Hi I have to repair BAD homemade amplifier..
a Chinese board was used, there is a scratch to the up and down of the volume,.. on left and on right obviously the potentiometer are changed, and one of channels has the transistor that don't work fine it has a very low gain.
When I detected it with a tester components, is see it as a resistance, while when measured with the multimeter it corresponds to an NPN transistor but also results in a resistance in the two terminals,
the test with multimeter.... The collector is in the middle..
The audio signal is the yellow wire, and the out of the transistor go to pin 8 of the tube.. on a cathode, then low impedance.
Someone knows something ?? Someone know some reference ? Schematic ?? Transistor kind ?
Thank you for now
a Chinese board was used, there is a scratch to the up and down of the volume,.. on left and on right obviously the potentiometer are changed, and one of channels has the transistor that don't work fine it has a very low gain.
When I detected it with a tester components, is see it as a resistance, while when measured with the multimeter it corresponds to an NPN transistor but also results in a resistance in the two terminals,
the test with multimeter.... The collector is in the middle..
The audio signal is the yellow wire, and the out of the transistor go to pin 8 of the tube.. on a cathode, then low impedance.
Someone knows something ?? Someone know some reference ? Schematic ?? Transistor kind ?
Thank you for now
I have detected the electrical diagram, for me very strange
I don't understand what kind of component it could be that looks like a transistor but has no power supply.... how can it amplify??
I bypassed the "transistor" with a 1000 ohm resistor but you can still hear the rattling of the volume potentiometer, and there is very little power output to the speakers. In red the voltage measured
I don't understand what kind of component it could be that looks like a transistor but has no power supply.... how can it amplify??
I bypassed the "transistor" with a 1000 ohm resistor but you can still hear the rattling of the volume potentiometer, and there is very little power output to the speakers. In red the voltage measured
WOW OK .. well but this is the first step.. I had never seen this setup without polarization
but the fet not work fine.. and there is the noise during turn up and down the volume.. on a cathode there are only 2.5 volt...
but the fet not work fine.. and there is the noise during turn up and down the volume.. on a cathode there are only 2.5 volt...
Perfect.. good work ! Thank you Hooman you are an expert ...
In your opinion, what could be the reason for hearing the noise when adjusting the volume potentiometer?
this is the first problem.. in this video you can see and hear the scratch
I don't know what type of fet is mounted I have order a pair of 2SK170 I think that it is good for low audio signal..
In your opinion, what could be the reason for hearing the noise when adjusting the volume potentiometer?
this is the first problem.. in this video you can see and hear the scratch
I don't know what type of fet is mounted I have order a pair of 2SK170 I think that it is good for low audio signal..
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Dear Hooman more strange for me...
the DC noise is disappear.. but with 100 nF as you described
1000 Hz on the catode the Triode PIN 8 there is a abnormal signal "Yellow trace" and on the speaker "Blue Trace" the signal is very low..
the same signal same volume withoud capacitor it is normal
----------------WITHOUT CAPACITOR ----------------------------------------------------------------- WITH CAPACITOR
the DC noise is disappear.. but with 100 nF as you described
1000 Hz on the catode the Triode PIN 8 there is a abnormal signal "Yellow trace" and on the speaker "Blue Trace" the signal is very low..
the same signal same volume withoud capacitor it is normal
----------------WITHOUT CAPACITOR ----------------------------------------------------------------- WITH CAPACITOR
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Tube circuits are simple but sometimes complicated by errors. You have to work on them.please chaneg cap to to 1 mfd or .47 mfd....and test ?The transistor may be a regular bipolar transistor. Can you send the picture below of pcb?
I tryed with the FET 2sk170 and it work fine.. I don't know the listening normal power, but I think that is good.. without cap
there is the same noise.. but the problem with capacitor is after the fet.. the signal naturally passes through the cap
the signal is present on the gate of FET after the fet there isn't
Also with 470 nF or 1 uF the result it the same.. change the waveform the better is as 470nF but there is a minimal signal out of speaker..
the waweform change also during volume pot moving up and down.. it is very strange..
the below of PCB is this..
In the first video with 0.47 uf and without cap in the second .. same input signal same range. In blue signal in yellow on the cathode of tube.
there is the same noise.. but the problem with capacitor is after the fet.. the signal naturally passes through the cap
the signal is present on the gate of FET after the fet there isn't
Also with 470 nF or 1 uF the result it the same.. change the waveform the better is as 470nF but there is a minimal signal out of speaker..
the waweform change also during volume pot moving up and down.. it is very strange..
the below of PCB is this..
In the first video with 0.47 uf and without cap in the second .. same input signal same range. In blue signal in yellow on the cathode of tube.
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This circuit is a completely professional . Increase the 3.9k of pin 1.... 2,4 v is too low . and reduce the 47mfd capacitor .
For
Because the problem is that I must desoldering tube for to see below change value resolder the tube and try..
the assembly is very bad.. the socket of tube is on top of the chassis ...
Yes sorry..
For example.. that value do you think correct 8.2 K ?? And capacitor ? 22 uF ??
Because the problem is that I must desoldering tube for to see below change value resolder the tube and try..
the assembly is very bad.. the socket of tube is on top of the chassis ...