[Russellc]

The amp is running as cool as I would expect.  I am now getting distortion in the form of static in the highs.  I have some work to do.  I do have an o-scope I just need to harrass my buddy to teach me how to use it.

I'm in the same boat, but do not have the o-scope yet.....I keep telling myself to get up to speed, but I still dont have one.  Its really a necessity with amp building, I really need one and someone to show me how to use it!

Russellc

[Russellc]

Ok, some chassis building is about to begin.  I have ordered the 10.080 inch extrusion from HeatsinkUSA, 8 inches tall with 2.3 inch fins.  They appear to be thermally sufficient, but without a lot of extra capacity.  Plus, I will be using Kerafol insulators, which are said to keep the devices noticably cooler than Sil-pad or even mica and goop.  Several of the experts think this will be plenty for a standard F-5.  Once they arrive, the measurments will be sent to Westend, who will cut the aluminum panels and corner angles to fit.

The boards are stuffed, (Peter Daniels versions) using Caddock and Mills resistors.  Need to order the pots and binding posts, have just about everything else.

Russellc

[Russellc]

Once the sinks and panels are in hand, the back panel and heatsinks will be attacked first.  Holes for electrical in, fuse, rcas, binding posts will be cut, and the holes for the mosfet mounting screws, the corner pieces and top and bottom angle aluminum will be drilled and tapped.  Only the holes in the heatsink are tapped, the other holes in the angle pieces them selves are just through holes.  The only other holes to be tapped will be in the top angle piece, which will need threads for the screws that hold the top on.

More when the aluminum is in hand, where pictures will make this much more clear.

Russellc

[Russellc]

Closer now to construction, I have the HeatsinkUSA heatsinks in hand.  I would have loved to have been able to use the M&M sinks again, but they obviously have no interest in the DIYer. It would have cost 3 times the price, as opposed to just slightly more than the Heatsinkusa extrusion when I bought 4 at the time last time.  One member got an even higher quote for a group buy situation! Shoot, I could order from Conrad in Ozzy land and got them cheaper, even including the shipping from the other side of the world.  Message from M&M quite clear!

The Heatsinkusa 10.080 inch extrusion is very nice.  Base is just as thick as the M&M piece, maybe a tad thicker.  Fins are closer together, but thinner than the M&M sink's fins.  My M&M were cut 6 or 6.5 inches high, just over 12 inches long. These sinks are 10.08 inches wide, 2 inches shorter....except actually a little shorter.  There are two "studs" on the end of the sink that extend about 1/2 inch, where as the M&M sinks had fins on the end piece, no stud sticking out.  Net effect, extra inch of "no fin" area. To counter the loss,
I made these 8" high, but gains from extra height of the sink are minimal, length seems to make much more difference.  Also I will be using the Kerafol insulators which are said to transfer heat even better than mica and goop.  People who know tell me they should be fine like this.  We shall see!

Russellc

[Russellc]

 



These are the HeatSinkUSA 10.08 inch extrusion with 2inch + fins.  It is 8 inches tall.
It has been marked to position the Peter Daniels F-5 circuit board.  The pins of the Toshiba output mosfets will be bent up 90 degrees on each side, so the small light weight circuit board will be supported "dead bug" style.  Now the mosfet leads can be bent, and placed in the board's mounting holes.  Then the position for the hole that will hold the mosfet against the heatsink surface can be marked, drilled and tapped for 4-40 threads and screws.  Then a kerafol will be slipped under each mosfet, 4-40 hardware with small fender washer will hold it to the sink. Then, the legs of the mosfets can be soldered stress free.

[Russellc]

First pic shows using the punch to mark the spot where the hole is to be drilled, as well as making a point that is easy to keep the bit in.  In this case, we are drilling for 4-40 sized screws that will clamp the mosfet against the heatsink.









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The hole is slowly drilled a little at the time through a small puddle of the thread cutting oil.  Take your time, cleaning up the small pile of shavings.  another drop of oil, drill a little further, stop clean repaeat until the drill comes though.

[Russellc]

Here is the resulting hole.  Wipe away any old oil and shavings and get ready to dress this hole.  This is fairly important here, as to leave any burr around this hole can cause troublesome shorts when the stick through your pad to the back of the mosfet, which is drain.  Using this little bit, I carefully remove any burr and leave a nice bevel there.  after the tapping is done, it will be lightly touched up again.

[Russellc]

Here is the resulting beveled hole.  Next it will be tapped with the 4-40 tap, then lightly touched up again to remove any trace of burr from around the hole.




Here is the tap and die.  Nothing fancy, it just clamps in there and you twist it in.  Oil is applied to the hole and the tap, it is slowly turned until it begins to catch.  Turn it in slowly until any resistance is felt, then back out, push some of the oil down the hole, turn it back in until resistance, stop, back out some, then in again.  Always take your time and dont force anything.  As soon as it begins to bind AT ALL, back out some, then back in.  Keep pushing the oil puddle to the hole, stop clean the tap and replace the oil puddle if necessary.  Keep going, back and forth until it goes through, when it will get very easy to turn.

[Russellc]

Here's a 4-40 screw in the new threads.

[Russellc]

Here's the finished sinks, well for these two holes anyway.

Close up view:

[Russellc]

Next will be some polishing of the heatsinks face with extremely fine sandpaper.  This allows for a better junction between the sink and the back of the mosfet.  With a class A amplifier, there is lots of heat.  Without a proper junction between the mosfet and the sink, heat will not transfer properly.  The sink will measure OK, but in truth the mosfet is seriously overheating and will fail.  My last F-5 build used a considerably larger (overkill)
sink.  This one is perfectly adequate, but isnt over kill, so the mosfet to sink junction is very important.

After the polishing, they will be carefully measured and aluminum stock obtained for the front, rear and bottom panels. Then a face plate will be attached to the front of the amp.

Once panels are here and test fitted together, the rear panel will be cut for the input RCA jacks, the binding posts, the AC inlet jack, fuse and switch.  (switch may end up on the front panel.)  Then the panels will be drilled with through holes to bolt them together.  Angle aluminum will form the corners and attach the rear panel, front panel, bottom panel.  Also holes will be drilled in the sink to attach these corner aluminum pieces, and they too must be tapped.  These locations as well as the other through holes will be using 10-32 bolts, nuts and washers.

All this will be presented with pics of course.

Russellc