Alternative 6 Watt Amplifier with EXICON Lateral MOSFET

[Ejam]

Tease us no longer!

 

[lineup]

Here is the power supply.
You need to have one 2x15VAC transformer 200-300VA.
Then some rectifying diode bridge, say 10A.
Then use 2 of this power supply. One for each channel.

As you can see the power supply output is at precise +/-14VDC.

 

[gary s]

That is good as I have some original NOS Hitachi 2SJ50/2SK135 in TO-3.

 

[e_fortier]

The difference in this amplifier is differential JFET input.
And also that it works in Single Ended pure Class A.
This means a very low effiency.
Amplifier draws almost 40 Watt to output only 6.8 Watt.
For having higher efffiency you must use Push-Pull and eventually Class AB.
Probably those amplifier you have listened to use that way.

About TO-3.
I will tell PCB files makers to not have transistor onto the PCB.
Instead it will be 3 pads and connected by wires.
Transistor on heatsink and 3 wires to the PCB.
This will make you to use any power transistors.

That sounds great for the pads instead of TO3 being attached to the PCBs. Indeed, all the amplifier I’ve heard using lateral Mosfet were Class AB.

 

[lineup]

Come on Lineup, time to give us a look at your schematic.....

Okay. Here it is. As long as I have come.

But there can be changes ... in small details.

 

[lineup]

That sounds great for the pads instead of TO3 being attached to the PCBs. Indeed, all the amplifier I’ve heard using lateral Mosfet were Class AB.

You are lucky to have TO-3 power transistors.
They are great for to handle lots of current and volt = Watt.
They can often have a temperature of 175 degrees, while TO-247 can only cope with 150 degrees.

 

[thirdicomplex]

Is R16 really necessary?

 

[lineup]

Probably not. It was used to get exactly 1.35A in output.

 

[thirdicomplex]

What's the idle current without it?

 

[lineup]

I am begining to be scared 🤔
One channel uses 38W to put into heatsink.
But there are 2 channels for stereo.
Means that the heatsink will have to get 76W out of the system ....
Can this be done?
I doubt it 😕
Maybe with 2 heatsinks - one for each channel.

 

[lineup]

What's the idle current without it?

1.34A
So the R16 is putting out only 0.01A more.
1.34A will of course be as well.

 

[thirdicomplex]

Maybe with 2 heatsinks - one for each channel.

No worries. That's how many chassis' for class A amps are setup for

 

[Vunce]

Nice shift in direction Lineup😉
Just for reference, the First Watt M2 clone amp generates approximately 70W of heat per channel. What's a few more watts, 76W is nooo prob 😂

 

[lineup]

The only matching necessary is for the input pair JFETs.
Even if they are not 100% matched it will work
because of the trimpot 100ohm at the sources of input pair.
Adjust trimpot to get zero offset in output.

 

[e_fortier]

If the dissipation at idle is 38W and considering a max heatsink temp of 50C, you would need a heatsink of 0.65C/W or lower for each channel. If you have an old Hafler DH-200 or 220 each heatsink is roughly 0.5C/W so a good match, the heatsink are also build to accommodate TO3...

 

[Extreme_Boky]

Psst... BUZ901/906 inTO3.

 

[Extreme_Boky]

About TO-3.
I will tell PCB files makers to not have transistor onto the PCB.
Instead it will be 3 pads and connected by wires.
Transistor on heatsink and 3 wires to the PCB.

I do not think that's a good idea.
One PCB for flatpack transistors; the second PCB for TO3 transistors.

 

[gary s]

BUZ901 are cool, but now obsolete and very expensive for the few left at certain distributors.

 

[lineup]

If the dissipation at idle is 38W and considering a max heatsink temp of 50C, you would need a heatsink of 0.65C/W or lower for each channel. If you have an old Hafler DH-200 or 220 each heatsink is roughly 0.5C/W so a good match, the heatsink are also build to accommodate TO3...

With a heatsink 1.0C/W and +30 degrees inside amplifier,
there would be 30 + 38*1.0 = 68 degrees one heatsink.

Then we need two of them 1.0C/W heatsinks.
0.65C/W is of course better. As you say +50 degrees.

 

[nicoch58]

You can add to the list of equivalents, Samelab ALF08 series, used in F7.

woow can be do an F7 with 2SK1058 !!? forgot