The ultimate DIY? A Stax SRM-T2!

[JimL]

Congratulations, indeed!

 

Now, as you may know, the T2's backbone is the same as the SRX Plus, it's just difficult to see because of the forest of solid state parts that surrounds it, most of them to replace two capacitors (per channel) in the SRX.  So, now you need to build the SRX Plus and see how cheap and simple you can go and still get great sound. 

[HemiSam]

ouch...

HS

[mypasswordis]

Again, the input stage is not a cascode in the SRX so they really aren't the same.  Also, the T2 has 6 total amplification stages, the SRX has 3. 

[justin]

1 hour ago, JimL said:

Congratulations, indeed!

 

Now, as you may know, the T2's backbone is the same as the SRX Plus, it's just difficult to see because of the forest of solid state parts that surrounds it, most of them to replace two capacitors (per channel) in the SRX.  So, now you need to build the SRX Plus and see how cheap and simple you can go and still get great sound. 

do this one next

[JimL]

Again, we are going to have to agree to disagree on description of the input stage.  D.R. Birt, who first described the circuit in Wireless World, calls it "long-tailed pair using cascode stages with cross-coupling."  Yes, there are additional stages in the T2, and the output stage uses grounded grid drive, but I maintain that the relation between the two is akin to the relation between a velociraptor and a T. rex.  You can see the common DNA in the two.

[mypasswordis]

Again, the SRX circuit is completely different from Birt's schematic. 

To say that they share the same DNA is to say that humans share 50% of their DNA with bananas. While true, a human and a banana are not the same thing. 

[JimL]

Weren't you going to run a simulation of the SRX input circuit to see if its amplification was similar to a standard cascode circuit?  I'd be interested to see what the results of that was.

 

As to the DNA issue, the SRX has a differential/long-tailed phase splitter input stage with two tubes sitting one on top of the other with the plate of the bottom tube connected to the cathode of the top tube (ignore the cross-coupling for a minute), and an output tube with the output taken off the plates.  These features are broadly similar to the T2 in topology.  The differences between a banana and a human is more akin to comparing a transistor radio to a T2.

Edited November 1, 2017 by JimL

[mypasswordis]

I believe I already proved that the SRX circuit is not a cascode. I spent about 2 straight weeks getting my improved T2 circuit to simulate correctly (with some help from Kerry), so I'm very cool with not touching spice for awhile and just concentrating on figuring out using the CNC I just bought. I'm also learning as much as I can about finance, marketing, and law, meeting with people from Skadden, Arps, Slate, Meagher & Flom tomorrow.

Edited November 1, 2017 by mypasswordis

[JimL]

2 hours ago, justin said:

do this one next

As I recall, that's the circuit that you tried to build, but found the OA2 tubes lost most of the signal?

[kevin gilmore]

although a lot more parts, and not all tubes, the T2 battery appropriately adjusted for voltage to replace the loss across the 0a2.

of course you could just use a 1uf cap across the gas tubes

[justin]

ssh i was trying to get JimL to do the T2 battery out of tubes (we can accept some neon)

Edited November 1, 2017 by justin

[kevin gilmore]

lots of floating filaments

 

[Whitigir]

So, I now learned my lesson to be very careful with T2 and tubes.  I couldn’t deal with Groove tubes EL-34 sounds, and while I liked the JJ on the Grounded Grid, it was too fragile to stand with T2.  Never again to stuck any JJ in the T2 anymore.  

Then nervously sticking in my next favorite in-line from GG tube rolls, the Quad RFT Vintage EL-34.  Didn’t dare to swap tubes without checking the balances and offset.  So balances was sitting at below 0.5V on both channel, and Offset was 5-6V on both channel.

The one thing I always noticed about GG and the T2 is that these output tubes affect the “turned on” to the 009.  The Groove tubes did an echo sound when Hv kicked on, and quick crack when turned off.  The RFT has a quick snap which is lower in volume than Groove tubes, and echoes when turned off.  In the GG quad Apex matched from JJ was dead quiet on turning on/off.  Sadly, it is not a brand to stick into the T2.  Now, why would they behave that way ? I have no clues.

anyways, I am enjoying the T2 with Quad matched ECC88 goldpin from JJ...again, love those JJ signatures.  Cross my fingers, and pray that they don’t give problems, and now RFT Vintage EL-34.  I just had to get away from bad tubes Signature, but also so much respect to how powerful T2 is, and that she can cook tubes easily.

So far, T2 is awesome!!! Wooooo

By the way, if any long time T2 owners can please share the experiences of reliables tubes, and bad tubes.  I think it would be excellent !

Edited November 1, 2017 by Whitigir

[JimL]

3 hours ago, justin said:

ssh i was trying to get JimL to do the T2 battery out of tubes (we can accept some neon)

Never going to happen.  As Dirty Harry said, "A man's got to know his limitations." 

[mwl168]

3 hours ago, Whitigir said:

So, I now learned my lesson to be very careful with T2 and tubes.  I couldn’t deal with Groove tubes EL-34 sounds, and while I liked the JJ on the Grounded Grid, it was too fragile to stand with T2.  Never again to stuck any JJ in the T2 anymore...

Have you considered the EH 6CA7 (the true beam tetrode ones)? IIRC, they may be a touch tougher due to larger plate structure and I personally really like their sound. They are literally a fraction of NOS EL34 price.

[Whitigir]

11 minutes ago, mwl168 said:

Have you considered the EH 6CA7 (the true beam tetrode ones)? IIRC, they may be a touch tougher due to larger plate structure and I personally really like their sound. They are literally a fraction of NOS EL34 price.

I have a quad of these Electro Harmonix 6ca7.  If it is safe, I would put it on :).  Thanks !

these ? Best NoS I have is rft and Winged C.  I refuse to go further the NOS road

 

Edited November 1, 2017 by Whitigir

[mwl168]

Yes, that's the one. 

I may get muds on my face but I am going to say it - I have those NOS EL34 you have plus Tesla and Mullard XF2 that I've used on my Blue Hawaii and Grounded Grid. I put these EH 6CA7 on and have not felt the need to use others. It's a different flavor than the EL34 and that's to be expected given it's physically different tube.

Got my matched quad from Upscale Audio so I paid more but I like the facts that Upscale burns these in for 72 hours prior to shipping so I have less to worry about defects from these current production tubes. 

[Whitigir]

1 hour ago, mwl168 said:

Yes, that's the one. 

I may get muds on my face but I am going to say it - I have those NOS EL34 you have plus Tesla and Mullard XF2 that I've used on my Blue Hawaii and Grounded Grid. I put these EH 6CA7 on and have not felt the need to use others. It's a different flavor than the EL34 and that's to be expected given it's physically different tube.

Got my matched quad from Upscale Audio so I paid more but I like the facts that Upscale burns these in for 72 hours prior to shipping so I have less to worry about defects from these current production tubes. 

 

Nice! I tried these on, and they have “blue / purple hue fluorescent”  or so I was told.....lol, never seen it in GG.  Anyways, these sound so nice!  Surprisingly the balances was dead-on around below 0.5V at cold start on both channel and offset is 5-6V on both channel.  When Hv kicked in, she gave a quick snap, but even lower than RFT

I hope this will be a reliable choice 

Edited November 1, 2017 by Whitigir

[GeorgeP]

3 hours ago, mwl168 said:

Have you considered the EH 6CA7 (the true beam tetrode ones)? IIRC, they may be a touch tougher due to larger plate structure and I personally really like their sound. They are literally a fraction of NOS EL34 price.

I always get confused by this whole some 6ca7 tubes are pentodes (relabelled EL34) and some (the fat bottle Sylvania/GE) are beam tetrodes. Not sure which was the intended one for theT2. But if there is cheap current production source of tubes that sounds better than all the new production "el34" tubes, and doesn't blow up the t2, then colour me interested.

[kevin gilmore]

The real original has el34 with the Richardson electronics National Logo made in USSR  about 1994

the 6dj8's were gold aero

 

Edited November 1, 2017 by kevin gilmore

[Whitigir]

4 minutes ago, kevin gilmore said:

The real original has 6ca7 with the Richardson electronics National Logo made in USSR  about 1994

the 6dj8's were gold aero

 

Where would you recommend to get these tubes ?

7 minutes ago, GeorgeP said:

I always get confused by this whole some 6ca7 tubes are pentodes (relabelled EL34) and some (the fat bottle Sylvania/GE) are beam tetrodes. Not sure which was the intended one for theT2. But if there is cheap current production source of tubes that sounds better than all the new production "el34" tubes, and doesn't blow up the t2, then colour me interested.

Yes, and same here.  May be sir KG can answer which one is intended more for T2

Not sure if it will blow up the T2, but so far she is singing.  You did have a tube that took out some part in the T2 before right ? What was it ?

Edited November 1, 2017 by Whitigir

[mypasswordis]

Not sure what the Gold Aeros are, but regular 6DJ8s shouldn't be used with the T2. They have a max plate voltage of 130V and the top tube sees about 130V. 

[Whitigir]

1 minute ago, mypasswordis said:

Not sure what the Gold Aeros are, but regular 6DJ8s shouldn't be used with the T2. They have a max plate voltage of 130V and the top tube sees about 130V. 

Ouch...and I am using JJ ECC88.  Will Sylvania do better ? How about those Beam Tetrode or Pentode ?

Edited November 1, 2017 by Whitigir

[mwl168]

Yes, it's a confusing topic for me when I was obsessed with finding "The Tube" for the Blue Hawaii and the Grounded Grid. 

I did a lot of reading including the history of EL34 and how the beam tetrode 6CA7 came about. From what I read, GE and Sylvania wanted to produce US-equivalent of EL34 without paying for the licensing, so they developed 6CA7 as a result which is a beam tetrode and not a pentode. However, many EL34 tubes back then were also labelled 6CA7 (many actually have both designations labelled on the tube) but I have not seen a true beam tetrode 6CA7 that is also labelled EL34 so far.

Many of the EL34 and 6CA7 information I read are in the guitar amp forums and many described the beam tetrode 6CA7 as a more tonally balanced tube while the EL34 is supposedly having an emphasized midrange. I decide to try the EH 6CA7 out of curiosity and that was that.

I liked them so much I started to search for NOS Sylvania and GE 6CA7 quad but ended up blowing my funds in new headphone.

This hobby is going to bankrupt me someday!   

[Whitigir]

Indeed this EH6ca7 is more balanced and neutral tonal body.  But really, many of the 6ca7 is just Pentode, and this one is Beam Tetrode.  They gotta affect somehow to the Circuit ? Does it matter ? The GG was a much friendlier amp in comparison to the T2 and it Power though. I have no clues regard tubes :(....a disadvantage for being younger generation 

Edited November 1, 2017 by Whitigir