Cheap & Well Made Chinese SE EL34 Amp

[jazbo8]

We now seem to have two threads about the same amp owned by the same person? Maybe decide which one to go with?

I was confused too... But I think they are from two different factories, even if the designs are similar/perhaps identical (if you think fake copies of foreign goods are rampant, the local Chinese copies are even worse...) But looking at the pictures, this version seems to be a bit better put together and the layout makes more sense.

Jaz

 

[DF96]

I also have a question : this design does not have negative feedback. Could someone with more experience suggest me of howto correctly do this?

Add more gain. Take it away again with feedback, ensuring that you maintain stability. You can't just slap on feedback to a circuit designed without it. If you want feedback, then you need a circuit with feedback designed in.

The circuit already has local feedback in each stage: input has both triode action feedback and cathode degeneration, and the output has UL connection.

 

[Svein_B]

As we are DIY folks here, we obviously want to change things, for possible improvement and learning.

Such as:
- add a switch to select triode, UL, or pentode mode
- apply some global feedback (amount shall depend on operating mode)

In order to add some open-loop gain to allow some global feedback, you could
- bypass 2K cathode resistor on input stage, and add another 100-200 ohm resistor below it for connecting the feedback.
- replace anode resistor with a CCS, or change input stage to SRPP.

Too bad the amp uses a PCB which make changes a little difficult, so the DIY'er may also want to convert the whole circuit to point-to-point wiring.


Had a look around and found a couple of current sources for this nice looking little amp:

www.siliconray.com/el34b-6n2j-se-tube-amplifier.html
www.goodcomponent.com/index.html