The ultimate DIY? A Stax SRM-T2!

[niner]

In Boston area of USA

[iwik]

I noticed the original heat sink that Kevin used had the fins running horizontally.

I know they look better this way but how much less efficient are these compared

to fins vertical. I know this was custom material from Justin, but were looks

preferred to ultimate efficiency with Justin's choice.

Thanks

les

[kevin gilmore]

custom casting of vertical heatsink that size brutally expensive.

and while it is more efficient, it is not not that much more efficient.

[luvdunhill]

They seem much more efficient to me. Ironically, the higher heat might help stability a bit as hfe rises with junction temperature and there are some places where the hfe of the transistors seem important. As KG said, surely some transistors were matched and hand-picked, but that process has been lost to the ages.

Also depends on what height you pick, obviously. You aren't bound to the same height the original used and a bit more height will allow you to center items on the panels if that's important to you.

The other factor might be finishing, raw aluminum versus powder coating (not sure how the original GB were finished)?

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[iwik]

Thanks Kevin, just wondering which way to go. Either heatsinkusa with horizontal

or locally with two joined for vertical.

[spritzer]

The other factor might be finishing, raw aluminum versus powder coating (not sure how the original GB were finished)?

 

They were anodized. 

[luvdunhill]

Ah. Doesn't help my theory then

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[kevin gilmore]

heavily anodized. no color changing here...

[shipsupt]

I got a note from LilKnight who's having some network issues... He's trying to get the chassis work finished up.  Here's what he's after:

 

"Could you check with the guys which volume pot they are using? The rk50 has 8mm diameter shaft while standard is only 6mm. I am thinking of making 6mm, so if you use the rk50, you just need a coupler, will forward you the link to that."

 

I can reply to him via email with the info.  I'm not sure how often he's been on here lately.

[kevin gilmore]

board is rk50 or dact. both work with a .25 inch coupler

[n3rdling]

Is he talking about the hole on the front panel? May as well make it 8 since the knob will cover the hole.

[nopants]

Wouldn't it require some sort of washer for any pot that isn't the rk50 then?

[kevin gilmore]

panel bushing for the front panel. look at the original diy pictures.

[luvdunhill]

Unless you have perfect math and tolerances, leaving some extra room in the panel bearing might be a good idea. You can go a bit bigger and the nut (not to mention the knob) will cover it up.

[iwik]

I am about ready to do some chassis work. Wondering about the L bracket for the transistors.

Kevin used 3mm on his and I see LIL Knight is going to use 4mm. Is there any real advantage

in using 4. Just checking before purchasing material.

Thanks

Les

[kevin gilmore]

i used .125 inch material. which is standard in the usa. thicker should work if you machine a bit more

off the transistor edge.

[luvdunhill]

There is also an aesthetic concern. I like the legs to come straight off the devices and then have a single 90 degree bend. Going thicker means you won't have enough lead material to do this. You will also have to bend at the base of the transistor, if I recall. The concern doing this is arcing from the lead to the bracket edge if this angle becomes significant. You can avoid this by machining more off the edge, but then you don't get as good heat transfer between the device and the bracket as part of the case slug is exposed to free air.

Edited March 24, 2014 by luvdunhill

[iwik]

Thanks all,

Can get .125" angle ally so will go with that.

Can someone point me to the latest Schematic for the Amp.

Kevin sent me the Power Supply but are unsure which amp ones

I have come across in the thread are current.

Les

[kevin gilmore]

schematic has not changed in forever

http://gilmore.chem.northwestern.edu/t2schem.pdf

[iwik]

Thanks

Les

[iwik]

Hi,

What is the general consensus for the torque value for the To220 and To126.

Any good links to Torque adjustable drivers that a single one will handle.

Les

[justin]

Tohnichi 12LTD-A (2 to 12lb-in) will cover the full range of torque options except the M3 PEEK screws are supposed to be tightened to 1.3lb-in and for that you'd need the 6LTD-A (1 to 6lb-in).  There are more part #s too that have the torque in metric, might be easier to find depending on where you live. Check both options if you're trying to find a used one.

 

i think for TO-220 you should use 5 to 8lb-in depending on the spec of any insulating washers or spring/conical lock washers, assuming a metal screw, for plastic or ceramic screws you will have to go much lower.

 

not sure what it is for TO-126

 

 

I picked these up for $75 total on ebay. the gold ones are Tohnichi 12LTD-A and 6LTD-A. The other one im not even sure how to adjust it but it feels nice. Seems designed for high volume assembly.

 

edit: actually the one on the right isnt the 6LTD-A it's a RTD50Z (15-50oz). I have a 6LTD-A (not pictured) but it's in worse condition and is missing the locking ring. still works though

Edited March 26, 2014 by justin

[mortal_fiend]

Have sent designs in looking for quotes on the PCBs.  As no purchases have been yet made, how much more difficult would it be to go the dual power-supply route (aside from the obvious factor of another chassis/board to make)?  My understanding is that it should be fairly straightforward as it was designed said way.  I have a decent amount of DIY experience (b22 most recently) and the additional chassis is not an issue (plenty of machinery here on my end).

[iwik]

Thanks Justin,

Really helped seeing yours. Came across plenty on ebay but to reset them you needed a gauge.

Anyway I did see a few but unfortunately a lot wont ship International. So will just

wait till I find one that will.

Les

[iwik]

Is there significant advantage using Teflon Sockets over the Ceramic ones. Supplier shipped me 9 pin ceramics

instead of Teflon. Is it worth exchanging them.

Thanks

Les