My New Iron for Single Ended 2a3

[MrCurwen]

soulmerchant:

Please do note that I never made such a claim. Is this amp is one of the best SE that I ever built? sure. The best in the universe? That's a pretty big claim!

I realise nobody made such a claim.I simply meant, that if one sees room for improvement, one should throw around ideas in an environment made for sharing ideas. I saw room for improvement, so I chimed in.

But I now look very much forward to your schematic with pictures of your build. This is a DIY board so do feel free to share.

Here's the beginnings: http://www.diyaudio.com/forums/tubes-valves/273896-mr-curwens-single-ended-adventures.html

goldenbeer:

Look at the protection diode in my circuit. This should take care of any hard turn on issues as well.

Yes. However soulmerchant raised the issue of turn on regarding the gyrator circuit.

If you are referring to your sims, at such low distortion levels, the tube models and simulations are notoriously unreliable wrt distortion levels. You need to resort to real world measurements. But then, you would probably only find that in this case, distortion varies more between different brands, samples and batches of tubes than the circuit topologies discussed or anything else...

Sims are what they are. However I could not disagree more on the distortion varying more between tube brands and such than between topologies. Load lines matter. A lot; no two different brand in spec tubes make even 5% as much difference as two different load lines. This is very easily heard in my experience.


Since I realised I'm way off topic, I'll continue in the other thread. Apologies for that and carry on.

 

[disco]

... Sims are what they are. However I could not disagree more on the distortion varying more between tube brands and such than between topologies. Load lines matter. A lot; no two different brand in spec tubes make even 5% as much difference as two different load lines. This is very easily heard in my experience.

ri of a worn out tube is higher than a fresh tube, one would expect that property to be noticeable in marginally designed circuits, or in a circuit where leveraging of impedance takes place, like here with the bootstrap circuit.

 

[soulmerchant]

Dear All

Sorry for not having much time to add to my thread. In any case I would like to share with you the latest power supply I am using.

I'm using LCLC after the rectifier, using a Lundahl LL1694 (filament choke), 10-20uF then split to separate windings of a Lundahl LL1638, then 35-40uF.

Some day I might try Curwen's suggestions, but right now I'm too busy with my day job and to be frank and honest.. it just sounds too good to fiddle with right now.

If I have some time this weekend, I will try to measure THD using an audio analyser software and my old laptop.... Wish me luck with this.

 

[soulmerchant]

ri of a worn out tube is higher than a fresh tube, one would expect that property to be noticeable in marginally designed circuits, or in a circuit where leveraging of impedance takes place, like here with the bootstrap circuit.

Still won't make a difference over time since MU changes very little as a tube ages. Some more plate resistance won't make a difference at all in this circuit. Do the calculations or an accurate simulation and you will see...

 

[MrCurwen]

disco, it is because of the leveraging that plate resistance is not as critical.

 

[jmotzi]

Dear All

...I'm using LCLC after the rectifier, using a Lundahl LL1694 (filament choke), 10-20uF then split to separate windings of a Lundahl LL1638, then 35-40uF....

Why did you change from your previous PSU in Post #63? Was it to achieve a simpler design, or higher B+, or .... ?

JM

 

[soulmerchant]

Why did you change from your previous PSU in Post #63? Was it to achieve a simpler design, or higher B+, or .... ?

JM

Chiefly for simpler design. I would like to use these filament chokes for some other things as well (such as on filaments). But I also find the slightly higher B+ also sounds better. There appears to be a bit of a sweet spot with A-K close to 240VDC...

You can push up the B+ up bit more by using 6AU4 (which also has lower plate resistance).

Another option would be to build a voltage doubler circuit using silicon diodes. That could be a nice option depending on the Mains transformer at hand.

Ian