[Xcalibur255]

By old skool you mean you're not using any modern silicon for power filter and regulating, but perhaps you've also come up with something more clever than the typical CLCLC filtering scheme?

 

[L0rdGwyn]

By old skool you mean you're not using any modern silicon for power filter and regulating, but perhaps you've also come up with something more clever than the typical CLCLC filtering scheme?

Nope, as built the amplifier has no silicon whatsoever, it's just tubes, resistors, capacitors, inductors. The power supply isn't regulated, it is a passive filtered supply, nothing clever you can do regulation with vacuum tubes, but transistor-based circuits are going to be higher performing in general. Even a modestly performing transistor-based series regulator will outperform a gigantic choke. They are more prone to failure however and some are becoming difficult to source reliably. Always a balance of compromises.

 

[JazzVinyl]

Technical question for @L0rdGwyn -

When you have an SEPP headphone amp...I have always heard that the positive and negative portions of the input are split, and amplified seperately.
And that the output transformer's job is to rejoin the +/- portions of the output wave form, just prior to feeding the cans...

Is that in fact, what it does?

 

[L0rdGwyn]

Technical question for @L0rdGwyn -

When you have an SEPP headphone amp...I have always heard that the positive and negative portions of the input are split, and amplified seperately.
And that the output transformer's job is to rejoin the +/- portions of the output wave form, just prior to feeding the cans...

Is that in fact, what it does?

What you are describing is more in line with a conventional push-pull amplifier, which is different than SEPP / SRPP. In a push-pull design, the input signal is split into its respective positive and negative halves by a circuit element called a phase splitter (several different ways to do this), then the respective positive and negative signal are amplified and recombined at the output transformer. This is a balanced design.

In SEPP (single ended push-pull), two triodes are stacked on top of one another and the cathode of the top triode is connected to the plate of the bottom triode with the two tubes in series. While it looks like a single-ended circuit (not balanced), the actual function of SEPP is push pull with the resistor between the cathode and plate of the two tubes acting as a phase splitter. Like other push pull designs, the circuit should be optimally balanced, and this is the reason why a SEPP circuit is usually designed and optimized to operate into one load impedance, as changing the load will disrupt the balance of the push-pull circuit. It does not require an output transformer to recombine the signals and is typically capacitor coupled.

What you get out of a SEPP circuit, practically speaking, is a stage that has voltage gain (like a common cathode amplifier circuit) and a low output impedance (like a cathode follower). So you get an increase in voltage amplification but also some output buffering. Alternatively, you can use one of the triodes as a common cathode gain stage followed by the second triode as a cathode follower for a similar functionality without the push-pull optimization needs. People tend to argue over which approach is better.

There is an excellent article here from TubeCAD that explains SEPP in detail, but it is a bit technical.

https://www.tubecad.com/may2000/index.html

Here is a screenshot of the general circuit.

 

[L0rdGwyn]

Rereading your question @JazzVinyl , if you have a transformer coupled SEPP headphone amplifier, then RL in the circuit above is replaced with the output transformer and the transformer primary serves the same purpose as RL, it is the load for both positive and negative halves of the output signal, so in a way the transformer does combine the two halves.

 

[JazzVinyl]

Rereading your question @JazzVinyl , if you have a transformer coupled SEPP headphone amplifier, then RL in the circuit above is replaced with the output transformer and the transformer primary serves the same purpose as RL, it is the load for both positive and negative halves of the output signal, so in a way the transformer does combine the two halves.

Yes, thanks for that 2nd look, @L0rdGwyn.

This one is SEPP, w/output transformer and also capacitor-less at the output stage, thanks to the lack of DC there, said to be possible via a highly refined (via SS components) power supply.

 

[Zachik]

@L0rdGwyn Have you heard of that tube tester?
http://www.thebestamp.com/Testing_Equipment/AudioTubeTester-3.php

I am debating moving from the 100% manual tube tester I got, to something more modern such as that one... Amplitrex 1000 is way more expensive!

 

[L0rdGwyn]

Yes, thanks for that 2nd look, @L0rdGwyn.

This one is SEPP, w/output transformer and also capacitor-less at the output stage, thanks to the lack of DC there, said to be possible via a highly refined (via SS components) power supply.

Sounds like an interesting amp!

 

[L0rdGwyn]

@L0rdGwyn Have you heard of that tube tester?
http://www.thebestamp.com/Testing_Equipment/AudioTubeTester-3.php

I am debating moving from the 100% manual tube tester I got, to something more modern such as that one... Amplitrex 1000 is way more expensive!

No I have not, last time I heard of this guy I was looking at his tube-based DACs years ago, I think someone recommended him to me...

Looks like an interesting tester though, pretty unusual for a tester to give you a gain reading. Just want to be sure it's going to be able to test everything you want, I saw there is an DHT expansion module, since you have a DHT amplifier coming you definitely want to be able to test those tubes!

 

[Zachik]

Looks like an interesting tester though, pretty unusual for a tester to give you a gain reading. Just want to be sure it's going to be able to test everything you want, I saw there is an DHT expansion module, since you have a DHT amplifier coming you definitely want to be able to test those tubes!

I agree the tester looks very interesting!
IF I end up buying this one - I will most definitely get the optional DHT expansion box.
But before committing to such an expense - I am looking for (unbiased) opinions on the tester. I was hoping you (or someone else on this thread) know anything (good or bad) about this tester...

 

[L0rdGwyn]

I agree the tester looks very interesting!
IF I end up buying this one - I will most definitely get the optional DHT expansion box.
But before committing to such an expense - I am looking for (unbiased) opinions on the tester. I was hoping you (or someone else on this thread) know anything (good or bad) about this tester...

When I get some time, I'll take a closer look at the info page and the video and see if I can think up some pros and cons.

 

[Zachik]

When I get some time, I'll take a closer look at the info page and the video and see if I can think up some pros and cons.

Thanks - much appreciated!

 

[L0rdGwyn]

Thanks - much appreciated!

So something that comes to mind for me - this tester has a maximum 200V B+ supply. Many tubes in their datasheets give operating parameters at higher voltages, 250V or 275V is common. When testing, you may not have a reference value to compare the tube to since measurements will be done at lower voltages. The gm for a tube will be different at 200V vs. 250V for example. Practically, it's fine as you can say the tube's gm is "in the ballpark" of NOS in the datasheet and has appropriate gain, but you will not be able to use the datasheet measurement parameters directly if they are over 200V B+. Other than that, as long as it tests all of the tubes you want to test, it has a lot of great functionality that isn't included on many tube testers, like gain measurements, sine waveform, noise testing. Includes gas and shorts as well.

 

[Monsterzero]

Got out of the ZMF ecosystem for a change of pace last night, and donned the grossly unknown and underrated Sennheiser HD250. Man these headphones scale like mad!
The VC is more technically proficient, but if you enjoy a punchy sound with other wordly sub bass, its an amazing headphone, especially for 75 bucks shipped, lol! Still the best bargain to date in this hobby.

Airmid- Ken Rad 6J5+Tung sol 5998
TRP-WWll era RCA 5R4GY+Sophia Electric EL34

 

[L0rdGwyn]

Got out of the ZMF ecosystem for a change of pace last night, and donned the grossly unknown and underrated Sennheiser HD250. Man these headphones scale like mad!
The VC is more technically proficient, but if you enjoy a punchy sound with other wordly sub bass, its an amazing headphone, especially for 75 bucks shipped, lol! Still the best bargain to date in this hobby.

Airmid- Ken Rad 6J5+Tung sol 5998
TRP-WWll era RCA 5R4GY+Sophia Electric EL34

Looks awesome, yeah I sort of regret selling mine now, they really are great headphones. I think I mentioned this before, but I had some difficulty getting a good seal with my pair, I was using ZMF universe pads at the time. I might give them another shot someday.