• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

My KT88 SE project

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JesseG

JesseG

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Joined 2005
livingaudio.ca
#1
Hi all:

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


An externally hosted image should be here but it was not working when we last tested it.


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:
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Just starting construction

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Things well along

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Nearly done

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first power-up = measuring voltages and waiting for smoke

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In the room and making tunes - mighty good-sounding, if not overly powerful.

and the schematic
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#5
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 🙂



Are those Fostex TE166Es?
Click to expand...

Those look like Dave's tweaked FE127E.
Click to expand...

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. 😉
 
#8
what about cathode decoupling?
Click to expand...

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.
 
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