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DIY mini T2 Build Thread


mwl168
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Some small changes I personally would like to see to the mini T2, based on my build style.

1. space for screw terminals for the transformer to el34 heater wires - I like to be able to remove boards easily for testing/inpsection etc without having to desolder anything.

2. more space between the 6922 heater screw terminal and the valve sockets. - its a bit tight.

3. the ground plane not connected to the screw holes for the heatsink L bracket. I like to mains earth my casework and leave the amp ground foating.

4. the screw terminal holes grouped like the blue hawaii, so I can use terminal blocks without having to cut a 2 way into a 1 way.. plus the one way can twist easily if you dont hold it when you tighten the screw.

5. a second ground screw terminal, - so I can have one connect to the psu pcbs and the other connect to the input signal ground.

6. have the 6922s at the front...  more valves visible more orange glow 🙂 

 

Edited by jamesmking
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Interesting … Enjoy it. 

I have finished soldering almost all the components of my T2 mini and I only need a few details to be able to hear it.

I think we all expect a T2 with current production components ... although I think the T2 mini will do quite well. Joachim has done a very interesting job with this amplifier.

Thinking in T2 mini, a TH version would be welcomed by many people.

PD: I have left my eyes with the f**** HN4A51J/HN4C51J 

Edited by jose
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1 hour ago, jamesmking said:

Some small changes I personally would like to see to the mini T2, based on my build style.

1. space for screw terminals for the transformer to el34 heater wires - I like to be able to remove boards easily for testing/inpsection etc without having to desolder anything.

2. more space between the 6922 heater screw terminal and the valve sockets. - its a bit tight.

3. the ground plane not connected to the screw holes for the heatsink L bracket. I like to mains earth my casework and leave the amp ground foating.

4. the screw terminal holes grouped like the blue hawaii, so I can use terminal blocks without having to cut a 2 way into a 1 way.. plus the one way can twist easily if you dont hold it when you tighten the screw.

5. a second ground screw terminal, - so I can have one connect to the psu pcbs and the other connect to the input signal ground.

6. have the 6922s at the front...  more valves visible more orange glow 🙂 

 

For 6. - can't you accomplish the same thing by flipping the left and right board? I, for one, would prefer the 6922 tubes in the back end closer to the input jacks to keep the signal path short and not having to worry about routing the signal wires away from the ac filament supply wires. 

Edited by mwl168
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12 minutes ago, mwl168 said:

For 6. - can't you accomplish the same thing but flipping the left and right board? I, for one, would prefer the 6922 tubes in the back end closer to the input jacks to keep the signal path short and not having to worry about routing the signal wires away from the ac filament supply wires. 

I did the flip 🙂 the small signal tubes are at the front but the labels on the pcbs for left and right and now wrong 🙃 I have the input wires going straight from the back to the tkd pot in the middle of the front panel and then nice short wires from the tkd to the boards inputs... heater wires route around the edge of the pcb close to the heatsinks. So far with the volume all the way up zero listenable hum.

 

Edited by jamesmking
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31 minutes ago, mwl168 said:

Once you get the top panel on you won't see the labels!

but I know the labels are now wrong, the incorrect labels may confuse the electrons and effect the sound.

1 hour ago, jose said:

Interesting … Enjoy it. 

I have finished soldering almost all the components of my T2 mini and I only need a few details to be able to hear it.

I think we all expect a T2 with current production components ... although I think the T2 mini will do quite well. Joachim has done a very interesting job with this amplifier.

Thinking in T2 mini, a TH version would be welcomed by many people.

PD: I have left my eyes with the f**** HN4A51J/HN4C51J 

Before the mini T2 I had almost zero smd experience, I built some of Kevins synchronous rectifiers and built two dummy dc loads from a design on you tube which had some smd op amps and thats it. The first mini t2 pcb took 2 days with lots of breaks and lots of losing components, I went very slowly and checked every joint with a multi meter. the second channel took half a day. I used a quick 861DW  hot air station and that helped, it has very good control over the airflow and temperature so I could experiment and get repeatable results. I still managed to send the odd diode into low earth orbit even with the airflow set to 5 out of 120! I found that having a led table lamp on my left, a fume extractor on my right, tweezers holding the component in my left hand and the quick hot air nozzle in my right hand worked for me well. Im right handed but I managed to control the component with tweezers in my left hand ok after a little practice. 

I purchased from ebay a head mounted visor magnifier https://www.ebay.co.uk/itm/Toolzone-Head-Mounted-Magnifier-2-Leds-Magnifying-Glasses-Repairs-Jewellery/133310425999?hash=item1f09ebab8f:g:NtgAAOSwp2deJYjP

The magnifier works and you get the choice of different magnification lenses, the headband is horrible - just plastic with no elastic to help tension.... so you either have it too loose or head crushingly tight. the light is crap and the handband uncomfortable, but it was cheap and made the HN4A51 soldering and board inspection a lot easier. Good luck with your build. Fingers crossed it goes as well for you s it did for me.

Edited by jamesmking
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hahaha, over time I think we have all orbited some component.

As for soldering, I still use a JBC with the finest tip and liters of liquid flux (from JBC too). For the moment I have not had the need to buy a hot air welding station although but.. who knows? :)

Ok, now seriously, It has taken me little time to weld the components. What has taken me the longest has been to study my boards and see where the changes have occurred (my boards are a primitive V.1), cut the center pin of E88CC sockets, etc. Small details that personally take me quite a while. 

I use a microscope connected by USB to the PC like this that works quite well for me.

About the improvements in the current board, I would just like to add connection blocks for wiring. Especially for the voltage.

 

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Here is a picture of my third mini T2.

BZ8A0297.thumb.JPG.e341a56e836873c5a0f4d1153cf445d9.JPG

Area for heat sink bracket screw holes cut away. Board now 160mm x 80mm and transistors mounted direct to heat sink. Inner dimension of case is 200mm x 161mm.

This is the way I’ve built my amplifiers for some years now. There simply is no room for terminal blocks – will only make things more complicated for me. The real thing - DIY T2 has no tblocks either (except for output to Stax connector).

 


 

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hahaha, over time I think we have all orbited some component.

As for soldering, I still use a JBC with the finest tip and liters of liquid flux (from JBC too). For the moment I have not had the need to buy a hot air welding station although but.. who knows? [emoji4]

Ok, now seriously, It has taken me little time to weld the components. What has taken me the longest has been to study my boards and see where the changes have occurred (my boards are a primitive V.1), cut the center pin of E88CC sockets, etc. Small details that personally take me quite a while. 

I use a microscope connected by USB to the PC like this that works quite well for me.
About the improvements in the current board, I would just like to add connection blocks for wiring. Especially for the voltage.
 

Damn, I might have to get something like that. I was trying to touch up a 100 pin uProcessor and am having a hard time telling what I am doing with my Optivisor.


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Pars, for $ 40 that gossip is worth it:

Central leg of HN4A51J a second after solder.

spacer.png

OPA197

spacer.png

 

Edit. Since I did my F5HA with SMD I´m use this JBC Flux It is probably not the best in the world but it works for me.

 

spacer.png

 

 

 

Edited by jose
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Since I don't have a laptop (other than my work one) readily available, or a computer down in my workshop, I'm wondering if something like these might work better for me?

https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=600X-8-LED-USB-Portable-Digital-Microscope-4-3-LCD-Screen-Tool-Zoom&_sacat=12576&LH_TitleDesc=0&_osacat=12576&_odkw=8-LED-USB-Portable-Digital-Microscope-4-3-LCD-Screen-Tool-Zoom

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In my work, one of our field technicians uses a similar model. As far as I know, in an environment like hospitals (with different types of lighting) the screen has problems with light/reflections but in a "controlled" room like our workshop it work nice.

Now, keep in mind that the screen size and resolution is not the same as the one I use.

 

Edited by jose
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838073985_tubesidev_23.thumb.JPG.231b13c87b5e60b7a7a1ef923950476e.JPG      782189479_compsidev_23.thumb.JPG.062209741816495845ca540700158882.JPG
mini T2 v.23.

Changes from v.22

  • Ground plane at area for brackets removed.
  • Silk screen lines 20mm from long side edges, cut here if you want transistors mounted direct on heat sinks. Then you also have to run wires for +B traces just been cut. Be careful you are now close to other traces - only for DIYers.

Regarding wishes for tblocks I want to quote myself (from a private conversation oct. 2018) “I haven’t used them at all with amplifiers and I have never missed them. Advantages are: - you can route the wire to the spot where it’s wanted, – the connection is much safer than with tblock, - saves space, – with a desolder gun or a solder iron they are easy and fast to “disconnect”. This also what Kevin did with his DIY T2 except for the outputs to earphone. With power supplies I use tblocks, then I find them convenient. Bottom line - IMO – tblocks destroys a layout.”

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Mini T2 Switch off thump.

I have found that when switching off the mini t2 (golden reference LV and HV supplies) I get a thump on both channels around 3 to 4 seconds after pressing the off switch. I get no thump on switch on using a 45 second delayed HV so I guessed the LV was dropping faster than the HV at switch off.  This was confirmed with a multimeter. Compared to the blue hawaii, the mini t2 drains the HV caps at a slower rate but drains the LV caps faster. I solved the switch off thump by replacing the standard 4700uF caps in the Lv supply with 22000uF. This provides significantly longer LV voltage on switch off and stops the thump. I used 30mm diameter Nichicon 22000uF 35V caps which just fit in place of the 50V 4700uF caps. I suspect 15000uF would probably work to.

regards and happy mini t2ing

Edited by jamesmking
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Folks with DIY T2 are used to “switch off thump”. I don’t know if anyone have solved the issue with the real thing.

 

I use a T2 PSU with my mini T2 and when switching off the sound just dies out nicely without any thump. T2 PSU has much less capacitors than later GR supplies which probably explains the no thump.

 

Glad you solved the switch off thump so nicely and easy.

Edited by JoaMat
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I’ve got questions about using +/-450V supplies with mini T2. It would probably work alright, I can’t see why it wouldn’t. If using a drop down resistor for +220V there is a Vishay 24.9k/3W that probably will do (haven’t tested it - maybe I should or someone else).

 

One other request is the location of stand of holes. Attached are templates for left and right boards - imperial and metric. I had to print them 100.4% to get scale 1:1. They don’t look nice but that is what I managed to do in Proteus.

 

holes mini T2 Right v.23.PDF     holes mini T2 Left v.23.PDF

 

mm holes mini T2 Right v.23.PDF  mm holes mini T2 Left v.23.PDF

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58 minutes ago, JoaMat said:

I’ve got questions about using +/-450V supplies with mini T2. It would probably work alright, I can’t see why it wouldn’t. If using a drop down resistor for +220V there is a Vishay 24.9k/3W that probably will do (haven’t tested it - maybe I should or someone else).

 

I hope to answer these questions shortly :rolleyes: 

My T2 mini will run with 450v, -450v and 220v (by drop resistor). Cross my fingers

About the question of shutdown. Isn't it better to disconnect the headset before turning off the amp?

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On ‎3‎/‎6‎/‎2020 at 12:17 PM, JoaMat said:

Silk screen lines 20mm from long side edges, cut here if you want transistors mounted direct on heat sinks

 

Here is a PCB with unnecessary area. A big metal saw and it’s fixed in a couple of minutes. :mikey2:
BZ8A0299.thumb.JPG.9099f6df2115e494570448ac2c390ade.JPG

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Today’s exercise.
IMG_0289.thumb.JPG.777b18af9ed5de1cfab6decef9eb83c0.JPG  IMG_0290.thumb.JPG.53292e0602679899450645a9f757b275.JPG

Milled a double sided board and populated it. Now I know it’s fairly easy to solder this by hand. If you can solder a mini T2 board the GRHVxxx boards shouldn’t be much of a problem. Besides it’s funny.

This board is essential the same as Kerry’s except no enable and a trimmer to adjust output voltage.

Thanks for those mini boards Kerry.

 

Edited by JoaMat
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Now it’s tomorrow and it turned out to be long day. My work flow nowadays is first schematic and then board layout. The idea is that I can’t make a board that doesn’t follow the schematic and in the end minimize board errors. And it actually reduced my errors to almost zero… but an error in schematic will guarantee a board that is schematically error free but also something that doesn’t work properly.

Two errors in schematic are now corrected and the little thing works like charm. :)  By the way - yesterday was a Friday 13th, wasn’t it?

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Milled a new “corrected” board on Sunday. When populated and ready for test the bloody thing worked fine for a few seconds than it started to decrease voltage slowly down to 230 volt or so. I started to change component by component and when just a few unchanged I replaced the dn2540 and issue solved, phuuu.

 

Anyhow. Now the regulator seems to work alright, okey just 10 – 12 mA of load. With trimmer (200R) there is a range of 5V at 400V. Picture shows 400.0V and after 20 minutes the meter in “minmax” says average 400.0V within -0.0/+0.1.
IMG_0455.thumb.JPG.3998101a4a085d7c5aabf6ddeeeb884f.JPG

 

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A few years ago I bought a Weller hot air station WTHA 1. It was my first hot air station and I thought it was a good station. It was quite expensive so it had to be good! Suddenly the display showed “Error 3” and nothing more happened. No guarantee left and I couldn’t remember from whom I bought that crap from. After some investigation I bought a Quick 861DW. Now I’ve used the Quick for a while and I’m very happy with it and it costs a third of the Weller - and ten times better.

 

I use a Weller!! solder station for smd soldering and have no intention to change that. But when working with the Quick hot air station the last days I tried to solder components with the Quick and it did work quite well.

 

So, first I thought this is a complicated way to solder smd parts..

On ‎2‎/‎14‎/‎2020 at 7:09 PM, jamesmking said:

SMD soldering was done in a three step process.

1 apply solder paste to the pads.

2. melt the solder using a hakko 888D station at 330 degree C using a fine tip until the paste has migrated to only be on the pads.

3 Hold the component with twisers onto the pads and with my other hand use a Quick 861DA hot air station using the smallest supplied nozzle with airflow setting all the way down to 5 (even then its possible to send one of the small diodes into orbit with that air flow)...  to reflow the solder onto the component.

the reason I soldered this way was,

1. I could collect any excess solder with the hakko, since I dont have an electronic solder paste dispenser... 😞 

2. I could be reasonably certain there was no solder paste left under a component.

… but I now I’ve changed my mind, well worth trying – Thanks for sharing this, James.

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