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Old 26th February 2008, 07:57 PM   #1
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Default Mikale Abdellah SE KT88 B+ voltage?

I have spare 360-0-360 tranny. I would like to build SE KT88 with fixed bias. This tranny will giveme about 440V under the load. Is it too much HIGH for the Mikael Abdellahs design?

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Old 26th February 2008, 10:02 PM   #2
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Wirewound power resistors work for me
I hate to throw away power using this method, but it does work.
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Old 26th February 2008, 10:15 PM   #3
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Yes, it does work, but more you drop (bigger resistor) the more is the sound worse - more compressed and brighter, not so dynamic, fast and punchy. Even 100 Ohm has clear audible effect on sound quality.
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Old 26th February 2008, 11:22 PM   #4
alexg is offline alexg  Philippines
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Default Re: Mikale Abdellah SE KT88 B+ voltage?

Quote:
Originally posted by kacernator
I have spare 360-0-360 tranny. I would like to build SE KT88 with fixed bias. This tranny will giveme about 440V under the load. Is it too much HIGH for the Mikael Abdellahs design?

Scheme: http://diyaudioprojects.com/Schemati...-Amplifier.png
I built Mikael circuit using a 375-0-375 tranny. I used a 5u4gb rectifier which drops around 50V so it is perfect.

440V is a bit too high, but I think some members here have used up to 420V on Mikael's circuit.

Either use a tube rectifier or add another RC on your power supply if you really want 400V B+.

BTW, this amp sounds great! HTH
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Old 27th February 2008, 01:29 AM   #5
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Mikaels circuit is very similar to the SimpleSE. I recommend 375-0-375 volt power transformers for those amplifiers. B+ is about 430 to 440 volts with a 5AR4. Use a decent quality KT88 and it will work great. The best sound comes with a 5K ohm OPT with these B+ voltages. I have built one with a 400-0-400 volt transformer and a solid state rectifier. B+ is about 520 volts with an Electro Harmonix KT88 it absolutely rocks.

Mikaels circuit does not use fixed bias, it uses cathode bias.
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Old 27th February 2008, 02:33 AM   #6
-10db is offline -10db  United States
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Default Maybe rework the circuit for EL156 very similar...

the octal El156 is out: it likes that voltage with the 5k OPT.

So, take a look, the 6n1p will drive it fine.

Bias is only slightly different: less...

you will have a little more current in the OPT, and you will want to draw a little more current from the power transformer, but not much. Probably close to KT88.

Have a look thanks,
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Old 27th February 2008, 05:58 AM   #7
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Quote:
Originally posted by tubelab.com
Mikaels circuit is very similar to the SimpleSE. I recommend 375-0-375 volt power transformers for those amplifiers. B+ is about 430 to 440 volts with a 5AR4. Use a decent quality KT88 and it will work great. The best sound comes with a 5K ohm OPT with these B+ voltages. I have built one with a 400-0-400 volt transformer and a solid state rectifier. B+ is about 520 volts with an Electro Harmonix KT88 it absolutely rocks.

Mikaels circuit does not use fixed bias, it uses cathode bias.

I will be using SS rectifier too, so 450V on plates should be ok? What about the 6DJ8? Do I need to change something with this higher voltage?
I know that originial amp is cathode biasred but I want to make mine fixed bias as I like it more.
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Old 27th February 2008, 10:02 AM   #8
knubie is offline knubie  Norway
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Default Well within recommondation

Application data suggest from 340V too 540 V for ultralinear connection of KT88, and 5k Z-out.... So should be fine as it is...
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