[Roger A. Modjeski]

Has anyone any experience, circuits, thoughts or ruminations on the value of using low Mu triodes (e.g. 6C33, 6AS7, 6080) in cathode follower or common cathode circuits? These tubes are difficult to bias and hold it.

I have worked on Atmasphere amps and have them down in my notes. How about the Joule Electra amps using the 6C33?

[Srajan Ebaen]

The Almarro A318B is just such a design - www.almarro.com. I experienced little bias drift during my time with it but one 6C33C got noisy and was replaced. Superb sounding piece, very linear, very dynamic, very transparent. Very much like a 45 on steroids. I've heard of designers using servos to lock in the bias. A forthcoming class A p/p design will have adjustable negative feedback and adjustable positive current feedback.

www.ayonaudio.com too makes 6C33C integrateds and amps but not sure on their circuit.

[jrebman]

Roger,

I'm not sure what their circuit configuration is, but I've had the opportunity to listen to the Lamm ML2.1s many times and aside from being one of the nicest sounding amps I've ever heard, I know the owners bias them approximately every month or so -- only because that seems to be the most reliable way of detecting when a tube is going to go bad.  These amps are on 24/7 and the tubes get replaced about every 18 months or so.

HTH,

Jim

[Roger A. Modjeski]

I was just looking over the Lamm website. It's impressive. I see my friend Bascom King did measurements for them. $22k is pretty steep though. There isn't that much there. Do your friends pay retail? Get them used?

[jrebman]

Roger,

Actually, they are dealers so I've been lucky enough to hear many of their components.  Yes, pricey for sure, but I suppose if you have it, it's worth it.

I will be sending you an email soon -- have a couple questions to ask and some ideas to float by you.

Any news on whether you will have any way to get some of this SES gear to RMAF?

-- Jim

[Roger A. Modjeski]

I don't plan to go this year, maybe next year. I don't mind loaning amps to speaker makers for instance.

Do your Lamm dealer friends comment on how well the gear sells? Often dealers have something for looks and to draw people in, sales are something else.

[vizion]

I found a CF SE amp (link - http://www.transcendentsound.com/cathodefollower.htm). It's not a low-mu triode or non-NFB amp I believe.

[Roger A. Modjeski]

I checked out the link. The designer doesn't understand the Futterman circuit, nor did the patent officer. The following link will take some study:  http://www.transcendentsound.com/OTLpatent.htm

For my gentle reader's question: Transcendents points out that series connected OTLs do need feedback.