I want to rebuild the STK-0039 because I think, that is a more reliability step.
Supply voltage of Nordmende's integrated amplifier "PA1100" is only +/-32V
Maybe the BD911/912 as output stage and the BD139/140 as driver stage for getting a darlington configuration is a good solution.
For the Vbe multiplier I want to know the best solution - maybe fig. 2d on page 2 under
http://www.hagtech.com/pdf/vbe.pdf
is a proper version - a real live example that works in the right manner I have found in the Harman HK-610 integrated amplifier (go to second attachment).
But all mentioned above is the second part - first part is the check of the front-end (LTP+VAS) itself - i. e. without output buffer.
Therefore I will make this steps:
1) removing STK0039
2) between the collectors of T708 and T709 the Vbe multiplier as mentioned above
3) bypassing Vbe multiplier with 47uF electrolytic
4) shorting between the node R782-784 (power amp out) and collector either T708 or T709 (on the other collector I can check the voltage range ~1,8-3,2VDC) by adjust R13.
The right adjusted value determine later the quiescent current through the output).
As long no other fault is present, DC values and idle currents through LTP and VAS of the front-end provide same values as in normal mode with buffer stage.
The use of a tube output transformer between the output without buffer and the speakers makes even a sound check possible - with very low SPL of course.
I will report about the results in several weeks.
Supply voltage of Nordmende's integrated amplifier "PA1100" is only +/-32V
Maybe the BD911/912 as output stage and the BD139/140 as driver stage for getting a darlington configuration is a good solution.
For the Vbe multiplier I want to know the best solution - maybe fig. 2d on page 2 under
http://www.hagtech.com/pdf/vbe.pdf
is a proper version - a real live example that works in the right manner I have found in the Harman HK-610 integrated amplifier (go to second attachment).
But all mentioned above is the second part - first part is the check of the front-end (LTP+VAS) itself - i. e. without output buffer.
Therefore I will make this steps:
1) removing STK0039
2) between the collectors of T708 and T709 the Vbe multiplier as mentioned above
3) bypassing Vbe multiplier with 47uF electrolytic
4) shorting between the node R782-784 (power amp out) and collector either T708 or T709 (on the other collector I can check the voltage range ~1,8-3,2VDC) by adjust R13.
The right adjusted value determine later the quiescent current through the output).
As long no other fault is present, DC values and idle currents through LTP and VAS of the front-end provide same values as in normal mode with buffer stage.
The use of a tube output transformer between the output without buffer and the speakers makes even a sound check possible - with very low SPL of course.
I will report about the results in several weeks.
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Hello,
I just revived my Nordmende PA1100 by creating my own ST0039 replacement even mine is more similar to STK0040 (fully complimentary).
Idle current is adjusted to 25mA (11mV across Pin8 and Pin3).
My amplifier had initially jumper wires instead of emitter resistors R782 / R783 so I decided to go with 0.22 Ohm 3W.
I used darlington BDW93c/BDW94c output devices to simplify and minimize construction efforts.
Works and sounds fantastic. Posting my schematic and the ST0039 discrete replacement I built,
I just revived my Nordmende PA1100 by creating my own ST0039 replacement even mine is more similar to STK0040 (fully complimentary).
Idle current is adjusted to 25mA (11mV across Pin8 and Pin3).
My amplifier had initially jumper wires instead of emitter resistors R782 / R783 so I decided to go with 0.22 Ohm 3W.
I used darlington BDW93c/BDW94c output devices to simplify and minimize construction efforts.
Works and sounds fantastic. Posting my schematic and the ST0039 discrete replacement I built,
Attachments
Good morning!
I have been searching the web for a discrete circuit to replace a pair of STK0025's from a Technics SA-T150 receiver.
First I found in the Audiokarma forum, a topic about the STK0050, in this topic the user RCS16 presented a very well elaborated circuit, which in fact, already proven by several other users, works well and can replace several other models of STK's.
This RCS16 circuit is more complex than this circuit presented by AHTOAH (As well as the STK0050 is more complex than the STK0025).
I would like to know if anyone else implemented (real or simulated) this AHTOAH circuit, if this circuit worked well, if it had any oscillations, etc...
Best ragards, Raphael.
I have been searching the web for a discrete circuit to replace a pair of STK0025's from a Technics SA-T150 receiver.
First I found in the Audiokarma forum, a topic about the STK0050, in this topic the user RCS16 presented a very well elaborated circuit, which in fact, already proven by several other users, works well and can replace several other models of STK's.
This RCS16 circuit is more complex than this circuit presented by AHTOAH (As well as the STK0050 is more complex than the STK0025).
I would like to know if anyone else implemented (real or simulated) this AHTOAH circuit, if this circuit worked well, if it had any oscillations, etc...
Best ragards, Raphael.