WTF pictures of amps!

[Moleculo]

Many an amp i have repaired never had screw holes countersunk

I've seen that one also. For those reading the thread that may be wondering why that is important: If you just drill the hole and use a sheet metal screw (or whatever) straight into the heat sink, as the screw starts to get tight, the threads of the screw actually lift the tabs and transistor off of the heat sink. Of course, now the heat sink isn't doing much.

And wow...toothpaste.....now I know I've heard it all

 

[Captain Kilowatt]

I thought you only used toothpaste when building cavity filters. :w00t:

 

[mackmobile43]

Its a good idea to have braided straps across the grounds (emitters).
The alternative is to have ground connection to the bottom of the board, and the bottom layer is a solid ground. The board though must be plated thru with "vias".

Whats more important is what you cant see, like the proper tuning for efficiency, and how well the pills are mounted to the heatsink for good thermal transfer.[/quote]
Yes but not everyone will bother to lap the heatsink for that to occur, but I do.

 

[psycho]

Many an amp i have repaired never had screw holes countersunk. Sad but true. LOL had one guy near me building amps and never heard of thermal grease, so he used tooth paste. True story (Dillion built). I remember cussing repairing that amp.

Here is an EastCoast amp....no wonder he is out of business. Notice he used counter sink wood screws to secure the transistors. The picture is a little blurred but the amp just look worse with a better quality picture.

 

[Crusher]

Here is an EastCoast amp....no wonder he is out of business. Notice he used counter sink wood screws to secure the transistors. The picture is a little blurred but the amp just look worse with a better quality picture.

I had a 2x8 that looked just like that psycho. Not only that, but the input and output leads with absolutely no sheilding of and kind were literally laying ontop of each other. No wonder box kept oscillating and blowing pills. I had my work cut out for me trying to get that box up to par. I had to move alot of stuff around.

 

[Crusher]

I've seen that one also. For those reading the thread that may be wondering why that is important: If you just drill the hole and use a sheet metal screw (or whatever) straight into the heat sink, as the screw starts to get tight, the threads of the screw actually lift the tabs and transistor off of the heat sink. Of course, now the heat sink isn't doing much.

And wow...toothpaste.....now I know I've heard it all

The same guy that did this, when he built an amp was a copy of a copy. I don't even think he knew how to tune a box. He just saw somebody else's amp and put it together. Calling it good. These were literally thrown together.

 

[Happy_Hamer]

Sheet metal screws??????????????? CMON NOW??????

 

[mackmobile43]

Sheet metal screws??????????????? CMON NOW??????

They're much easier than drilling an tapping the 440 holes. My wrist still aches.

 

[Crusher]

I like the self tapping 4-40 screws. I get mine from Fastenal. Matter of fact, you can get any kind of bolt, screw, whatever you need. I have to go there later to pick up a bunch of stainless hex lockwashers. (the star type)

 

[Tallman]

I like the self tapping 4-40 screws. I get mine from Fastenal. Matter of fact, you can get any kind of bolt, screw, whatever you need. I have to go there later to pick up a bunch of stainless hex lockwashers. (the star type)

Just a few degrees of rotation with a 4-40 can make the difference of a good thermal joint or one that will cook your transistor.
Since the pitch of the thread of the sheet metal screw is steeper than the machine screw a fraction of a degree can make that difference.
I would use self tapping over sheet metal screws any day of the week as long as it is not going into a blind hole. Blind hole would be okay as long as it is 1.5 times the length of the screw.

 

[KD2GOE]

drywall screws

 

[Stellasarat]

Many an amp i have repaired never had screw holes countersunk. Sad but true. LOL had one guy near me building amps and never heard of thermal grease, so he used tooth paste. True story (Dillion built). I remember cussing repairing that amp.

Did thay come with an oral B

 

[Captain Kilowatt]

Just a few degrees of rotation with a 4-40 can make the difference of a good thermal joint or one that will cook your transistor.
Since the pitch of the thread of the sheet metal screw is steeper than the machine screw a fraction of a degree can make that difference.
I would use self tapping over sheet metal screws any day of the week as long as it is not going into a blind hole. Blind hole would be okay as long as it is 1.5 times the length of the screw.

I prefer to pull out the tap and die set along with some tapping fluid and do it the right way. Self tapping screws are fine in the right application however I don't think this is one of them. I just recently had to tap some holes in a rather huge aluminum heat sink. I had to make some 10-32 and a couple 4-40 hole both thru and blind and although aluminum is a pain to tap, using a good sharp tap and the proper fluid makes it easier and creates nice smooth threads. Follow up with a little counter sinking and the job is hard to beat.

 

[Tallman]

I agree completely. Nothing beats a blind hole done properly with a bottoming tap. but I think you might agree that self tapping machine screws are better than sheet metal screws.

 

[GnG8d]

An easy way to tap a hole square to the mounting surface is to make up a little guide. Take a piece of material in a drill press or mill and drill a thru hole just large enough for the tap to slide thru. Set your guide on the surface to be tapped and line up your through hole to the one being tapped. When you start spinning the tap into the threaded hole the guide will help you stay square.

The guide can be steel, aluminum etc, but don't hand drill it. Put it in a machine so it's square. The shape or size isn't critical, but rectangular and large enough to hold solidly works well.

Also back your tap off every 1/2 turn to break the chips.