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KT88 OddBlock amplifier from scratch
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=1386
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Author:  Bennybuis [ 16 Jan 2010, 00:37 ]
Post subject:  KT88 OddBlock amplifier from scratch

Hallo everybody,

time for me to start a serious project. I have a quad of matched Sovtec
Attachment:
KT88 enclosure.jpg
KT88 with witch I wanna build the OddWatt mono blocks, just that I will fit everything in one enclosure, still building each channel starting with the PSU separately. Here are the specs of my power transformer:

Torodial 340VA Power
Pri: 0-115-230 V (gelb-weiss-grau/yellow-white-grey)
Sec 1: 350 V @ 0,4 A (rot-grĂ¼n/red-green)
Sec 2: 350 V @ 0,4 A (weiss-blau/white-blue)
Sec 3: 50 V @ 0,1 A (schwarz-schwarz/black-black)
Sec 4: 50 V @ 0,1 A (braun-braun/brown-brown)
Sec 5: 6,3 V @ 4,0 A (orange-orange)
Sec 6: 6,3 V @ 4,0 A (lila-lila/purple-purple)

Pretty nice, I can really build mono blocks in one enclosure. Here is the photo of the enclosure. don't know yet, if I will use that, it is depending on if I can fit everything nicely, but I am a wooden box fetishist, ha ha.

Author:  Bennybuis [ 16 Jan 2010, 00:42 ]
Post subject:  Re: KT88 OddBlock amplifier from scratch

Many thanks to Bruce Heran from OddWatt to make this possible and for helping me and countless others on a daily basis, and for answering my stupid questions so patiently and for calculating the ccs resistor for all my silly projects. Thanks Bruce.

This is the kt88 obbblock schematic I will use except that mine will have thermal delay tubes instead of a timer chip (OUCH)

Today my power transformer will arrive and I can see if everything fits. Will keep sending photos.

Author:  Bennybuis [ 16 Jan 2010, 02:29 ]
Post subject:  Re: KT88 OddBlock amplifier from scratch

Hallo everybody,

Attachment:
kt88.jpg


those are the tubes I will use. I hope, that they will stay balanced in this setup. Does anybody have experience with this tube?

Author:  nkdk [ 16 Jan 2010, 03:44 ]
Post subject:  Re: KT88 OddBlock amplifier from scratch

Hi Ben
Realy a very nice box you have for this project ,i think wood and tubes look nice.
I have no experience with the sovtek kt88 tubes , but normally sovtek perform very well.
What output tranny are you planning to use?.
nkdk

Author:  Bennybuis [ 16 Jan 2010, 05:35 ]
Post subject:  Re: KT88 OddBlock amplifier from scratch

Hallo everybody,

I will use Edcors, CXPP25-8-5K, they will do the job.

Author:  azazello [ 16 Jan 2010, 06:09 ]
Post subject:  Re: KT88 OddBlock amplifier from scratch

Ben!
Try to put switch for UL and triode mode /connect 2 grid to UL tap or to plate across R= 300 ohm/
and compare the sound.

Author:  Bennybuis [ 18 Jan 2010, 11:49 ]
Post subject:  Re: KT88 OddBlock amplifier from scratch

Hallo everybody,

well now I got it all in house except the 1st 4 filter caps, and those I will get tomorrow. I decided to not use my wooden enclosure, that stuff is too heavy and expensive, I got myself a nice and big Hammond case, tonight I will start putting it together, cutting holes for my KT88

Author:  azazello [ 18 Jan 2010, 12:11 ]
Post subject:  Re: KT88 OddBlock amplifier from scratch

Ben!
Put 2 and 3 KT88 on the left and right front corners, away from toroid.

Author:  Bennybuis [ 18 Jan 2010, 13:09 ]
Post subject:  Re: KT88 OddBlock amplifier from scratch

Thanks Azazello,

I am not quite ready to cut any holes, haven't decided to where things should go, I am still planning. It has to be the steel case, I love wood, but the power transformer is very heavy on it's own, and the Edvor output transformers are heavy, too. My wooden box will just break under it's weight, I am afraid. The CCS resistor for the LM317 on this amp is only 6,8 ohm, so the LM317 will get pretty warm, I need a good cooler, will get that tomorrow and the first 4 filter caps, rated to 500 volts. It's coming together, by the time it's weekend I will know how my Sovtek KT 88 will sound, I am excited. Here are more pics.,

Author:  azazello [ 18 Jan 2010, 13:51 ]
Post subject:  Re: KT88 OddBlock amplifier from scratch

Ben!
I'd advise You to use fast rect. diodes 4 pcs. BYV26E, it's almost like rect. tube.
It will better for sound.
/You have an Email/.

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