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Re: The worst sort of naysayer BS!

Posted by kentaja@yahoo.com (M) on September 17, 2004 at 15:04:56

In Reply to: The worst sort of naysayer BS! posted by Keith Lockwood on September 17, 2004 at 14:27:05:

Can you point out to me where I discounted your experience? I don't believe I did.

I questioned, and that was it, questioned, the assertion that the amp has no cathode follower. I was assuming you were referring to the typical driver stage in ARC amps executed as a cathode follower. And again, I did not claim the VT130 had a driver stage executed as a cathode follower. I said I did not know since I had never seen a circuit diagram of the VT130. My error here was in assuming. I should have asked you to clarify this point since ARC input stages typically employ cathode followers in several locations, with the driver stage generally always a cathode follower.

What I did say was that ARC amps, from the beginning, share a very common theme when it comes to circuit topology. A look at their circuits over the years will confirm this point. UL output stages are virtually identical since day one. Some changes in operating points, or number of tubes, but the same UL circuit. Input stages have gone through many revisions, but still sport similiar circuit topologies, even with the newer generation of hybrids. Changes in tubes have caused them to either scale up or scale down the circuit complexity based on gain, interstage coupling, actual tubes used, etc.

I did not say anywhere that running KT88 in VT130 was an OK thing to do. I have visited with ARC on this topic in the past, and in general, ARC frowns on KT88, KT90 or just about any other tube in the circuit, unless the circuit was designed around that particular tube.

Whether or not the failure of the VT130 was due to using KT88 in the output stage and the circuit having no driver/cathode follower stage, I do not know. How could I? But my guess here is the KT88s where probably of questionable quality and bit the dust, taking out some of the amp. Again, just my guess based on a sketchy description of actually what happened and having a great deal of experience with ARC amps and bad tubes in ARC amps.

Actually, my real failure was in responding at all. Just trying to pass on a little information regarding ARC tube circuits, in general.

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