Listen. I have problems with my eyes and I have no more equipment except an old Unaohm and a home-made signal generator.
If you want to try to build it here is the .asc file. The coil on Gs is essential. Diodes D1 and D2 must be bridge rectifiers. The 27 1N4148 series is to be tried instead of the Rk 270ohm. However, some values should be adjusted based on the type of output transformer used, but it is the starting point.
I do not take responsibility for construction failure.
Last edited:
Thx but it is not my interest now.
I have a lot of stuff to use for Schade config, in case.
But it is interesting that it is difficult to see some real test on lab of this config.
Walter
waltube
The idea behind this modification of the original circuit is very simple: by adjusting the ratio of the resistor values R 1 vs R 2 (R 1` vs R 2`) both first grids are brought to 0-Vdc potential, and in the same way the value of the local negative reaction from the anodes of the output lamps to the first grids is also adjusted at the same time.
ps, The advantage is that there are no more capacitors connected in series with resistors R 2, but there must be another negative voltage source, in this case it is a -300V source.
The idea behind this modification of the original circuit is very simple: by adjusting the ratio of the resistor values R 1 vs R 2 (R 1` vs R 2`) both first grids are brought to 0-Vdc potential, and in the same way the value of the local negative reaction from the anodes of the output lamps to the first grids is also adjusted at the same time.
ps, The advantage is that there are no more capacitors connected in series with resistors R 2, but there must be another negative voltage source, in this case it is a -300V source.
Last edited:
I noted now the value you put on circuit.
But I think is necessary to test on desk.
And seems to be little complicated including the trafo
Walter
If you mean a small driver transformer then IMHO it's not that complicated because no DC component flows through the secondary windings as long as such an output power stage operates in A1 or AB1 class, but as drawn there is certainly a DC component flowing on the primary side of the driver transformer.
No. Not this point , it is evident that no DC is present
I think the setting of a proper % of FB will be checked on desk to reach the best performance
Agree
In the my test with different setting I see the enormeous changing in the results.
These are, in final, scarce respect the standard type of FB normally used.
The funny thing is that seems is very difficult to see some complete test lab of a real circuit, s.e. or p-p, to understand what happen .
I am moving now on p-p config after the s.e. , taking some example seen in the forum ; I am happy because there are lot of iron at my disposition so I hope to see something interesting ( but I have a great doubt)
Walter
RCA in their handbook published very interesting push-pull amp schematic, with local feedback around output tubes, and around drivers: to anode and cathode of the driver. Perfect approach. I use something similar in my amps.
After I get the amp that I am working on completed, I am going to redesign my Unity-Coupled amp so that it consists of two stages only, a CCS-loaded pentode input stage and the output stage. I'll take feedback from the cathodes of the output tubes to the cathodes of the input tubes. It'll be my first nested feedback amp.
My current project is also 2 stages and ~36dB of feedback from output tube plate to input tube cathode. It's a lot of feedback in one loop. I can't provoke any bad behavior but I don't know how much phase margin I have. Unity-gain bandwidth is ~17MHz, though, which scares me a bit. That was in bench testing and as I build I will have to adjust for the new phase response of the new layout.
But it is a lot of FB.
In my opinion the best way is to fix a minimum of performances in open loop then apply a low % of Fb to reach a reasonable value of THD, FFT spectrum, response.