, 03:07 PM   #6
mr.duck is offline mr.duck  United Kingdom
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That mirror finish looks flawless! Where did you have it laser cut and was it expensive?
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Old 22nd December 2006, 03:07 PM   #7
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yes its a 5u4g and goes into a 40uf ---> 10H ---> 100uF

rectifier tube is a sovtek, jj kt88's and sventlana 6n1p iirc.

I was going to use wood but they joy of the avonite is that its very easy to get a perfect finish.
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Old 22nd December 2006, 03:12 PM   #8
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Quote:
Originally posted by mr.duck
That mirror finish looks flawless! Where did you have it laser cut and was it expensive?

Im happy with it My other sheet still has the protective filme on to help prevent scratches and will be the one i finally use.

Its a shame i cant find the camera, but if you look in the pics it looks equally as bad in the reflection as the real thing

My dad had somebody cut the stainless, i would have though in the region of 100 to have it cut and polished. Much much more if you didnt do the drawings yourself
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Old 23rd January 2007, 08:31 PM   #9
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Default Finished!

Got my finger out and finished it this afternoon and it worked perfectly first time, didnt blow any fuses!.

Very very happy with both the finish and the sound




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Old 23rd January 2007, 08:50 PM   #10
rdf is offline rdf  Canada
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Beautiful work.
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