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Re: I wanna tube! Please advise

Posted by Jenya (A) on November 2, 2001 at 10:51:25

In Reply to: Re: I wanna tube! Please advise posted by ck42 on November 1, 2001 at 20:27:49:

"early conclusion that I want to start off with a SET amp. The weird thing I seem to be seeing is that they all are basically the same circuit. It's doesn't appear that there are too many ways of designing an SET. "

I think it is good that you decided on SET. It will give you a very good reference baseline. As far as number of different topologies for SET, I think in a crude way you are right. There are few tricks that you can play with though. Ultrapath for example. Some people would also tell you that there are 11 ways of implementing parafeed, which is another variation of SE. Power supply designes can vary from two $0.05 diodes, couple caps and resistor to a heavily regulated one. CCS loading is another trick worth of playing with. I am sure there are more.

"And if this is indeed the case, then it would be a no brainer to just make one and then tweak it via better componetry and minor circuit mods. I mention this because it seems to contradict the idea of 'designing a better one' vs. the kits."

I don't know if 'designing' a better amp would be an objective. Afterall, as far as I understand, all tube circuitry theory was pretty much complete by 1950-60. Not much you can invent there. However, ending up with a better amp than you would get by assembling a kit is a very achievable goal. As I mentioned above, there are few variable that you can play with to end up with a better sounding design.

"The one thing I haven't been able to figure out yet is the multiple tube stages that I see in most schematics. I understand the input stage, but then the plate goes right into the grid of the next stage on so on. What exactly is the purpose of this?"

After you finish reading your book, you will get a better idea how this works. In the nutshell, tube is a voltage amplifying device. When current passes through a first stage tube there will be a voltage drop across it. This voltage is applied to the grid of the next stage just like the one that was applied to the grid of the firts tube from your CD player. You are describing a dirrect coupling. Some circuits use a decoupling capacitor between stages.

By the way, if you decide on making headphone amp, you may not need multiple stages. My current version consists of only only stage that serves both for amplification and output, all thanks to a remarkable qualities of 6C45 tube. The simplest SE disign that can exist.

Regards,
Jenya

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