Bewitch KT88

[SONDEKNZ]

@saltonm73
Yes. My mistake. Both the resistors under discussion are 100R. My bad.

I will take some time to unravel what you have explained above, as I am self-taught - and this is a bit puzzling.

Thanks for making the effort to help me understand what this circuit really looks like.

PS: German AND English... impressive! 😊

 

[saltonm73]

I am attaching a plan of the Bewitch 6550/KT88 that I just created, of various transformers from which the input and output voltages of the transformer can be seen on pins.

 

[SONDEKNZ]

@saltonm73

BRAVO! Appreciated. 😎👍

 

[SONDEKNZ]

Hello SONDEKNZ

I have to praise you for the amount of time you have invested so far and for being so keen to experiment with trying out different circuit variations and always listening to which one sounds better for you.

I have also spent the last few years improving my Bewitch 6550, both externally and internally, and also changing the circuit diagram.

I have stuck with a circuit variant based on Lampizator and will stick with it, and will not continue to look for or configure other 6550/KT88 solutions.

With our beloved BEWITCH 6550/KT88 push-pull integrated amplifier, I was always dissatisfied with how the schematic was configured and released from the factory. Recently I took the time and effort to sit in front of the PC again and looked for improvements to the circuit diagram, making changes to how the circuit board really is and changing them, and this is what the circuit looks like.
View attachment 1359187

There are still a few errors on your circuit diagram and there is still room for improvement. There are still some resistors there, namely R17-R18-R19 and R20 with 100K in the power supply area, which don't actually exist on the circuit board.
Also at another point on the transformer secondary 6.3v/2A this output leads not only for the
preamp tubes
V1-V2 (6N8P) tube heater, but also the two connected resistors R23 -R24 with 100 Ohm with point A noted that the two tubes on this heating winding are increased to 42 VDC, which has a common bias voltage of only two 6550 tubes of one channel

View attachment 1359188

I also find that with several capacitors that show incorrect values, instead of the 33uF/400v, a value of 22uF/400v is given on the schematic.

Please check and change on the circuit diagram if possible, unless at the places where I noted with X or circled on the circuit diagram, the components are there or you soldered them in later, then it is something different.
At least if we show schematics here for other forum users, it is also desirable and beneficial if they can find a correct schematic.

@saltonm73

I have found a bit of time to revisit this schematic.

Above, you suggest that the 4 x 100R resistors do not exist on the circuit board.

However, I suspect that the two 100R resistors shown in the image below, are 2 of the 4.

Therefore, the PSU side of the schematic looks to have 2 x 100R resistors, NOT 4.

I have not yet been able to check the amp to confirm which 2 x 100R PSU resistors need to remain in the previous schematic, but I suspect it is R19 and R20.

What do you say?

 

[saltonm73]

Hello SONDEKNZ

That's exactly how it is, the 4 x 100K resistors are not on the board.

To clarify again, the 4 x 100k (please do not confuse with 100R) resistors R17-R18-R19 and R20 are not on the board.

If the resistors were actually on the board as per the factory circuit diagram, then the resistors would also have been placed directly next to the 4x capacitors C5-C6-C7 and C8 either from above or from below, but they are not.

I have drawn on the picture where the resistors would be on the boards.

 

[SONDEKNZ]

@saltonm73

Thanks for sticking with me on this.
Okay. I guess I am clutching at straws here, trying to work this out from photos and schematics.
I'll need to wait until the next time I pull the whole amp down and try to trace through the PCB, and finalise the true schematic once and for all.
It WILL eventually happen... 😊