Looking for a 300b SE design

[ZackPlonk]

What I thought might be a good reason for looking at direct (DC) coupling between driver and output stages in the particular case of a 300B amp might be the fact that we require a rather large voltage swing into the output tage. So slew-rate requirements between driver and output tube are bigger.
Furthrmore, since the output power is a bit limited, we would be pushing the amp into the upper regions more often as compared to higher powered amp. Consequently, good overload recovery would be an important design goal.
My understanding is that direct coupling of the output tube can. help with both of these aspects.

 

[euro21]

Can you tell how much the distortions are ?

Measuring at 2013:
6W, 9W.

 

[popa marius]

Thanks, very nice harmonic spectrum and low distortion I'm sure your amplifier sound great

 

[stephe]

Measuring at 2013:
6W, 9W.

Are these measured from an actual amp or simulation? Just curious.

 

[euro21]

Measured (VT-176 dual channel voltmeter, EMU0404 USB, Visual Analyser).

 

[popa marius]

This is driver for the Electro Harmhttps://postimg.cc/BPW5JNg7onix 300b tube

 

[stephe]

Measuring at 2013:
6W, 9W.

Measured (VT-176 dual channel voltmeter, EMU0404 USB, Visual Analyser).

Cool thanks. I see so many posted simulations, it's nice to see an actual >measured from a real live amplifier< one

 

[euro21]

It was the best (low THD) pair of 300B (gold grid EH300B) which I have for decades. Sadly one of them died (filament interrupted) after few years.
Nowadays the SQ is much worse, so it's probably unrepeatable.

 

[Bernie88]

Too bad for you, Euro21. Why not buying one of the new WE 300B tubes instead?
Will they sound not good enough compared to those gold grid replica tubes?
Just asking for curiosity as I'm not into the 300B game any longer..its only for the rich kids.

 

[stephe]

It was the best (low THD) pair of 300B (gold grid EH300B) which I have for decades. Sadly one of them died (filament interrupted) after few years.
Nowadays the SQ is much worse, so it's probably unrepeatable.

Yeah I noticed a big difference between the Psvane and the 300B-z tubes.

 

[euro21]

Why not buying one of the new WE 300B tubes instead?

None of all 300B type suitable for A2.
Most of them reacts with growing distortion if grid swing approaching or exceeding 0V.
Robust metal anode and grid wire types (for example old ValveArt, Electro-Harmonix or JJ) can be used.

I'm not sure, that "boutique" production tube (NOS or replica WE, Elrog, EML etc.) worth it for testing.... as you can say it's only for rich kids.

 

[waltube]

to euro21
your schematic is a dc coupling to 300B?


Walter

 

[Bernie88]

With triodes, using an excellent IT is most often the better way for achieving maximum signal quality. Especially as driver for a precious 300B boutique tube. Nobody wan't to harm this.

 

[euro21]

to euro21
your schematic is a dc coupling to 300B? Walter

Yes, the source follower DC coupled to power tube.

 

[agent.5]

I will try this one myself someday

Direct coupled SET proposal – wauwatosa tube factory

I will order and use Rod Coleman's new shunt cascode kit. I'm not sure if it is ready yet or not.

 

[waltube]

to Agent
how can call it a tube amplifier?

Walter

 

[agent.5]

because it has tubes and output transformers. I also have interstage transformers amps. I guess that I just don't care about tube purity anymore.

 

[popa marius]

I resend the picture with the driver designed, i hope the picture is correct this time

 

[audiohead]

Popa Marius:

Have you actually built this driver circuit you posted?

Is the Vout 70v rms, peak or peak to peak?

THD+N figure posted is measured at what output level?

Is the THD+N figure shown on the schematic measured value or simulated?

Art

 

[audiohead]

This is basically Alan Kimmel Fig.4 Mu follower circuit.

http://www.fetaudio.com/wp-content/uploads/2003/09/Mu-Stage.pdf


Art