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Why pull and redo power transistors on the heatsink

jstang said:
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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....
Click to expand...

Well, yeah, that's at the heart of just about every debate there is in audio. From a technical measurement perspective many, many things cause a change in what can be measured with sensitive-enough instruments. Where that changes from mere numbers on a gauge to the plausibility of causing an audible difference is the real point, to me any way. On the other hand many don't really care; some sort of change is good enough to pursue it, regardless.

BTW, the output transistor mounting screws in my recently-acquired H/K PM650 appear to be some sort of copper-ish looking metal.

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Tweaking is all part of this great hobby....

Copper screws, yum.... Only problem with them in that application is that the plastic cases are not Current carrying like they would be for TO-3 style Xters... The collectors on the plastic Xters are soldered into the circuit VS the TO-3 collectors use the screws, washers and sockets.... Honestly, I like solder over just screws....

So looks like the copper screws is marketing only in that H/K.... or maybe the intention is to improve thermal conductivity, which copper is also better at than steal....

Also, interesting in that pic.... Seems some one put dielectric thermal compound under a grounding lug .... Please tell me I am wrong on that one.... :D

My aluminum screws to replace SS for the filter caps are in the mail.... One step at a time. Next will be new aluminum screws to the replace the SS for the TO-3s.

My plan will be to perform a voltage drop measurement with my hand held scope between the TO-3 case and the Power Rails....this is an ideal application for the hand held scope - floating ground. I want to measure the voltage drop during high load.... With SS screws and AL screws... On other units I have improved connectivity between Outputs and Power Supply before via various tweaks ( heavier gauges ) which provides improved performance.

Might start a search for aluminum case TO-3 power xters, but think those are long gone.... seems we are stuck with Steel cases.

jk


whoaru99 said:
Well, yeah, that's at the heart of just about every debate there is in audio. From a technical measurement perspective many, many things cause a change in what can be measured with sensitive-enough instruments. Where that changes from mere numbers on a gauge to the plausibility of causing an audible difference is the real point, to me any way. On the other hand many don't really care; some sort of change is good enough to pursue it, regardless.

BTW, the output transistor mounting screws in my recently-acquired H/K PM650 appear to be some sort of copper-ish looking metal.

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As we are nitpicking about this stuff right now, I would like to add something to the confusion:

All those Alu Motorola TO3 transistor casings all have the B and E stamped on the bottom of the transistor and the edges of them more or less sticks out a bit on most of the transistors.
Conclusion: The alu cases are less flat than the steel cases so they require more white poop.
 
https://en.wikipedia.org/wiki/2N3055

Look at the chart....

T41 case is aluminum.... Hmmmmm... Is there hope for us that have the old Motorola based amps.... Looks like Tesla copied the old Motos...

Ebay has some of the Teslas and some NOS Motos in the AL cases....
 
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:) Feedback is breakfast of champions.... except maybe too much in amps....

Digging in to find more al cased Xters... We seem satisfied with the steel case Onsemis.... which is fine, but I am going to look a little closer. Seems Tesla created their al version for high power audio amps... Is it worth it? They seemed to think so....

One step at a time...

OnSemi has us cornered ....they cornered the market...

Seems Tesla Semi is part of OnSemi.....

NOS may be the only source for AL cased TO-3 .... once again....
 
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No conclusions here - just photos of a Sony CDP I own. Nicely built. I'm gonna say those are copper screws. Not alum case transistors, so...
Sony NS999ES 01.jpg
Sony NS99ES 01.jpg
 
Well that's pretty.... Runs cooler... Somewhat ... What's in there? Regulators?

I am not anti copper or anti aluminum.....


When copper forms a green oxide covering, it's still conductive..... While aluminum oxide is not..... That could be an edge in some applications.
 
As my avatar suggests, I like the gold plated transistors like this 2n1722 better . No problems with different metals having golden transistors, golden music and golden ears. Music from a golden era.
Get rid of 1% resistors, you need 5% tolerance color coded resistors, because otherwise there is no golden colored band on them.
Golden sleeved capacitors may help, too, as above pictures suggest.

:thumbsup:
 
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I just swapped out the Filter Cap screws on the main 500 today from Steal to Aluminum. I physically could not SAFELY measure the voltage drop across the screws...just no easy way to get at the posts coming out of the caps without risking a major MIND BENDING short...88,000uf at 80 volts, major arc welding. If you have seen the main filter mounting in the 500 you will know my hesitation. 8 of the M6 - 1 screws because of the 4 main filters.

The steel screws I removed were tight....the caps are only 2 years old and hence the metric screws. I made no other changes today.... Not an easy task...top, bottom and front of the 500 has to come off. When I swapped the caps, I considered Four Pole units, but that would have been a bear to implement on the 500.

Well I have played this game of improving conductivity between the power stages and caps before... so I kind of know what to listen for..... And yes I heard a small but noticeable improvement in definition across the freq range. Its kind of like lowering the ESR of the main caps.... Because it is the same as lowering ESR but across the entire freq range.... It also reliefs the main feedback loop of needing to make small corrections to make up for these loses in the supply voltage for the fine/small details riding on top of the large signals.

So.... I also received the 48 Aluminum #6-32 screws for the transistor mounts ( actually ordered 100 for 10$ )... I will absolutely measure the voltage drop BEFORE AND AFTER on that change , as it is easy to get physical at....

I also plan on adding a custom made bus for the collectors to the main caps. To bolster the stock wiring and power buses located behind the heat sinks... If you have worked on the 500, you know the power buses I am talking about.... I never really liked the design. And felt it was one of the few limiting factors in this amp. There is always a WEAK LINK in every design....

The transistor mounting screws and custom busses will have to wait... that will be an all day effort and its finally starting to get warm here..... :)

John
 
Hyperion said:
Another two reasons for removing, cleaning and re-applying. (presence of Silicone grease, and migration onto leads).
Click to expand...

if thermal grease migrates on into the sockets and on to the T0-3 output transistor pins, what is the typical sonic outcome?

I ask because I have an old amp with migrated thermal grease into the sockets.
 
A thing to keep in mind is what happened to me back in the mid 80s. I had had my Pioneer SX-1250 for close to 5 years. The audio tech who worked with me had suggested what this thread is about. He said I should remove, clean and re-silicone my transistors and this is what I did. I was confident that I had done a proper job. When I got home I wired it all up and turned it on and BOOOOOOOOOMMMMMMM!!!!!!! A sound as loud as a 12ga magnum and a 18" flame shot up. It appeared that one lead of one of the transistors had somehow been placed in contact with the heat sink. I had no idea of how it could have been replaced wrong, but it did. My heart was pounding like a freight train.

That SX sat in my den for 8 years. I knew I would never be able to pay to have it fixed. Some sweaty Summer day, I just decided that it was time to go. I put it out next to the trash can. I sat in the living room and was there when I saw the trash truck come up, the man picked it up and, BOOM!!!! into the hopper it went. at the same time my heart dropped to my feet. I hurt so bad, but it was over.

Do not do what I did!
 
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