The ultimate DIY? A Stax SRM-T2!

[JoaMat]

heat shrink, first thing in the morning.

[nopants]

are you planning on implementing the solid state input stage again?

[JoaMat]

Didn't found  heat shrink wide enough. So printed some covers for the connectors. Not so elegant but it serves its purpose.

16 hours ago, nopants said:

are you planning on implementing the solid state input stage again?

No, but now that you brought it up - well, why not.....

[Kerry]

I love your mind and 3D printer

[JoaMat]

OK, now it’s done. Swapped the small tubes for solid state adapters. Kept +250V voltage and battery voltage unchanged. The 2SC3840 dissipate some 0.8W each. Might need small heat sinks. If you decrease voltage by 100V you also decrease power dissipation to >1/3W.

And yes, they need covers. Working on it.

[nopants]

Some metal covers like what schiit uses might work, maybe you can just scavenge some nice-looking tube shields?

[luvdunhill]

I suppose calling them "eneimas" might be close of a trademark violation to the reality of Mikhails's "enigma" cable design.

[8street]

On 02.04.2016 at 11:50 PM, JoaMat said:

T2 with Emission Lab’s EML 20B-V4. Transformer to left is for filament 4 x 5.0V. Adapters are made by some help of a 3D printer, Teflon tube sockets, slauthered Neutrik XLR connectors, two pole male connectors. All held together with really good Loctite super glue.

Once I have used KT66. They do not require any mods. Just put and listen. 

[JoaMat]

Beautiful!

 

[spritzer]

Well KT66's are utterly incompatible with the amp and will not last long but please go ahead and blow up your T2. 

Read the fucking datasheets!! 

[JoaMat]

Birgir is most certainly right about KT66 and T2. EL34 and equivalent are the one to use.

 

Regarding datasheet. Most of us aren’t competent enough to read them, including me. Anyhow I make a try. KT66 max working voltage is 500V and absolute max is 550V. DC voltage on output tube of T2 is about 450V. You will probably easily overstress KT66 and eventually maybe destroy them. If that happens – please let us know. I’m especially interested in effects on the amplifier.

 

I’m sure that there are members out there that can tell us pros/cons KT66 with T2.

Edited April 5, 2016 by JoaMat

[kevin gilmore]

reminds me of mikhail hand picking el34 that would work with 400v on the cathode. And the people involved remember how that turned out.

kt66 has to go boom eventually and take the j79 and k216 with it.

Edited April 5, 2016 by kevin gilmore

[spritzer]

If you use old GEC KT66's then maybe they might work for a while as they were so massively over engineered but anything from the 70's and on wards will not last long. 

This can't be stressed enough, the EL34 is a oddity amongst the octal power tubes so the logic that any of them will work just isn't even remotely true. 

[8street]

Of course I read the datasheet. And I know maximum parameters in T2. You should use only tubes in excellent condition and in fully turned and working amp.

But I preffer EL34. Probably KT88 would work as well.

[JoaMat]

There are all kinds of EL34. Some good and some better.

 

A few years ago I acquired those EL34. Probably manufactured in Eindhoven Feb. 1951(left) and Feb. 1954(right).

 

[DefQon]

I'm going to start putting in KT66 and KT88's in place where EL34's are required in my amps. 

I'll post pictures of the aftermath if it happens.

[GeorgeP]

18 minutes ago, JoaMat said:

There are all kinds of EL34. Some good and some better.

 

A few years ago I acquired those EL34. Probably manufactured in Eindhoven Feb. 1951(left) and Feb. 1954(right).

 

Those look like the old EL60 with factory attached 8-pin sockets and re-labelled as EL34.

 

[JoaMat]

If interested in the story of EL34, I recommend Guide to the EL34 / 6CA7 by Pasquale Russo.

[s_r]

Figured I should get other opinions as well. Now that I have a scope on hand, where/how should I go about trying to track down the noise problem in my T2? I haven't tried poking around yet, since I don't want to risk blowing up the scope.

[Craig Sawyers]

What scope, what probes?  Highly specified Tektronix probes only handle 300V for a x1 and 450V for a x10 non-destructively.  Generic probes can be much less, or poorly specified.

[luvdunhill]

I use a Tek P5210.

[Craig Sawyers]

Yup - that'll do it. Nice probe. If you can cope with x100 and x1000 attenuation.

[luvdunhill]

The scope readout is adjusted automatically, which is convenient. The P5205 might be a better choice.

[s_r]

13 hours ago, Craig Sawyers said:

What scope, what probes?  Highly specified Tektronix probes only handle 300V for a x1 and 450V for a x10 non-destructively.  Generic probes can be much less, or poorly specified.

A Rigol DS1054Z, and these are the additional probes I got.

[Craig Sawyers]

OK - decent scope, but be careful what and where you probe.  My tendency would be not to probe with the T2 turned on - one slip with the ground lead, probe tip or your finger could spoil your day big time.  I would turn the T2 off, attache probe connections and turn on again.  But bear in mind that any complex feedback amplifier can oscillate - IIRC there are the odd single figure pF capacitors in there to stabilise the amp.  Also probe impedance can modify the effect - either stopping the oscillation, making it worse, or changing the frequency.