You should have this amp refurbished, completely if possible. At the very least, you're going to need filter capacitors, (sounds like one or more of the old caps have shorted) plus you will need the rectifier tube. You're lucky the PT didn't go south as well! I would invest in a Variac and reform the old caps for the next amp you buy, but for this one, it's too late.
~~John~~~
~~John~~~
coyotesgator said:
I own a pair of the same amplifiers, . both decided to quit on me over the last year. Need to refurb them.
I recapped one of them (signal caps only) a few years ago, but the smear you speak of remains (though I'd describe it as tubby bass) . It only really bothered me on inefficient speakers though (less than 90dB)
Two things I could think off
1. beefing up the power supply
2. implementing the williamson circuit mods. detailed on the chimera labs page http://www.chimeralabs.com/williamsmod.html .
Some audio enthusiasts have noticed that the amplifiers sound better when they are connected to efficient speakers. In fact when they are connected to less efficient speakers, two design flaws surface. At higher output levels they exhibit high levels of distortion and instability. In 1961, Talbot M. Wright published an insightful analysis of the circuit in Electronics World, highlighting these two problems. Fortunately he also told us how to fix them and his recommendations form the basis of this article.
Hope that helps.
I'm not thrilled with his approach, either. The main issue with the Williamson is LF stability, which is best addressed by coupling caps- if the time constants of the two RC couplings are staggered by 5:1 or more, the LF stability will be much improved. I wouldn't fool with the operating points; they are chosen for best linearity. A properly operating Williamson driver has more than enough capability to drive its output stage to clipping.
The writer is correct about replacing 12AU7 with something more linear.
Changing the cathode bypass cap on the output stage will indeed extend the LF response. The cost is much worse overload recovery. If you're using a small tube amp to reproduce high level deep bass, I don't have much sympathy...
edit: I see that this site touts "high slew rate capacitors." Res ipsa loquitur.
The writer is correct about replacing 12AU7 with something more linear.
Changing the cathode bypass cap on the output stage will indeed extend the LF response. The cost is much worse overload recovery. If you're using a small tube amp to reproduce high level deep bass, I don't have much sympathy...
edit: I see that this site touts "high slew rate capacitors." Res ipsa loquitur.
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