• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Why pull and redo power transistors on the heatsink

Just my view... But I would bet that split washers were the state of the art back 45 years ago. And that 45 years from now the beveled washers will prove to have some other limitation...

They worked well for 20, 30 or more years of usage.. Then may have started to fail and loosen.

Not a big issue, just part of the normal wear process and all the more reason to your point to service the power transistor mounting after 45 years....

Mike Sweeney said:
Funny thing is that Marantz used split lock washers which they expressed said "don't use" :eek: I don't think they were going for max transfer.. it was probably more of "this will work" The 7 inch pounds is what I worked out yesterday reading up on things.. and I am guess most go way over when they tighten it up. 7 inch pound doesn't feel like very much
Click to expand...
 
FWIW, additional example information related to mounting. This is from Fairchild.

Sometimes spring clip mounting is viewed as cheap method but the constant tension/consistent force actually isn't such a bad idea.

index.php
 
Just an FYI ...most early US made units had aluminum case transistors and mounting screws/washers. Maybe all US units... That would reduce the issue of expansion rate differences and the need the for split/beveled washers? But those aluminum screws stripped easy....

I never thought of it.... Marantz did.... Or it was the standard back then.

Also, always thought the aluminum case power transistors were an out grow of aerospace requirements for light weight and high performance.... And fast warm up.... Some of there stuff does not get a chance to warm up before it gets used.... The avionics industry drove the state of the art for power transistors back then....

I would bet some bean counter did a cost benefit analysis and recommend the move to cheaper steel cases and hardware.

In reality for audio gear does it really matter....?
 
I know well what you say. I worked for Hughes Aircraft in the mid-70s for 15 years. Radar Systems Group in Fullerton and Space and Comm in El Segundo. These are stainless screws and lock washers. These are steel.. proved by a magnet :) I guess the bean counters won by the late 70s
 
For the 500, a stock aluminum cased TO-3 SJ2501 Motorola. The hardware is aluminum, including the split/spring washers. If you look close, both screw tips are stripped or stripping....

Upside of aluminum is that it has higher conductivity.... by a lot than Stainless Steel.... Next time I am in the 500, I just might replace the steel screws I used with new Aluminum ones.... If I can find them.... Then again.... It simply might not matter....

Maybe solid copper screws....Silver any one? :)

http://www.tibtech.com/conductivity.php

I did not realize how much better a conductor Al is compared to SS..... SS actually sucks in comparison....

IMG_2454.JPG
 
Last edited:
According to the chart, all we need are brass bolts :) Nice compromise from SS and AL.. I wonder what happens to brass under repeated heat/cooling..
 
Also, comparing SS to a Tin/Lead mix ( Solder ) .... SS sucks.....

I am putting a shopping list together for my 500...and been looking online for sources of copper, brass and AL screws. This is not something that I would pull apart my 500 for just this.... But every year between Christmas and New Years... I pull my main system apart ( for some reason or another ) and do some upgrades...summer time is for cars/cycles/jetski.... 10 months and counting.... Maybe Christmas comes early?

The 500 has a lot of nut/bolts that are part of the circuitry....with 24 outputs Xters on the heat sink, a lot just there and more elsewhere... So being a 100% nerd in this post has led to some place totally unexpected, a learning exercise for me and some possible tweaks for my 500....

Hmmmmm....I wonder if this tweak will matter.... ? Always looking for a new tweak....

You got to love this hobby !!!!

johnk
 
Last edited:
Ok I just convinced myself to replace steel screws with copper....

Steel is about 40 times more resistive than copper....

That means a steel screw that is 1 inch long appears to be a 40 inches long copper screw in a circuit....

Or a 1 inch long copper screw is equivalent to a .025 inch steel screw....

Or it's like taking your 10 foot copper speaker cables.... And replacing them with 400 foot spreaker cables.... Kind of...

I just talked myself into giving this a try....
 
jstang said:
That means a steel screw that is 1 inch long appears to be a 40 inches long copper screw in a circuit....
Click to expand...

But this situation is reversed when the copper or aluminium screw oxidises, yes?

That's why gold is used for contacts, it isn't the best conductor, but it is resistant to oxidising.
 
Last edited:
At work, we often use a dielectric inhibitor when mixing up metals in electrical connections, and this is always copper-to-Al.
None needed with copper-to-copper or Al to al, obviously.
I wonder if SS is somehow not susceptible to this type of electrolysis, since no one has brought this up for the many years\thousands of units that have been upgrade\repaired. I have no idea on that, I'll leave this to you smart guys. :)

I just checked, my 2270 on the bench has no washers and the bolts only slightly magnetic.
Being as SS can be magnetic or not, I'm not sure if I have SS or Al bolts. I'm going to say SS.

EDIT: Whew, this is more than I wanted to know about magnetic SS.
https://www.scientificamerican.com/article/why-dont-magnets-work-on/
 
Well if you look in the pic of the stock 45 year old Xter and screws I posted... That shows exactly that issue, as the screws were AL and the buss they screwed into is steel.

Did they strip or did they erode from electrolysis after 40 years? I would be more concerned with Electrolysis than corrosion.... I think.....

I usually use a silver or copper paste on electrical joints like that to improve conductivity of the connection.

So will silver paste slow or speed the electrolysis process... I am not sure on that....

Does electrolysis occur in a solder joint? Of two dissimilar metals, like a copper wire being soldered to a steel post.

Any Metallurgist out there?

And I am not using solid gold screws.... :) or Gold plated copper screws.... Unless you supply them.... :D

Copper screws is as far as this Nerd is going.....

Hyperion said:
But this situation is reversed when the copper or aluminium screw oxidises, yes?

That's why gold is used for contacts, it isn't the best conductor, but it is resistant to oxidising.
Click to expand...
 
So another way looking at this... Is the increase in the Screws resistance is the same as adding to the emitter resistor.... for the given xter. The difference is that the added resistance is between the collector and the power supply.

In many NEW high end units.... You find copper or copper plated screws doing a variety of things.... Useful tweak ? or Marketing ?

Will copper screws erode faster or slow than the stock AL screws did.... ? I am not to worried about 40 years from now. I think copper holds up better, this is the reason AL has issues in home wiring and copper is mainly used.

I am going to give a spin...at some point.
 
Last edited:
Ya, you are correct - Alum wiring actually against code here in Iowa in mobile homes (it's been years and years since I read a code book, I assume it's still in place) - but it was more the loosening of the wire\lugs due to the heating\cooling cycles rather than electrolysis.

I think it's a good idea to change to copper if it's carrying a signal\voltage - SS is certainly inferior. Yup, good idea, especially when so many like the 500.
 
Seemingly copper screws are very rare.... Aluminum and Brass/copper screws are commonly available.

Ok step one is to move away from Steel screws on the main Filter caps, 4 caps - 8 screws.... Relatively easy to get at on the 500. There are 8 total. I ordered Al and Brass/copper. Not sure of the make up of brass/copper.... This one can be done as soon as the screws arrive. About a 90 min or less task. Thinking of using Al for the caps to reduce the electrolysis in the female part of the cap, as it is aluminum.

Removing the steel screws for the transistors is going to take more planning.... They are buried deep in the 500 and takes nearly a full day to get to, replace and test afterwards. Aluminum screws of the correct size are easy to come by, but I really need to plan this swap as the 500 is such a complex mechanical beast... Like mentioned, 24 Xters on the heat sink x2 is 48 screws. All are candidates.... Thinking of Copper/Bass....

I am still confused on the brass/copper screws.... What is the resistance of a "brass/copper" mix? Copper or aluminum is well documented. So is brass, but brass/copper is a bit confusing.... I guess "brass/copper" has a lower resistance than just brass.... ? Brass is made from copper & zinc... So when a screw is said to be Brass/copper... Does it have a higher copper content? And lower resistance than brass? Brass is better than SS....but not nearly as good as copper or AL.

NEED A METALLURGIST CALL OUT..... Know any? :)

Done for now till the filter cap screws arrive....
 
Last edited:
Just measured ohms of a Brass #6-32 x 3/4" screw vs an aluminum #6-32 x 3/4" screw using a meter capable of .00 measurements....

This is a typical US size used to hold down TO-3 xters. Or metric....

The AL screw measured .00 ohm , the Brass screw measured .02 ohm.

And SS screw of same size was .03 ohm.

Guess what .... a Large Main Filter cap's ESR is .006 Ohm .... So does lowering the resistance to the cap from the power Xters matter...? I am guessing yes.... but will know more when I upgrade from SS to AL....

For what that is worth.... is it significant? Only your hair dresser knows for sure....
 
Last edited:
There is always a next round of tweaks :idea:..... ALWAYS.... :smoke:

And .... Shavings make pile.... :banana:

I could not find silver screws. Although I could make them.... :D
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom