Problem with old vintage russian amplifier мощности п70
Problem with old vintage russian amplifier мощности п70
Helo,guys ! In attached diagram I have following problems:
1. Channel no.1 is working well , no.2 is overloaded (huge idle current with R76, R77,R82 factory setting). R82 is variable resistor, not fixed.
2. All 3 T18 pins have 39V
3.T18 pulled out and checked - ok
4. T18 back onboard, wire 23 and 25 disconnected - still 39V all 3 pins
5. Both channels will smoke R77 or R31 if adjusted nearby their end.
6. All T16,T17,T19,T18,T20 checked, all ok.
Did'n ckecked T19 and T20 connections, maybe mixed by some guy , T19 and T20 are previously replaced by KT 809 by other hands.
Did'n ckecked T15 and ahead.
Thks in advance.
Problem with old vintage russian amplifier мощности п70
Helo,guys ! In attached diagram I have following problems:
1. Channel no.1 is working well , no.2 is overloaded (huge idle current with R76, R77,R82 factory setting). R82 is variable resistor, not fixed.
2. All 3 T18 pins have 39V
3.T18 pulled out and checked - ok
4. T18 back onboard, wire 23 and 25 disconnected - still 39V all 3 pins
5. Both channels will smoke R77 or R31 if adjusted nearby their end.
6. All T16,T17,T19,T18,T20 checked, all ok.
Did'n ckecked T19 and T20 connections, maybe mixed by some guy , T19 and T20 are previously replaced by KT 809 by other hands.
Did'n ckecked T15 and ahead.
Thks in advance.
Attachments
The classical quasi-complementary Lin circuit. 5 transistors are directly connected. R34/77 setting the midpoint 19v, the quiescent current R37 / 82 is selected. Check for damage to T16. Diode D2 in the collector. Poor soldering. Replace capacitors K50-6 .
Pinout of transistors. Check transitions like diodes.
R31/76 Common NFB from the output (constant voltage 20V). Set trimmer to maximum resistance (minimum NFB).
Check the 1ohm resistors in the emitters of the output transistors R84,86\ 85,87
Pinout of transistors. Check transitions like diodes.
R31/76 Common NFB from the output (constant voltage 20V). Set trimmer to maximum resistance (minimum NFB).
Check the 1ohm resistors in the emitters of the output transistors R84,86\ 85,87
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