I've completed a preliminary design for a specialized power supply that is essentially a DC audio amp (output voltage +-50, output current +-5A). Now I'm trying to figure out what hardware I'll need.
I figure that the output transistors going at full tilt could dissipate as much as 150W, so I'm guessing that a heat sink good for about 300W should be a conservative choice. Where might I find such an animal? Any other comments?
Related: I want to use TO-3 sockets, since I'm using 2n3773 and 2n6609 output transistors. Newark Electronics has one for $1.22 in quantity that seems OK (https://www.newark.com/keystone/4602/transistor-socket-3-position-through/dp/35F1178). I also found a batch of bakelite sockets on Ebay that appear OK. Any suggestions?
I figure that the output transistors going at full tilt could dissipate as much as 150W, so I'm guessing that a heat sink good for about 300W should be a conservative choice. Where might I find such an animal? Any other comments?
Related: I want to use TO-3 sockets, since I'm using 2n3773 and 2n6609 output transistors. Newark Electronics has one for $1.22 in quantity that seems OK (https://www.newark.com/keystone/4602/transistor-socket-3-position-through/dp/35F1178). I also found a batch of bakelite sockets on Ebay that appear OK. Any suggestions?
Why do you want transistor sockets? Do you think that power transistors need to be replaced, resembling power tubes? These sockets don't contribute anything positive to your built's reliability.
Best regards!
Best regards!
Well, I just thought that that's the proper way to mount the power transistors. I hadn't thought about soldering directly to the pins.
I have a Dynaco Stereo 400 amp I built nearly 50 years ago, which used sockets. I guess I'm remembering that.
As for replacing the devices, I'm hoping that I'll never have to do that.
I have a Dynaco Stereo 400 amp I built nearly 50 years ago, which used sockets. I guess I'm remembering that.
As for replacing the devices, I'm hoping that I'll never have to do that.
what happens to the power dissipation if you accidently short the outputs of the power supply? It will happen.
Manufacturers found over the decades that sockets lost contact with the base pin, due to oxidation. Oxygen never sleeps. They also limit heat transfer to a sink above the phenolic, which can't be very big.
Heatsinksusa sells sinks, operates down in the vendor section. I buy at newark some, and while their list prices on heat sinks are as bad as digikey & mouser, they do have sales. Look for the asterisk. If you use upper & lower limit function of selector table you can find something that is not quite what you planned but at 1/3 the price.
Best bargain in heat sinks is a blown up PA or guitar amp within 100 miles of your location. Freight is a killer on used equipment, but I got a blown PV-4c once for $28 on ebay. Took $80 to reactivate & improve it. (lower temp thermal cutout, more heat sink fins). I bought a blown PV-1.3k for $55 and brought it home on the city bus for $3 shipping.
When you're trying to regulate at +-50V, power per TO-3 device hits 80W when you short the output to GND. I'm using 5 devices in parallel top and bottom, hence about 400W total to the heat sink. The devices are always within the Safe Operating Area. That's 5 each, 2N3773 and 2N6609.
Under anticipated maximum load (say, 10 ohms and +-27V) PD per device peaks at about 16W.
I'm trying to avoid implementing current foldback, which would add a lot of probably unnecessary complication.
@indianajo I always enjoy reading your posts. You bring a lot of wisdom, experience, and plain common sense to the table.
Direct soldering is the best design, and used in all the amps that have survived through the decades without failures from oxidized connectors.
5 in parallel is good. I have a +-35volt @5amps. Adjustable current and voltage. I only use 2 in parallell. Fans are an option.
It might be worth considering a silent fan to cool the heatsink too - trying to assemble heatsinks around/below 0.1*/W isn't easy but with a light breeze ...
Indinanajo,
your 1st sentence is right. It covers exactly what I meant before. Anyway, the 2nd one doesn't apply, 'cause the sockets are mount at the heatsink's other side.
Best regards!
I have been using gold plated D-Sub socket for TO-3 pins on workbench amps. Do you guys think this would also be a bad idea for final amps?
86563004064LF Amphenol FCI | Mouser
86563004064LF Amphenol FCI | Mouser
i have been building to3 based amps for 40 years and didnt know you could buy sockets.
unless you do something silly like short the output they are generally reliable soldered.
unless you do something silly like short the output they are generally reliable soldered.