The On-Semi note does say that TO-3 cases are nearly impossible to warp through over-tightening, unless the moutning surface is badly bowed, but do recommend an alternating tightening sequence when a lot of force will be applied.
Another question: If some of the TO-3's will ba inaccessible from the back side, how will they be wired?
Another question: If some of the TO-3's will ba inaccessible from the back side, how will they be wired?
lgreen,
do we have a picture to look at to see what you are trying to do?
if you use the bar clamp idea, how would it be live? you isolate the TO-3 case from the heatsinks with a silicon pad or whatever, and he bar will simply be attached to the heatsink. it shouldnt be live.
there is an easy solution that doesnt need 5 pages if we could see a picture of what you are trying to do.
do we have a picture to look at to see what you are trying to do?
if you use the bar clamp idea, how would it be live? you isolate the TO-3 case from the heatsinks with a silicon pad or whatever, and he bar will simply be attached to the heatsink. it shouldnt be live.
there is an easy solution that doesnt need 5 pages if we could see a picture of what you are trying to do.
You would need to isolate the bar from the top of the To-3 package as well. I think you are asking for trouble by applying pressure to the top of the TO-3 case, which is not designed for it.
well, isolating the bar from the case isnt that hard, just use the same silicon washer on the other side too...
also, you can make a clamp that applies pressure to any part of the chip, even where it was designed to be clamped.
i used a bar clamp once that had a big screw right in the middle of it that hit the chip exactly where the mounting hole was. the scew applied pressure right at that very spot.
also, you can make a clamp that applies pressure to any part of the chip, even where it was designed to be clamped.
i used a bar clamp once that had a big screw right in the middle of it that hit the chip exactly where the mounting hole was. the scew applied pressure right at that very spot.
Time out here gents!
Lgreen are you going through all the trouble because someone was of the opinion that connecting T0-3's to a live heatsink was a bad idea? 😉
I'd still connect the TO-3's to the heatsink directly... there is a reason why it was designed that way.....
Just be careful of shorts prior to power up and keep the chassis enclosed.
Whoever is able to electrocute themselves over a piece of heatsink will do so over a bare array of TO-3 metal cans too...
My 2 c.
Lgreen are you going through all the trouble because someone was of the opinion that connecting T0-3's to a live heatsink was a bad idea? 😉
I'd still connect the TO-3's to the heatsink directly... there is a reason why it was designed that way.....
Just be careful of shorts prior to power up and keep the chassis enclosed.
Whoever is able to electrocute themselves over a piece of heatsink will do so over a bare array of TO-3 metal cans too...
My 2 c.
...assuming all TO-3's on the same heatsink are also on the same rail, and heatsink isolate from the rest of the chassis....
BrianDonegan said:
It is..... that is how his heatsink is designed. It is a pull out from an old industrial motor driver amplifier. All insulators are designed into the tunnel he has....
Pics
OK gents, here are the pics, reduced to 75K for those with dialup.
Below you see the Heat sinks with to-3 devices, one has a nylon washer and solder tab--
Note that this is not a very secure connection as mentioned earlier. Note that there are 2 mounting holes for the TO-3.
Below is a picture from the back, you see only one mounting hole due to the other.....
Being blocked as shown below in an end view.
Thus, its not practical to to drill out both holes because one is blocked; but the sinks are isolated from each other as you can see by the insulating green inserts; the bolts have insulating cylinders around them and I used nylon shoulder washers to secure the bolts to the metal bracket, so everything is very very carefully isolated from each other should I need to go live on the sinks. This was the orig plan until you all talked me out of it.
If the sinks are live the aluminum resistor casings also will be live, but they are isolated from the actual resistors so I don't think this will be a problem. Right?
Each collector will be run at the same DC voltage so its OK to have them live from that perspective.
So, its either go with live heatsinks or figure out how to mount them in a non-live situation by drilling out the TO-3 holes or some other means...
cowanrg said:
OK gents, here are the pics, reduced to 75K for those with dialup.
Below you see the Heat sinks with to-3 devices, one has a nylon washer and solder tab--
Note that this is not a very secure connection as mentioned earlier. Note that there are 2 mounting holes for the TO-3.
An externally hosted image should be here but it was not working when we last tested it.
Below is a picture from the back, you see only one mounting hole due to the other.....
An externally hosted image should be here but it was not working when we last tested it.
Being blocked as shown below in an end view.
An externally hosted image should be here but it was not working when we last tested it.
Thus, its not practical to to drill out both holes because one is blocked; but the sinks are isolated from each other as you can see by the insulating green inserts; the bolts have insulating cylinders around them and I used nylon shoulder washers to secure the bolts to the metal bracket, so everything is very very carefully isolated from each other should I need to go live on the sinks. This was the orig plan until you all talked me out of it.
If the sinks are live the aluminum resistor casings also will be live, but they are isolated from the actual resistors so I don't think this will be a problem. Right?
Each collector will be run at the same DC voltage so its OK to have them live from that perspective.
So, its either go with live heatsinks or figure out how to mount them in a non-live situation by drilling out the TO-3 holes or some other means...
The nylon screws will not hold well... the alternative has few advantages but more disadvanatges...
Lgreen, go with it as is... this is good!
🙂
Lgreen, go with it as is... this is good!
🙂
Have you stated what amp you are using these in? If you go with live heatsinks, the collectors are running at rail voltage. That means from heatsink to heatsink you will have double the rail voltage. In some amps that can be almost 200VDC. Seems like a good way to get shocked. My Soundcraftsmen amps all run live heatsinks but they are MOSFET's and so the heatsinks are actually the same voltage as the outputs.
Myself, I'd be drilling out the holes on the TO-3s for shoulder washers. Should be quite simple.
Blessings, Terry
Myself, I'd be drilling out the holes on the TO-3s for shoulder washers. Should be quite simple.
Blessings, Terry
Terry,
it is for the KSA-50 klone... 36 vdc rails not 100.
Also any rails need to be enclosed in the chassis and not left out in the open as with any electrical circuit... Safety helps... paranoia impedes. 😉
it is for the KSA-50 klone... 36 vdc rails not 100.
Also any rails need to be enclosed in the chassis and not left out in the open as with any electrical circuit... Safety helps... paranoia impedes. 😉
K-amps said:
Wow, he's using 4 pair of TO-3s per channel for his KSA 50?
OK, for 36 V rails he would only have 72VDC across the heatsinks. Still seems like that could bite you pretty good. I do'n mean to seem pardoid, just seems easier to isolate the transistors then the heatsinks. I guess if they are alread isolated then that's taken care of.
This thread was intitled "Expanding TO-3 Holes". I guess I was stuck on that direction. 😀
Blessings, Terry
Put heat shrink tubing around the screw and shrink. Experiment to find the proper length of tubing to use.
cloning
That's right, 4 TO-3's per rail (8 per channel) for a krell KSA 50 clone. 36 VDC rails. And I've got room for 6 per rail but I'm not totally nuts.
All the suggestions are good, I'll try drilling a few sample TO-3's to see how difficult it is, heatshrinking the screws and heatshrinking some countersunk screws.
Will heatshrink be ok if its in contact with some very hot heat sinks?
That's right, 4 TO-3's per rail (8 per channel) for a krell KSA 50 clone. 36 VDC rails. And I've got room for 6 per rail but I'm not totally nuts.
All the suggestions are good, I'll try drilling a few sample TO-3's to see how difficult it is, heatshrinking the screws and heatshrinking some countersunk screws.
Will heatshrink be ok if its in contact with some very hot heat sinks?
Yes, unless your heatsinks get REALLY hot, in which case you are more concerned about the transistors. Use good quality heatshrink from 3M or the like.
Wht not lightly oil the screws, fill the tapped holes with decent quality (metal loaded?) epoxy and insert screws? When the epoxy's set, the screws can be threaded out and the trannies fitted.
If in doubt, degrease the existing holes first to ensure good adhesion, and use the TO3s to support the screws whilst the resin's setting to ensure that they're square - in which case you will need slightly longer screws initially to ensure that the permanent ones don't bottom out when tightened.
Similar method's worked for me in a number of applications.
If in doubt, degrease the existing holes first to ensure good adhesion, and use the TO3s to support the screws whilst the resin's setting to ensure that they're square - in which case you will need slightly longer screws initially to ensure that the permanent ones don't bottom out when tightened.
Similar method's worked for me in a number of applications.
At least you don't need to expand both holes on TO-3 package. Do only one side (each) and use 4-40 screws with nuts on the other end.
Be careful when drilling holes in transistors, depending on equipment used and your skills, it may affect flatness of the case. I'd recommend vise with a special jig, and low speed drill press.
Be careful when drilling holes in transistors, depending on equipment used and your skills, it may affect flatness of the case. I'd recommend vise with a special jig, and low speed drill press.
Re: cloning
Seems to me that the problem has become more important than the solution on this thread.
Why not go K-amps way : you've already done the labor on the heatsinks to isolate them.
If it is all that difficult to modify the heatsinks or the TO3's, why not leave it as is, and wait for the endresult .
Should you encounter problems when the ksa is finished, you'd still have the option of getting them insulated the hard way.
Who knows, your KSA50 may function great, and you can up the bias to mega level.
We might even be jealous of your rig !!
lgreen said:
Seems to me that the problem has become more important than the solution on this thread.
Why not go K-amps way : you've already done the labor on the heatsinks to isolate them.
If it is all that difficult to modify the heatsinks or the TO3's, why not leave it as is, and wait for the endresult .
Should you encounter problems when the ksa is finished, you'd still have the option of getting them insulated the hard way.
Who knows, your KSA50 may function great, and you can up the bias to mega level.
We might even be jealous of your rig !!
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