|
Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
|
|
|
Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
|
In Reply to: A question 4U Doc. posted by Tom S. on June 17, 1999 at 06:21:53:
My personal prejudices go against using parallel tubes unless you are trying get budget power as in the ParaSEX, because I've heard improvements in clarity when comparing a single vs. parallel tubes. But I won't dispute that the EAR 12AX7 amp sounds nice.You have to keep the plate impedance in mind when you look at this type of amp design, which I would consider a relatively advanced project. The fewer tubes, the higher the total plate resistance ( which is way high with a single 12AX7, remember). You won't easily find an output trans that will work.
The alternative might be to use the fewer 12AX7s as cathode followers, then you could get a very low output impedance from the circuit. But the cathode follower has unity gain or less, so of course then you need to design a good gain stage in front of it, and it starts to get complex fast.
I think the spud in it's most simple form would be a great first scratch built project, because you can throw a lot of different parts at the circuit, and get a great idea of what each change is doing. The sonics of virtually every change comes thru with the single gain stage- resistor vs. battery on the cathode, different operating points, power supply mods, etc. You could build up to a really cool one with a CCS on top and an inexpensive parafeed setup using a cheap PA matching trans or an nice old PP trannie, or a fancy nickel parafeed one like the EXO-45. Use a shunt regulated power supply, really premium wirewound resistors, be careful to properly bypass the heaters and stop the grid to avoid oscillation, and it would sound super nice.
I did a parallel version of the original spud to get the power up a bit, but the single tube design has a certain bizzare purity to it that is very attractive.
Another alternative would be the single 6DN7 amp something like one we published several years ago. Not a single triode amp, but a single tube, potentially a very nice direct coupled amp, as Paul Joppa designed a few years later, and Ron Welborne did in a 6EM7 parafeed version.
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Re: A question 4U Doc. - Doc B. 06/17/9909:59:51 06/17/99 (1)
- Re: A question 4U Doc. - Tom S. 10:55:18 06/17/99 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
