Building a valve amplifier

[horias2000]

Oh, if there's a pot involved, the imbalance you're getting is better than usual. Stepped attenuators might be a touch better (at a huge cost and size premium), but only a touch. You have a good result there.

Yes, there's a pot involved
I've added a pre-amp before the power amp stages so that I can exploit the entire power for different input sources. It's a simple schematic shown below.

It goes from about -75dB to 10dB. I did have some issues with the pot as I used some recycled pots from previous projects and some were defective (probabbly too much abuse when desoldering them from other boards). I will replace the pot at some point just to see if there is a difference. Bunt not anytime soon as I do not have the time right now. It sounds like a great activity around Christmas

 

[horias2000]

So, what do you think about it now? I built a kit WAD KT88 amp in 2001. Many prefer 6550 tubes, you may well prefer the mids.

For now I'm still using the JJ tubes I used during the development of the amp. These measure pretty good and sound very nice. I did look for other options form different manufacturers but at the moment I didn't buy any. I was looking at Genalex Gold Lions, Psvane and TAD. I know there are a lot of discussions around brands of tubes but I did not notice any difference. I built another amp like the one presented here, for a friend of mine and I used PSVANE KT-88s and 12AX7s and EH 12AU7s. The amp did measure a bit better in thd and thd+n (2-3dB better) but I could not hear the difference. I did notice though that the JJ tubes use higher quality materials. The glass is thicker and the pins seen stronger. But as a more general question, what brands of tubes do you guys recommend?