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The ultimate DIY? A Stax SRM-T2!


spritzer

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I also wanted to add a note on the 680uF capacitors. The BOM specifies a Panasonic cap that is 45mm in height, but the description says 50mm. These caps were unavailable at the time so I went with 50mm caps and they are a bit too tall. I'm going to replace them, but I wanted to make sure everyone still buying parts knows that the max height on the caps is really 45mm.

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With the 50mm caps they touch the lip on the faceplate. You're right, I was concerned about the screws going into the cap. I could cut them down, but if you accidentally put a longer screw in it seems like bad thinks could happen.

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  • 2 weeks later...

I got some questions about the tubes.

Regarding the input tubes, do they really have to be a matched quad, or just matched pairs would be fine? I have some pairs of Siemens and Telefunken CCa but most of them are matched pair, hard to get a closest quad.

Also, is there any significant difference between the xf1 and xf2, construction or SQ? I've just scored a quad of xf1, OO. Not sure how they stand up against the xf2 which are really tough to find NOS ones these days.

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No need to have a matched quad. More important to have the

halves of the input tubes matched section to section.

Build my own tubetester (out of a cheap PC-scope). Lot of fun - and it seems to work

So for testing input tubes, i deducted the following from the amp-schematic - please comment:

operating points, where i need to measure:

U2:

Vgrid = -2 V

I = 5mA

Vplate = ?? cant see

U1:

Vgrid = -1 V

I = 5mA

Vplate = 69V

What is the most important parameter? Gain/mu or transductance?

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All the boards including yours were reamed with a #74 drill bit.

The 3381's fit, but are very tight. I would not go any bigger unless

you want to solder both the top and the bottom.

U2 plate voltage about 210 volts.

My umbilicals were about 3 feet. You should be able to go to 4 feet

the only issue is with the filament voltage on the output tubes

due to increased resistance.

Edited by kevin gilmore
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Thanks Kevin, I was actually looking for the tool for another use. I didn't realize a drill bit would accomplish the same thing, until I thought more about it... I just had the word "reamer" stuck in my head I guess.

Did you stick the bit in some sort of hand tool then? I figured many chucks wouldn't down go down that low..

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Here's another option:

http://www.drillbitcity.com/catalogue/product_detail.asp?Tg=100-10W79-70

These are drill bits with 1/8" shafts. They've got lots of other sizes. Get extra... they break if just think about doing something wrong. I use them in my mill on PCBs.

EDIT: Ditto on the changed url :)

Edited by Kerry
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Here's another option:

http://www.drillbitcity.com/catalogue/product_detail.asp?Tg=100-10W79-70

These are drill bits with 1/8" shafts. They've got lots of other sizes. Get extra... they break if just think about doing something wrong. I use them in my mill on PCBs.

EDIT: Ditto on the changed url :)

aaaahh.. thanks! I like the idea of not having to use a drill press though, so we'll see if I have steady enough hands.

Thanks guys!

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I got a lot of practice using pin vises back when I played Battletech (and assembled the little Mech figurines), but it really isn't that hard to use one. Once you get the hole started it just becomes a matter of time; just try not to snap the bits too often. :P

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