I prefer TO-247 or 263 transistors to replace TO3. Unless I have a heatsink already drilled for TO3. Drilling 4 holes accurately with my hand motor is not doable, IMHO. The plastic packages require 1 hole. Salvage motor drive or flat screen tv heat sinks will be pre-drilled for TO-247 or TO-263. Probably with long life silicon rubber pads already stuck to them.
The do-all of plastic output transistors is the MJL21193 pnp MJL21194 npn. Also avalable in prefix NJL and NJW and MJW, for reasons I can't determine from the datasheets. I use all four prefixes interchangeably, with .51 ohm emitter resistors to even current out.
The do-all of plastic output transistors is the MJL21193 pnp MJL21194 npn. Also avalable in prefix NJL and NJW and MJW, for reasons I can't determine from the datasheets. I use all four prefixes interchangeably, with .51 ohm emitter resistors to even current out.
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Hi, almost a year later and I have some different options for cooling.
First up, the four sinks a few posts back. They measure roughly 140x80x110mm each. So one sink for one pair of transistors.
The other option is the one attached. It measures 330x140x60mm and I can have it split into 4x parts 80x140x60mm with one for a pair of transistors.
If I runt the amp at the specifications provided by Audiosan
200VA 2x18Vac transformers and around 1.3A bias you will get around 25W class A @ 8ohm.
Is it your estimation that I could get away with either of the two options or is the latter to small?
First up, the four sinks a few posts back. They measure roughly 140x80x110mm each. So one sink for one pair of transistors.
The other option is the one attached. It measures 330x140x60mm and I can have it split into 4x parts 80x140x60mm with one for a pair of transistors.
If I runt the amp at the specifications provided by Audiosan
200VA 2x18Vac transformers and around 1.3A bias you will get around 25W class A @ 8ohm.
Is it your estimation that I could get away with either of the two options or is the latter to small?
Attachments
All should be fine for 2 TO247/263/TO3 pair of output transistors class A. Make sure the fins are vertical and airflow is not blocked.
Use a light bulb series the AC line to the transformer to prevent burnout of semis in case of problems. 60 w for this size amp. Use obsolete tungsten salvaged from somewhere. I have my light bulb socket in a grounded steel case with a breaker in case a wire pops off the socket and flies around. Edison base sockets with screws are designed for solid wire, not stranded.
If the light stays on, something is wrong. Look around at voltages with a DVM to find the problem. Don't use 2 hands measuring voltage, use an alligator clip lead on one probe. Voltage >25 from one hand to the other can stop your heart.