Jump to content

The ultimate DIY? A Stax SRM-T2!


spritzer

Recommended Posts

@@bui501, I’ve no idea if the PBHVs will do or not – someone should try. But how about KSA1156? Max voltage cross pnp in battery is around 370V. As for space it might be a little tight though.

On ‎2018‎-‎04‎-‎18 at 9:54 AM, bui501 said:

Even the more recent sands are starting to be difficult to source.

The squirrels sit on them.

Link to comment
Share on other sites

15 hours ago, JoaMat said:

@@bui501, I’ve no idea if the PBHVs will do or not – someone should try. But how about KSA1156? Max voltage cross pnp in battery is around 370V. As for space it might be a little tight though.

The squirrels sit on them.

Awe, Nuts! :-D

13 hours ago, spritzer said:

The KSA1156 should work and then there is the 2SA1627 which is in current production in China.  They are either a TO126 and Dpak which is just annoying... 

Thank you, JoaMat & Spritzer. I’ll look them up on mouser. This is the very last sand I need to source from the T2 BOM... assuming none of the older items are not fake (knock on wood).

 

Link to comment
Share on other sites

19 hours ago, bui501 said:

Awe, Nuts! :-D

Thank you, JoaMat & Spritzer. I’ll look them up on mouser. This is the very last sand I need to source from the T2 BOM... assuming none of the older items are not fake (knock on wood).

 

Test it first Vinh.  Make sure you meticulously test them through and through :)

Link to comment
Share on other sites

7 hours ago, Whitigir said:

Test it first Vinh.  Make sure you meticulously test them through and through :)

:)Thanks.  I'm planning to after my experience with the counterfeit CREE parts from alibaba during my Carbon build.  I've purchased the DY294 transistor tester that was recommended a few years back in this thread.  Is there are better/more accurate equivalent that you're using?  My DY294 sometimes gives me a bad reading for a known good part from mouser.   I would purchase a curve tracer for this project, but they all seem to be prohibitively expensive compared to all other lab equipment. -Vinh

Link to comment
Share on other sites

Yes - C3 in my schematic above.  Joachim suggested a value of 6.8uF works best here. 

I've had it up for several hours now and and it seems very stable.

I also added a 1K resistor from the -560V rail to the collector (external to this board).

Edited by Kerry
Link to comment
Share on other sites

Not to my knowledge.  I believe it brings the stators to a more positive voltage (closer to the 580V bias).  AFAIK, this has been in the DIY T2 build from the beginning and has not caused any issues.  From a volume perspective, it's not particularly loud and I can have the headphones on my head when I power down without discomfort.

  • Like 1
Link to comment
Share on other sites

2 hours ago, Kerry said:

Not to my knowledge.  I believe it brings the stators to a more positive voltage (closer to the 580V bias).  AFAIK, this has been in the DIY T2 build from the beginning and has not caused any issues.  From a volume perspective, it's not particularly loud and I can have the headphones on my head when I power down without discomfort.

The thump shouldn't do any damage but it might be a good idea to follow the original and add some relays to the output.  Stax used a 4PDT Omron relay but it is rated to nowhere near the specs we really need. 

  • Like 2
Link to comment
Share on other sites

If running short of 2sj79 one could rebuild the T2 to something similar to a Grounded Grid. I removed j79s, 750R resistors, a1486s and corresponding LED. Works/ed like charm. Unfortunately right channel started to obstruct after a while. Perhaps this kind of modification isn’t appropriate.

For the time being I run left channel to both sides.........

Edited by JoaMat
Link to comment
Share on other sites

Thanks a lot George, but I actually have a small stock of j79/k216 myself. Living in the middle of nowhere you need to be prepared.

Have been socializing with the faulty channel today and we are now both happy again. Maybe it’s more of a Grounded Grid with dual tube input and active batteries than a T2.

Picture below shows the modded T2. No j79/a1486 at the output stage. Upper right the middle a1486 is missing – replaced with resistor so upper tube grid voltage is set by a voltage divider. If you have a well defined supply voltage you don’t need to send 2.5mA through a 27K resistor – I think.

_MG_1606.thumb.JPG.1815e00f0bfa3b1d78c37898179327f8.JPG

Edited by JoaMat
  • Like 2
Link to comment
Share on other sites

My T2 PSU differs some from the original DIY T2 PSU as I have a -560V section which is as capable as the -500V. So with this modification the only work the -500v is doing is to set the 6CA7 G1 potential.

LTspice simulation I’ve done indicates that -500V at G1 might be desirable. But I don't trust myself doing this kind of work in LTspice.

Below schematic: removed Q24,Q25,Q28,Q29,LED, R48,R49. Added jumpers between drain k216 and cathode 6CA7.

5af2c069dc6e4_Modifiedt2schemop.thumb.jpg.82486b1ca90b7108696b613eb780c3e2.jpg

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.