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kevin gilmore

stax t8000 clone (well sorta)

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Now with left channel. The work with left channel went very smooth – no errors – like plug and play. Need a top plate, fix that tomorrow. And a matching PSU… but now I need some vacation.

IMG_0211.thumb.JPG.29a63f360d4fa3f93609b99bccab8589.JPG

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On 9/18/2018 at 2:38 AM, kevin gilmore said:

in theory with appropriate adapters or the right circuit board layout it would work. Lots more filament power. Lots more heat.

Thanks, Kevin

el156 filament current is 1.9A,  compared to el34 1.5A, increasing in filament heat/power seems to be acceptable to me...

 

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Now with top plate.

 _MG_1607.thumb.jpg.6b2e9735ac90ba2175eeacd1950fc9a9.jpg

 

Aerial view, the two holes in front of outer small tubes are for balance trimmers. Adjust balance after some time of warm up and then insert jumpers for the servos.

_MG_1608.thumb.jpg.2fc1416660ea2bb3a4d5213d950016e4.jpg

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I am very satisfied with the outcome of this build. Some background. I wanted to build an amplifier based on the T2 but simpler. There isn’t anything I’ve invented. I just copied and pasted pieces and ideas from Kevin, Kerry, Birgir et al - without asking for permission. Draw up a schematic this morning of the amplifier in the same “fashion” as DIY T2 by Kevin Gilmore. The amplifier doesn’t have R66, which is suggested by Kevin.

Be aware of errors since I did this in a rush.
schematic.thumb.jpg.de42e42af931ad31660856f6178a760c.jpg

As about the sound. I AM VERY HAPPY with her. But that’s maybe like asking me how much I love my four grandchildren.:)

Edited by JoaMat
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Have been listen to the new amplifier with EML 20B v4 tubes for a couple of days. Since 20B pinout  and heater voltage differs from EL34 I use adapters. Maybe it’s about time to make a board dedicated for the Emission Labs tubes. The tubes looks amazing and have printing on the glass. In this early stage layout the printing and the front of the tubes are facing the listener.

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I found the big tube 3D model (300b) at grabcad.com, done by Andrew Whitham, United Kingdom.

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I’m sorry, but - I will not compare my, in kitchen made, amplifier with the famous DIY T2.

One way to compare…   well, build one – it’s fun. Schematic above.

Edited by JoaMat
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16 minutes ago, JoaMat said:

 well, build one – it’s fun. Schematic above. 

I think it can be a good project for Christmas.:rolleyes:

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With JoaMat's blessing, Jose and I had the "mini T2" PCB fabricated for our use.These are proven boards - one working amp has been built. The right board has one error – one 1206 resistor got a 0805 pad but it’s possible to put the 1206 on it. 

The boards are 2mm thick, 2oz copper and right and left channel boards are mirrored (see pic.).  

There are a few remaining sets available, PM me if interested.

 

EDIT: Added schematic and BOM that JoaMat provided. The BOM uses thick film resistors, you may want to substitute with thin film resistors.

 

 

mini T2 PCB.JPG

 

BOM mini T2.xlsx

Schematic mini T2 (1).PDF

Edited by mwl168
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I’m using a modified T2 power supply. +250V reduced to +220V. +/-500V and -560V are reduced to +/-400V and -460V. +/-12V increased to +/-15V. Filaments as original.

But the -400V is not used at all with this amplifier.

Edited by JoaMat
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Hmm, so the options is to go with T2 PSU and Modified it, then use GRLV for +/-15V (additional option) ?

Edited by Whitigir

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Well, I changed the voltages as said above on a T2 PSU that is a bit different from the original. I used those lower voltages for my T2 for some time before I built mini T2 and it worked great. So if you dare to lower the voltages on your T2 PSU and remove the 7812 and 7912 and put in  the https://www.amb.org/audio/sigma78_sigma79/ set to 15 volts. Then you have an universal PSU.:)

I haven't tried AMB sigma78/79 in T2 PSU but someone has to...???

Edited by JoaMat
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2 hours ago, JoaMat said:

I haven't tried AMB sigma78/79 in T2 PSU but someone has to...???

Oh! I forgot Kerry’s micro GR - that would really be something. Link

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In a first attempt I will use my Universal PSU (GRHV +/-450v) with resistors to reduce the voltage (as in the Megatron).

I'm not sure it's the final configuration but ...

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Have a couple of these since last GB (psu for the tube ubal to bal board). Guess they would do the trick (possibly with some component updates to handle +220V) ?

GRHV 100V.jpg

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On 2/17/2019 at 6:02 AM, mwl168 said:

/snip/

EDIT: Added schematic and BOM that JoaMat provided. The BOM uses thick film resistors, you may want to substitute with thin film resistors.

/Snip/

BOM mini T2.xlsx

Schematic mini T2 (1).PDF

On a quick look over,  the Schematic mini T2 (1).PDF linked does not match the schematic Joachim posted above. In particular, the one linked shows an additional -400VDC supply is requried, That -400VDC supply isn’t needed per Joachim’s latest posts and schematic.

Wondering which version of the schematic applies to the PCBs? 

Edited by Laowei

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Ajaj!  That -400V is something from earlier schematics I worked with and I obviously forgot to remove it. The -400 V potential is created by voltage divider R53 – 56. Otherwise the schematics are identical except for that components have different coordinates (I hope, crossing fingers).

Thanks for noting it, Steve.

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