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-   -   My KT88 SE project (http://www.diyaudio.com/forums/tubes-valves/120783-my-kt88-se-project.html)

JesseG 4th April 2008 10:18 PM

My KT88 SE project
 
Hi all:

It is up and runing, so I thought I would share this project with you all.


http://www.livingaudio.ca/photos/kt88-10sm.jpg

It is a single-ended KT88 in Triode mode, with a 6DJ8 SRPP driver stage, James OPTs and a HUGE power supply made from trafo and chokes rescued from some very classy radio equipment.

The whole thing is built on an open-frame chassis made from 1/2-inch (yes, thats 13mm) aluminium plate. All up it weighs about 55lbs.

Construction is very straightforward. However the power supply is a bit wierd. The Trafo outputs 375-0-375. Since I did not have room on the chassis for a rectifier tube, and SS rect. brings the voltage up so high that I would not have been able to use reasonable value caps, (plus, I had 2 chokes) I decided to split the output of the trafo into 2 seperate half-wave supplies.

The result is a seperate supply for each channel, which share a trafo secondary. So an almost doal-mono design ;)

Some more photos:
http://www.livingaudio.ca/photos/KT88-2sm.jpg
Just starting construction

http://www.livingaudio.ca/photos/KT88-5sm.jpg
Things well along

http://www.livingaudio.ca/photos/KT88-7sm.jpg
Nearly done

http://www.livingaudio.ca/photos/KT88-8sm.jpg
first power-up = measuring voltages and waiting for smoke

http://www.livingaudio.ca/photos/KT88-9sm.jpg
In the room and making tunes - mighty good-sounding, if not overly powerful.

and the schematic
http://www.livingaudio.ca/photos/MY SET KT88.gif

hotbottle 4th April 2008 11:26 PM

Looks great.

- glad I wasn't punching the chassis holes though ;)

Psychobiker 5th April 2008 01:09 AM

I've got the lovely task of makign my chassis holes soon....but thankfully I'm only dealing with ~1.5mm!

Are those Fostex TE166Es?

gmilitano 5th April 2008 01:19 AM

Nice work Jesse.

Quote:

Originally posted by Psychobiker
Are those Fostex TE166Es?
Those look like Dave's tweaked FE127E.

JesseG 5th April 2008 02:19 AM

The holes were all drilled. The square holes that mount the trafo and chokes were drilled at the corners, then cut with a jigsaw, then filed smooth. Very time consuming and rather mad, really.

However, the chassis is nothing if not solid :)



Quote:

Are those Fostex TE166Es?
Quote:

Those look like Dave's tweaked FE127E.
They most certainly are Dave's enABleD FE127s.

BTW: Thanks very much, gmilitano, for the KT-88 SE you published on your site. It is the source for the KT-88 section of this amp. ;)

gmilitano 5th April 2008 03:06 AM

Quote:

Originally posted by JesseG
BTW: Thanks very much, gmilitano, for the KT-88 SE you published on your site. It is the source for the KT-88 section of this amp. ;)
Actually, that is Mikael Abdellah's Single Ended KT88 Tube Amplifier.

Here is Alex's Single Ended (SE) KT88 Tube Amplifier with a beefed up supply.

Cheers,
Gio

oldeurope 5th April 2008 12:58 PM

Hi JesseG,
well done, what about cathode decoupling?
Kind regards,
Darius

JesseG 7th April 2008 01:35 AM

Quote:

what about cathode decoupling?
Good eyes :)

I left off the cathode bypass for two reasons - 1) because I wanted to get a good idea of the effect on the sound with and without a cathode cap. and 2) because the schematic calls for a 220uf cap - I don't have any 220uf of any kind of quality right noiw and the idea of putting a cheap electryolytic in there just makes me cringe.

Right now, the amp sounds fantastic. When I can get some 220uF Black Gates (or similar) the I will try them.

Geek 20th April 2008 05:26 AM

Hi JesseG,

That looks super and that solid construction is wicked! :D

Is there a grid leak resistor on the KT88 not shown in the schematic?

Those speakers look familiar too ;)

Cheers!


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