[Freo-1]

Yes, damper tubes do make great rectifiers and exceed 5AR4s in many ways.

The 6T4 is interesting but it is a much smaller tube with higher mu. It would not be so good driving a transformer. The mu also varies a lot with plate current, more so than the 12B4 and 6AH4 which are lower and more constant mu. The last two I mentioned were used as vertical output tubes. A vertical amplifier in a TV set is basically a class A power amplifier and has to be very linear so as not to compress or expand the picture at the extreme top and bottom of the screen.  Vertical output tubes make the best SE output tubes. This preamp is basically a little power amp and could drive headphones with the right ratio transformer. The 6T4 is a UHF tuner tube and perhaps its variable mu was a design factor which we do not want for audio. Its the same problem I saw with the 6DJ8 vs 6ES8, the first being constant mu and the second variable. You can read about that here.  http://tubeaudiostore.com/suitof6dfora.html

Good stuff!  When I first researched this over in a DIY website, there were several posts about using the 6AH4 as a power amp.  I absolutely love it as a preamp.  Regarding the 6T4, probably not worth using as a preamp.

I was warned about the 6ES8 many years ago by a honest tube vendor.  Thanks for pointing this out.

[JoshK]

I really like this concept for a preamp, except that I think I might modify it somewhat making it more Raven like.  http://www.nutshellhifi.com/Raven-MarkII.gif

Essentially making it a differential preamp.   This buys me a few things.  #1 can be used with both single ended and XLR inputs/outputs.  I have both in my system.   It lowers the Zout by half and I want to be able to run 15' interconnects between my preamp and amps.  I have many if not most of the parts sans the output transformer and I have a large preamp chassis to do this in.

http://www.audiocircle.com/image.php?id=9454

In that chassis (lots of room) I have six RCA inputs, but can easily change two to XLR and dual RCA outputs, can add XLRs.   It uses Silk Audio TVCs
http://www.sacthailand.com/Transformer_Attenuator.html

So I'll need to do some modifications.   The question is whether to use it on the output like Thomas Mayer does or at the input.  I have Jensen input transformers unused at the moment, so I could use those at the input instead.

[Freo-1]

I really like this concept for a preamp, except that I think I might modify it somewhat making it more Raven like.  http://www.nutshellhifi.com/Raven-MarkII.gif

Essentially making it a differential preamp.   This buys me a few things.  #1 can be used with both single ended and XLR inputs/outputs.  I have both in my system.   It lowers the Zout by half and I want to be able to run 15' interconnects between my preamp and amps.  I have many if not most of the parts sans the output transformer and I have a large preamp chassis to do this in.

http://www.audiocircle.com/image.php?id=9454

In that chassis (lots of room) I have six RCA inputs, but can easily change two to XLR and dual RCA outputs, can add XLRs.   It uses Silk Audio TVCs
http://www.sacthailand.com/Transformer_Attenuator.html

So I'll need to do some modifications.   The question is whether to use it on the output like Thomas Mayer does or at the input.  I have Jensen input transformers unused at the moment, so I could use those at the input instead.

Thomas Meyer's design already is designed for long cable runs as a single ended configuration.  I wanted better overall control of the volume, so i went with the Zhomzo stepped attenuator with the REX resistor upgrade.

http://khozmo.com/products_dale_shunt.html

Mine is connected at the input.  This is without question the quietest and most natural sounding preamp I've ever heard.  It actually transformed the power amp performance to a whole new level. 

I love the Heyboer transformers and chokes. 

Keep us in the loop.  Looking forward to reading about your project.  Good Luck! 

[JoshK]

I think I still want to go balanced because of half of the Zout, ability to go single ended to XLR and back, ground lifting and distortion cancellation.   The latter I wouldn't always see as beneficial but in the linestage I think it is.  Because the 6AH4 is single triode, you can mix and match easily to gain the best match.

[Freo-1]

Trust me, distortion is not going to be an issue with this design single ended.  The 6AH4 is a truly outstanding tube in this application. 

One thing is if you put the volume control on the front end, then the output needs to be floated to ensure there is no hum.  I'm keen to see  what you come up with.   

[JoshK]

I'm not particularly concerned with distortion SE, but the other aspects I'm leaning towards.   I have the passive Silk Audio TVC and the active diysoundgroup Tram OTL II linestage to compare.  I don't need gain in my system and wonder why some do.

Both my linestages are awesome, so this is more of a convenience, and appropriateness factor.

[Roger A. Modjeski]

Trust me, distortion is not going to be an issue with this design single ended.  The 6AH4 is a truly outstanding tube in this application. 

One thing is if you put the volume control on the front end, then the output needs to be floated to ensure there is no hum.  I'm keen to see  what you come up with.   

It would be nice to measure the distortion. A 6922 in a typical circuit has about 0.1% per volt output. Since you have a step-down transformer at the output it would be interesting to know the THD. It's what we do in class.

Floating the output is an excellent way to eliminate ground loop hum. Great idea

[Freo-1]

It would be nice to measure the distortion. A 6922 in a typical circuit has about 0.1% per volt output. Since you have a step-down transformer at the output it would be interesting to know the THD. It's what we do in class.

Floating the output is an excellent way to eliminate ground loop hum. Great idea

I am curious as to the distortion measurement as well.  I will have to see if I can get that measured.