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mounting 2N3055 to a heatsink?

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HM_Murdock

Wed Aug 11 2010, 02:27AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Apologies for asking such noob questions, but I swear I have googled this till I am cross-eyed...

Looking for advice on the best way to mount a 2N3055 (or any TO-3 type?) to a heatsink.

1) Drilling the holes in the heatsink: do you guys drill one big hole for the emitter and base poles (if that's the right term), or do you drill 2 smaller well-placed holes to maximize contact with the heatsink to the insulator?

2) Insulators: I have seen the mica and silicone mounting kits...which works better? I have read the silicone doesn't need thermal paste, but I have no experience with either of these insulators.

3) Attaching the wires to the emitter and base: Do you solder right to them, or is there some sort of connector?

Thanks in advance for help on this...

dmg

Wed Aug 11 2010, 02:35AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

HM_Murdock wrote ...

1) Drilling the holes in the heatsink: do you guys drill one big hole for the emitter and base poles (if that's the right term), or do you drill 2 smaller well-placed holes to maximize contact with the heatsink to the insulator?

I personally just drill 2 holes about 5MM or so in diameter, and 2 more holes for the mounting tabs.

HM_Murdock wrote ...

2) Insulators: I have seen the mica and silicone mounting kits...which works better? I have read the silicone doesn't need thermal paste, but I have no experience with either of these insulators.

Ive found the silicon pads to work quite well, they need no specail setup, all I do is cut them to size (a square or so) then just poke holes into it with the 2 leads, and mount away. but note that you will need some plastic bolts if you want to isolate the case when you mount its side holes. or you can use thin metal bolts, as long as they have a plastic washer, and do not create a contact between the sink and the transistor.

if the package does not need to be isolated, just thermal grease will do.

if you dont want to bother with silicon pads, you can always use regular grease, then isolate the heatsink using insulators for the heatsink mounts itself, or mounting it on some plastic or something.

HM_Murdock wrote ...

3) Attaching the wires to the emitter and base: Do you solder right to them, or is there some sort of connector?

I solder them right onto the leads and then cover the solders with either heatshrink or some electrical PVC tape (black). I havent heard of a connector made for these leads before, so I dont know about that one.

hope that helps you out a bit

radiotech

Wed Aug 11 2010, 04:10AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

If you removed that 2N3055 from some old gear, or got hold of an old mounting kit look at this : Also there is a thread on 4hv concernig this.

klugesmith

Wed Aug 11 2010, 05:17AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

HM_Murdock wrote ...
3) Attaching the wires to the emitter and base: Do you solder right to them, or is there some sort of connector?

The TO-3 pin diameter is typically 0.040 inches (1.0 mm), same as male DB-9 and DB-25 connectors that used to be standard PC serial and parallel ports. You can use pin receptacles from female DB connectors, soldered to stranded hookup wire and insulated with a bit of heat-shrink tubing.

Direct soldering of wires to TO-3 pins is faster, and won't hurt the part if you are reasonably good at it. The time savings is lost if you need to replace the part, or change it experimentally.

radiotech

Wed Aug 11 2010, 06:07AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

We did have sockets for those things back then. Made repairs a tad easier.

HM_Murdock

Wed Aug 11 2010, 03:10PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Great info...just what I was looking for!

Thanks for the heads-up on the older ones...this is for a new transistor, not a scavenged one (new at Radio Shack for $1.90). Sounds like money well spent as deadly as the dust from those old insulators is.

I like the idea with the DB connector pins...got plenty of old connectors and cables laying around.

As for the silicone pads, sounds like you are buying them by the sheet? Is there a DIY substitute, or is this a particular type of silicone sheet specially made for the application?

I have also read where if it is a single transistor setup on the heatsink, you do not need to insulate the transistor from the heatsink...is this true, and will doing this result in a charged heatsink?

Thanks again guys...HUGE help on this...

IntraWinding

Thu Aug 12 2010, 06:28AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

radiotech wrote ...

If you removed that 2N3055 from some old gear, or got hold of an old mounting kit look at this : Also there is a thread on 4hv concernig this.

I've started a separate thread asking how to distinguish insulators made of Beryllium and Aluminium Oxides

HM_Murdock

Thu Aug 12 2010, 12:25PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

I have order a couple of these, will see how they work out. Claims all parts needed for easy mounting and no soldering done to the transistor, so changing them out is easy if I fry one...not bad for $1.60.

TO-3 Socket Kit

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