2 Stage GM-70 amp in A2... possible?

[enzoastro]

I dont know if you could use the mu output from a cascoded dn2540etc with a da or other hi mu linearr triode underneath? Or perhaps the design that rod coleman uses?
Imho i think its probably not worth it for the extra db or two.
Enzo

 

[quikie22]

wokie dokie... point taken.

 

[JZatopa]

That design produces about 10W in A1... And the stacked SMPSs are a bad idea, IMHO, as the noise also adds up.


As for the JAC music schematic posted by joda above, it's a joke meant to sell a ton of expensive iron to naive people.

The noise seems to be so minor that it has little to no affect on the sound. Just check out the videos of it playing. The time of SMPS is here, if you can find the right ones.

 

[ColinA]

If god had intended us to to use S.M.P.S

He would not have invented mercury-arc rectifier valves (tubes)

J.M.H.O.

Unless you are scared to use them.

 

[Captn Dave]

In MJ third Ed page 138, he discusses using a 6SN7 or 7N7 with a CCS in place of the load resistor. This enables you to use a flat load line at say 8ma and you can swing more than 300 volts pp that way at very very low distortion. (Ed. You would need to use the other half of the triode as a first stage)

I've been considering that circuit to drive an 845. It seems better than the 300B from a cost and distortion standpoint. I've not tried it yet and don't know how well it will work.

Also, I don't know if it will drive the big triode without a cathode follower. Anyone have an opinion on that?

 

[enzoastro]

Mu followers seem to be a four letter word these days, but if you have 1000+v to play with, need a flat load line and low driving impeadence they seem to fit the bill to me. i use one in my gm70, 6e5p for both load and gain stages with a 25w 15k vishay bulk foil as the load and 22.5ma/180v. b+ is regulated 700v (dont suppose it needs to be) down from 930 for the outputs, sounds pretty good to me, though i intend to try different gain valves and topoligys in the future.
I hope to put some measurements together over christmas.

enzo

 

[JoshK]

Haven't analyzed the 211 vs GM70 close enough to know if they require different drive, but on the surface they are similar.

https://lh3.googleusercontent.com/-...AAJo/-bS8dYrJIdU/s1600/SE211-6HS5-PSUincl.jpg

Thomas says he gets a bit of class A2 from the 211 and that is 2 stages san SMPS.

 

[dgta]

Was wondering if a 2 stage amplifier would be able to achieve A2. Any ideas?

Sure. If this was a question on an exam, with no other specs attached, I would say no problem. I will define the input requirements so I can easily achieve that.

If you're actually trying to design something, then the answer is "depends". You need to specify the input to be used and the definition of "stage". And any other restrictions you want to place on it, like how far into A2 are we talking? How much distortion, etc.