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The ultimate DIY? A Stax SRM-T2!


spritzer
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  • 2 weeks later...

Hi All

 

 

Thanks, but Dale rn60 would have some noise problem like prp's?

My experience:

 

I had a LOT of trouble with noise, and replace a lot of parts. Changing my Shinkohs to Xicons helped a bit, but the trouble/noise came back. This made me think, that Xicons were better because of the 50ppm, but that 50ppm is still way too high. So i re-replaced some of the resistors with only small benifit.

 

Finally the one thing that did the job was replacing the 10K pots in the four battery-sections, with a super-low ppm resistor:

5ppm (!!) in the series ptf56 from vishay,

that had the same value as what i adjusted the 10K-pot to (6K in my case). Then i could do all the final tuning with the 2K pot.

 

THIS thing made the amp TOTALLY stable, and dead silent.

So for 6 month i have enjoy'd the fantastic sound from this beast of an amp   :dance:

 

 

Happy new year to you all!!

 

Peter

Edited by pedefede
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I recently bought a  B&K 501A curve tracer, was incredibly cheap on eBay.  Seems to work fine.  Anybody have any experience with these?  

 

I've also got one of those little Chinese transistor tester gizmos too, that gives you breakdown voltage and a few other parameters. That seems sufficient to screen out fakes, but now with a curve tracer I should be able to match devices decently when that's needed.

 

Still haven't freed up enough workshop space to build my T2.  I might be deaf by the time I finally get around to it......

 

Also got one of those Tektronix differential HV probe gizmos, too.  Girding up.....

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ok, testing the fake looking 2SA1486 i just got.  they came packaged in tubes.  

 

The back of the parts look just like the real ones

The front is very clean but doesnt use the NEC font

 

The part feels lighter than the real ones.  The leads are much thinner, and are brightly tinned on the 'fake' ones.

 

Now for the testing....

Voltage - 685 to 715.  just like the real ones

HFe - 70 to 80.  real ones - 110 to 115.  both are labeled "K" grade which is good for 60 to 120 HFe.

 

so very confused right now

Edited by justin
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John beat me to it!

 

I really feel for Justin and others that need to source these oft faked parts in small commercial quantities.

The whole situation blows.

 

i can order a couple thousand of legit ones from Arrow -- Renesas branded, which should be identical to the NEc part.  though they tried and tried, they were unable to ever tell me the HFe grade of the part.  

 

this is just less $$.  they test good for 700V, they have HFe in the proper range, so, i have no reason to believe these are fake.  my concern would be that the picture they send me doesnt look exactly like the 200 that they shipped to me.  

 

Could someone fake a transistor and still have 700V and proper HFe?  i guess its possible.  i'll see if KG can do some further testing

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I think that a curve tracer or a specifically designed test circuit

is the way to go. What i am really looking for is a 500 series tektronix

curve tracer, i will ask around in a few hours. If the curves are close

and the BC capacitance is right, then even if they are fakes, they are

usable. But the ROHM parts should be an exact substitute except they are

surface mount only.

The problem with the cheap curve tracers is that they don't go up to

the high voltages.

I put in a bid on a tek 577 thats local to me, so everyone stay away

and we will all benefit.

Edited by kevin gilmore
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  • 2 weeks later...

the joys of 35 year old gear with dirty switches...

Finally got the higher voltage range working, but did

not take pictures. Never did get the trace blanking working.

50 volts per division horizontal, .5ma per division vertical

20 ua base current per step. Horizontal and vertical flipped

so it looks like a npn.

The first 3 are known real

http://gilmore.chem.northwestern.edu/dsc_0316.jpg

http://gilmore.chem.northwestern.edu/dsc_0317.jpg

http://gilmore.chem.northwestern.edu/dsc_0318.jpg

the next 3 are ???

http://gilmore.chem.northwestern.edu/dsc_0319.jpg

http://gilmore.chem.northwestern.edu/dsc_0320.jpg

http://gilmore.chem.northwestern.edu/dsc_0321.jpg

So other than beta being lower, sure look to be the real thing.

High voltage tests, all of them break down between 650 and 700v

will measure capacitance later.

Edited by kevin gilmore
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  • 2 weeks later...

The old B&K 501A  only goes up to 100v on the collector / drain  so not of use in sorting these out.

 

The little DY294 tester goes up to 1500v for it's breakdown test, so with that unit you can see if the breakdown voltage is where it should be; this is at least a good start for the DIY user, but for someone like Justin, or Kevin, it doesn't go far enough.

 

 

DY294

dy294.jpg

Edited by Milosz
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  • 3 weeks later...

Justin, any news on the 1486s?

 

yeah, i got 5,000 of them.  they test good for about 700V, or at least most of them do.  a few percent do not.  the quality of the leads is poor.  They also test full of lead, thanks to Kevin Gilmore's testing.  not that i would care, but the box says Pb-Free which makes the whole thing suspect.

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the nitric acid blank (i used the cheap stuff)

http://gilmore.chem.northwestern.edu/blanknitric.jpg

the nitric acid blank over the sample

http://gilmore.chem.northwestern.edu/full.jpg

the expanded sample alone actually saturated the detector

http://gilmore.chem.northwestern.edu/transistor.jpg

Its so nice to have an ICPMS laying around :D

Edited by kevin gilmore
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