This is not just another Aleph

[Peter Daniel]

Motivated by yesterday's posts, I started work on Aleph X monoblocks. Most of the parts comes from my A75 which was taken apart fot that purpose.

It looks like it's going to be one of a few not commercial Alephs with TO-3 output devices. Since A75 used 12N channel mosfets per channel and I'm using 16 I had to use extras from my stash. Just out of curiosity, I checked the price and it appears that I paid $2.36 for one IRF230 in 1994. How much are they today?

The caps on board are 1,500u Panasonic HFQ. I checked the values and after 8 years of usage they are still OK. There will be more caps outside the board and resistor or thermistor between. Total capacitance per channel 128,000uF.

The power would be around 100W, PS +/- 20V DC, I'm using 4 banks of 4 devices per channel. I am not quite sure about the source resistors value, but I would like to use the same I used in A75 which is 0.56 ohm. Anybody please correct me if I'm wrong. The current would be around 6A for both sides.

The heat sinks are the same as A75.

Please note attention to details, I'm not using screws to conduct the current, but rather Kimber wire soldered to mosfets cases.

[jleaman]

Looks nice Peter ..: O ) did you get them relays yet im wondering what were going to do for a trade..

[Nelson Pass]

I believe your math is all correct, and .56 ohms should
be just Jake.

[skaara]

Very interesting, cant wait so read your observations on its sound..

[Peter Daniel]

Me too.

A few more quotes. I paid $18.74 for one IRFP9240 in 1994 and $7.8 for IRFP048. They like 3 times less today.

This is how the board looks from the other side. Had to resolder almost half of it (half the electrolytics had to change polarity). I liked to make the traces for output stage this way. I was drawing the spaces with a marker on mylar and it was it, no fancy software, no gerber files. Picked that method from Yamaha, all their boards were design that way (minimum etching, maximum conductivity).

[kiwi_abroad]

How did you manage to solder to the T03 cases?. I've noticed before that that is almost impossible

Good luck with the project!!

Adrian

[skaara]

To solder to3 case, you have to "scratch" the surface where you want to solder the wire, and ou have to have a good soldering iron - because you have to heat up the case. Thats why a lot of ppl cant solder to to3, their soldering iron cools down, because it doesnt have good temperature distribution and not enough watts..

[Peter Daniel]

Since I was using 100W soldering iron, I didn't even had to scratch the surface.

[skaara]

I have a question too, why do you use plastic isolation for transistors? Doesnt the normal one have better heat conductance?

[Peter Daniel]

I hate using grease (especially when your amp has 48 output devices), and these ones were nice alternative to mica. They worked fine in A75 for last 8 years, so I didn't see a reason not to use them again.

Thermal impedance 1.13°C-in2/W (@50 psi)
Original sil-pad material
Excellent mechanical and physical characteristics
Flame retardant
Sil-Pad 400 is a composite of silicone rubber and fiberglass. It is flame retardant and is specially formulated for use as a thermally conductive insulator. Primary use is to electrically isolate power sources from heat sinks.

Sil-Pad 400 has excellent mechanical and physical characteristics. Surfaces are pliable and allow complete surface contact with excellent heat dissipation. Sil-Pad 400 actually improves its thermal resistance with age. The reinforcing fiberglass gives excellent cut-through resistance and Sil-Pad 400 is non-toxic and resists damage from cleaning agents.