• 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.

Mikale Abdellah SE KT88 B+ voltage?

kacernator said:
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/Schematics/images/Mikael-Abdellah-SE-KT88-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
 
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.
 
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,
-3db:cool:
 

kacernator

Member
2008-01-09 10:38 pm
tubelab.com said:
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.