Make a class AB tube amplifier lean more towards "A"

[aardvarkash10]

Other than copying his circuit exactly, whatever else I'd build would probably just turn into an oscillator. Hence the sticks 'n stones approach I initially suggested.

The advantage of the local shunt feedback (commonly and contentiously referred to as Schade feedback) is that you are very unlikely to get into an oscillation situation - there is just not enough phase shift available.

 

[DF96]

I'm making an assumption that compromises have been made in the stock form that allows the product to cover as wide a range of application as possible. And, these compromises can be exploited to improve some aspect for a specific use case.

That can sometimes be true, but it needs careful reverse engineering to identify a compromise and undo it. Does not apply to amplifier Class in the way that you think.

Maybe in the last 20 years it's all been concisely worked out

No, much earlier than that. Understanding amplifier classes goes back at least 90 years.

Say the OEM says to bias the amp at 40 ma, each tube. You take a DMM and measure the voltage across the tube and find its 425V. You assume the 10K or so tube resistance matches up well with the output transformer's primary winding and that this bias setting is optimal for transferring power through the transformer into an 8 ohm load.

No, it is not as simple as that. You are confusing DC resistance with AC resistance with optimum loading: three different concepts.

 

[Chris Hornbeck]

I think a lot of the confusion around this topic comes from unawareness of plate curves, and of what they mean. It's covered pretty well, including real, old-fashioned graphical analysis, in Radiotron (RDH4), but they're hard to come by, and their 1950's design goals are IMO wrong for modern DIY builders.

Does anybody know of a good website presentation that we could all recommend to folks just getting into the topic?

All good fortune,
Chris

 

[aardvarkash10]

Does anybody know of a good website presentation that we could all recommend to folks just getting into the topic?

All good fortune,
Chris

I've always found Merlin's stuff very helpful - graphical analysis for dummies.

 

[Celsius]

Always I thought that best pp with DHT is to have all possible class A, and the extra power are available when entry in A2 and class B respectively, with more class B have NFB is mandatory. My thinks are right ?