What determines whether a tube amp needs negative feedback or not?

[tardishead]

Provided that the input and output transformers have good frequency ranges what determines whether a tube amp needs negative feedback or not? Can we start with a simple cathode biased single ended triode output design?

Can someone point me to some good reading on the matter?

 

[alexc]

Negative feedback generally trades gain for lower distortion, lower output impedance and extended gain-bandwidth as
well as to ensure the amp operates with stability  ie. no oscillation or crazy phase shifts

http://en.wikipedia.org/wiki/Negative_feedback_amplifier

So what determines the need for it is the desired specification for distortion performance, output impedance, phase shift,
gain-bandwidth and stability into specified loads.

Cheers

 

[tardishead]

What exactly determines the bandwidth in a simple 2 stage single ended amplifier?

Input and output transformer
Coupling capacitor between stages.

Am I missing anything??

 

[alexc]

Assuming no feedback/phase compensating network, what you mention plus
inherent tube effects, like Miller capacitance.

And the interaction of the above with each other and the various resistances around the circuit.

Working thru design examples of SE circuits would help. I would start with a single stage then expand to a 2 stage.
There should be some google examples of grounded cathode amps out there that show the formulae for calculating
capacitances, resistors and so on for desired bandwidth.

Calculating phase compensation networks using negative feedback to guarrantee stability gets more complex.

Maybe PRR can shed some light in his concise, entertaining and to the point fashion  ;D