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kevin gilmore

stax t8000 clone (well sorta)

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Left and right sides ready?jep.thumb.JPG.4591b96232ff170f21b11d227599f1dd.JPG

 

Seems to be some errors to fix. And wife got a new assignment - to be celebrated…
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In T2 one tube act as lower and the other tube as upper device.  Another way would be to have one tube for each side.

This adapter board changes to single tube per side.
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The T2 way makes the layout a bit more elegant then single tube per side. Else pro/cons - I have no idea… anyone?

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For a cascode stage (SRX, T2) I prefer to use one tube as the lower and one tube as the upper. The reason is that the input tube cathode sits at ground (roughly), whereas the upper tube cathode sits a a positive voltage. Most input tube types specify a maximum filament-to-cathode voltage of 100 volts max. So the potential issue if you use a dual triode tube per side is that either the lower or upper cathode filament-to-cathode voltage will exceed that maximum, leading to shortened tube life. OTOH, if you use one tube for the lower and another tube for the upper and float both filaments, you don't have that issue.

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Still in progress. Board shortened now 160mm x 80mm. Found models of tubes on the internet. The small tubes even have golden pins.

I got the tube models from grabcad.com and the creator of EL34 and small tube (12AX7) is Andrew Whitham, United Kingdom.

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Edited by JoaMat
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The two fellows in the red circle are 2sa1486. Roughly 800mW each, maybe to-126 is a better choice than smd  stn9360…

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Thanks for feedback Birgir. Moved a1486s to main heat sink. Kind of work that’s easily done with help of netlist and a glass of doublewood 12 years.

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Hmm... should move a1486s half an inch to the right.

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6 hours ago, JoaMat said:

Hmm... should move a1486s half an inch to the right.

Being from Sweden, shouldn't that be more like 12mm (well, 12.7mm) instead? :)

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That's the weird part of PCB design, most of it is in mills or inches.  I do alignment in mm's as the whole fraction thing is just utter BS but for heatsink attachment... half inches are the golden rule. 

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I usually work with imperial system in Proteus as I find it pretty convenient. For my 10K Afternoon Run the metric system is way more comfortable.:rolleyes:

 

8 hours ago, mwl168 said:

Can KSA1156 be used in place of the 2SA1486 here?

The voltage cross 2sa1486 is 580 – 590 V. That’s why I chose between stn9360 and 2sa1486. I guess you could use a pair of ksa1156 and split the voltage cross them.

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I have made a t8k input stage board for my bh,with a little bit tweaking,they've been working for 4 months,and T2 input stage can work fine as well. 😁

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 @Kung  Interesting. Can you provide more information, pictures etc. of what you’ve done? I love all kind of modifications.

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I think I’ve done some real progress with twin input tube grounded grid. The board will be made with a CNC router. The red lines show the route for the end mill, 15mil or 0.38mm with 0.5 overlap so each cut is down to 7.5mil.

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Milled and drilled right side board today. Same size as the single tube input version. Here single and twin small tube side by side. If lucky Mouser package arrives tomorrow and if Proteus ratsnest works it should play soon. If I haven’t done something stupid…

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Edited by JoaMat
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Replaced the original right board with the dual small tube one.

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First power on without any funny smell, smoke or explosions. But both outputs at positive rail voltage. Back to schematic and after a while I found two mistakes I’ve done. I managed to correct them on the PCB which now looks awful but it plays music all right.

 

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Something like this?? Board size 3.95in x 6.9in, same as I use. Probably a lot easier if bigger boards.

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