The ultimate DIY? A Stax SRM-T2!

[audiostar]

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Edited January 19, 2022 by audiostar

[Pars]

Fixed

Edited January 17, 2022 by Pars

[JoaMat]

22 hours ago, Kerry said:

A nice benefit of the modules is that you can set them to 740v before you install them in the amp. 

I’m glad everything is up and running again. 

Thank you.

Eventually I found it, among a lot of other stuff. A test board for the battery module. I probably did it in spring 2020.

Left heat sink has FJPF2145 (org. T2 it's 2SC3675) and right has 10M90S current sink set to 5 mA. Just find +250V and -560V and you are ready to go.

 

[chinsettawong]

1 hour ago, JoaMat said:

Thank you.

Eventually I found it, among a lot of other stuff. A test board for the battery module. I probably did it in spring 2020.

Left heat sink has FJPF2145 (org. T2 it's 2SC3675) and right has 10M90S current sink set to 5 mA. Just find +250V and -560V and you are ready to go.

 

I only wish I can understand what you are making.  

[audiostar]

Anyone used the T2 with a 10k pot?

[jamesmking]

17 minutes ago, audiostar said:

Anyone used the T2 with a 10k pot?

I use the mostly modern T2 with 10K (and also the mini T2, blue hawaii and megatron)

Edited January 23, 2022 by jamesmking

[audiostar]

Nice James, thanks!
Will put a 10k TKD 4CP-2511 in my original T2 and see how it goes.

[audiostar]

Made a mezzanine adapter board for the TKD 4CP-25xx pot on the original DIY T2 board from Kevin. Precisely adjusted the hight of the pot to board prior soldering. Worked out  perfectly. 

[JoaMat]

Learned how to engrave with my milling machine today.

 

It's an original Kevin Gilmore et. Al. DIY T2 amplifier with original parts.

[Rinat]

I've noticed that in later versions of the PSU board resistors R1, R2, R63, R16-17 and R64 have been changed from 400k to 300k. 

I wonder about the reason. 300k resistors would be hot: (475^2)*2/600000 is about 0.75W or 0.37W for every 0.5W-rated resistor. 

Who tried 300k or 400k ? 

[Rinat]

I've soldered 400k resistors in final.... 

The first T2 PSU works now. I've tested all the channels. 

http://ixbt.photo/photo/406668/17916TMfujOMyVu/Hgj7GE8yHX/1502281.jpg

Voltages: 

+250 -> +250

+500 ->+502 

-500 -> -502 

- 560 -> -563 

- 260 -> - 263 

 

I've also checked its transiend characteristic by loading it with an active load with a meander current from 5 to 40 mA and back. So there were changes in voltages  up to 15-20 mV for +-500v and up to 10 mV for +250 and -260v. 

 

Edited July 25, 2022 by Rinat

[Rinat]

The peculliarities of this assembly: 

1. I've changed diodes to shottky ones with a low leakage current:  IDH05G120C5XKSA1. Works well. 

2. I've used more presicion resistors for voltage dividers. That is why I've used 2 resistors instead of one sometimes - I prefer to use 2 presicion resistors intead of 1 usual xicon if there is no required value in a shop. This is also a cause of 502 voltages in +- 500 line: i've used a pair 271k + 221k instead of 490k resistor. And 120k + 120k for 240k and 145+145 for 290k. All the mentioned resistors are +-0.1% and less then 25 ppm. 

3. most HV parts are slightly raised above the board. 

4. I've decided not to solder the Low Bias part.

5. I use UF4007 instead of 1N4007 

6.  0.1 uF capacitors are X7R. I don't like ceramic capacitors, but there are no alternatives with a suitable size (. At least I use 100V instead of 50V. It lowers capacitance changes with applied voltage. 

Edited July 25, 2022 by Rinat

[Kerry]

Congrats!

[Rinat]

I also think that the short-term changes in voltages(with fast changes in current consumption) could be caused by the high(500k) resistance between 2SC3675(Q5) and FQP8N80C(Q4), which has a large Ciss (up to 2050 pf). It gives us a time constant up to 1.05 ms, which is not perfect. At least the next PSU, which I am going to make, will be done according to Jamesking's scheme. I like it more, and it would be interesting to compare. 

Edited July 25, 2022 by Rinat

[Mach3]

 

On 8/12/2010 at 11:12 AM, kevin gilmore said:

I'm pretty sure its a 1.5 amp slow blow. (for 110 vac) But it might be a 2 amp. Too lazy to go and look.

Definitely not more than 2 amps.

 

updated schematics with a couple of resistors labeled as to power, and default of .5 watt added.

 

I will have to look tomorrow on the fuse... Its never blown the fuse yet. Not even with 24 hours of CJ.

 

On 10/17/2016 at 7:12 PM, hfhimeka said:

Today, my DIY T2 has successfully come to life!  After a year on and off working on this amp on my kitchen table, I was able to power up today and get music playing.

All 4 batteries are sitting around 743V.  The +/- voltages for each channel are surprisingly well balanced, and both L and R sit about +10V offset at power-on and gradually get down to about 2-4V offset at steady state.  I measured the heatsink temperature -- looks like it's steady at 124F/51C after about 3 hours continuous burn-in.

A shoutout to GeorgeP for enabling this build--one of my good buddies helped me reached out to you about a year ago for the case/amp board/torroid set.

Thanks KG, Spritzer, and everyone else who posted all the useful information on every aspect of the amp on this thread.  I learned a lot through the process of building this amp!

One interesting thing I found while testing the PSU was that when I had both HV toroids hooked up and powered, the combined inrush blew through my 3.15A slow blow fuse (at 120VAC from the wall).  I take it that the inrush of the 2x HV toroids (at least on my toroids) are pulling closer, but not quite, to 4A, since I was able to power up one HV toroid with a 2A fuse that I had left over.  I have a 5A slow blow in there now, and so far no issues!

-Kuen

What is the correct value for the fuse in the DIY T2, Kevin stated shouldn't be no more than 2A.

However in a much more recent post, Kuen used a 5A slow blow fuse.

I'm using the same amp as Kuen, built by George.

The amp I'm using was from US with operating voltage set to 120V with a 4A slow blow fuse.

I've change the operating voltage to 240V (I'm in Australia) using the same fuse.

After turning on the unit for about 40 seconds, I see the tubes warming up.

Then the power went off, no pops, not burnt silicon smell, just a blown fuse.

Any advice would be much appreciated on what fuse to use.

I've got a bunch of 4, 5 & 6.3 amp fuse, just not 2 amp fuse.

I'm too paranoid to use any of the 4, 5 & 6.3 amp fuse.

Edited August 6, 2022 by Mach3

[jamesmking]

8 hours ago, Mach3 said:

 

 

What is the correct value for the fuse in the DIY T2, Kevin stated shouldn't be no more than 2A.

However in a much more recent post, Kuen used a 5A slow blow fuse.

I'm using the same amp as Kuen, built by George.

The amp I'm using was from US with operating voltage set to 120V with a 4A slow blow fuse.

I've change the operating voltage to 240V (I'm in Australia) using the same fuse.

After turning on the unit for about 40 seconds, I see the tubes warming up.

Then the power went off, no pops, not burnt silicon smell, just a blown fuse.

Any advice would be much appreciated on what fuse to use.

I've got a bunch of 4, 5 & 6.3 amp fuse, just not 2 amp fuse.

I'm too paranoid to use any of the 4, 5 & 6.3 amp fuse.

normally if you go from 120V to 240V you half the current draw power = current * voltage so you may have a problem. Assuming the amp did not blow fuses when set to 120V the same value fuse should not blow at 240V...

fuses can weaken over time and they do vary considerably. EEV blog on you tube did some interesting experiments and found the fuses ratings to be at best a guestimate. With large variations in the fail current for fuses from the same batch.

There are multiple versions of the DIY T2 and the choice of valves effects power consumption a little.

My T2 consumes about 205W  once warmed up (mostly modern T2 with tung-sol el34 and genalex 6922, kghssv psu).

there is a high voltage delay built in to allow the tubes some warm up before applying high voltages. When the high voltage psu switches on it initially has to fill the filter caps and this makes short duration current surge of more than 4A. Assuming there is no short circuit in your high voltage rails and you have not wired up your transformer incorrectly, its this initial charge that's blown your fuse. I am currently running 5A slow and that been fine for many months. 4A slow blow might be ok too. Having said that I always specify my transformers with resettable thermal fuses built in for a bit of extra protection.

 

 

Edited August 6, 2022 by jamesmking

[Kerry]

Mine also run at about 205W.  I've been using T3.15A 250V slow blow fuses in the US and I drop that down to T2A for 220VAC or higher.

I think these values are pretty reliable.

[Kerry]

If you're having issues with a 4 amp fuse at 240VAC you may have something wrong.  Make sure it is a slow blow fuse.  They start with a T in front of the of the value (i.e. T2A @ 250V).

[Mach3]

@jamesmking The amp been sitting gathering dusk for a while over 12 month up to 24 month. All tube been replaced with new quad matched one. Maybe the initial draw is too much.

Thanks @Kerry for clarifying what type of fuse to use, I'll replace the fuse with a new one and see how it goes. If it doesn't blow I'll replace it with a 2A fuse. 

[Rinat]

Preparing an old style active battery with LEDs. I've decided to make separate boards to test them separately from the main amplifier. 

Small changes in the AB:

1. replaced 2SC3381 with HN4C51J - I've measured them and they are very good dual bjts with very close halves.

2. replaced 2SA1486 with 2SA1413. The same transistor with different case. Power dissipation here is close to zero, so I decided to leave 1486 for hotter places 🙂   

3. 2SK246 -> 2SK208. The similar situation here with the same transistor in a different package. 

4. LEDs are LTL-4221NLC  

 

Edited August 7, 2022 by Rinat

[Rinat]

I've made a simple stand, thanks to Kerry, and all ABs have passed all tests, dropping now silently 740 volts as it shoud be 🙂

Edited August 8, 2022 by Rinat

[audiostar]

5 hours ago, Rinat said:

I've made a simple stand, thanks to Kerry, and all ABs have passed all tests, dropping now silently 740 volts as it shoud 🙂

More pics, please 🙂 Looks awesome! 

Btw, any special reason you did use SMD resistors for R12, R13? 

Did you use the 2SK208-Y(TE85L,F) or the 2SK208-R(TE85L,F)

 

Edited August 7, 2022 by audiostar

[Rinat]

19 hours ago, audiostar said:

More pics, please 🙂 Looks awesome! 

I promise to make more photos when my AB test stand will look better. And thanks for your words! 

It will be soon. 

19 hours ago, audiostar said:

Did you use the 2SK208-Y(TE85L,F) or the 2SK208-R(TE85L,F)

I use 2SK208-GR. It is the same as 2SK246-GR, of cource except the thermal parameters. 

19 hours ago, audiostar said:

Btw, any special reason you did use SMD resistors for R12, R13?

No, the only reason is that I already had them) 

There is no high voltage around them or high current through them. 

Edited August 8, 2022 by Rinat

[audiostar]

Thanks, Rinat!

PS: That Kester is the same that I use, really nice. 

Edited August 8, 2022 by audiostar

[Mach3]

Ok found out the reason why fuse blown. primary and secondary winding was wired incorrectly to the terminal block.

Grey and brown mixed around.

I need to replace the transformer, did a continuality test on P1 and it failed.

I tried to contact [email protected] at Toroidal Engineering Co.

But GeorgeP inform me it looks like he's close door since COVID.

Anyone got a spare one for sell?

@Kerry do you mind sharing what specs you're using with your transformer. Alternative route I get toroidy custom make one base on the correct current specs below. They made a custom one for my KGSSHV.

Kevin mention that the total of the primary winding should be 90watts, so would 0.5 amp each for P1 and P2 be enough.

P1 = 120V, (unsure of current rating)

P2 = 120V, (unsure of current rating)

S1 = 15V - 0 - 15V, 1 amp (Kevin provided these rating)

S2 = 6.3V,  5 amps (Kevin provided these rating)

S3 = 6.3V, 5 amps (Kevin provided these rating)

S4 = 6.3V, 2 amps (Kevin provided these rating)

S5 = 6.3V, 2 amps (Kevin provided these rating)

 

Edited August 9, 2022 by Mach3