[Wumpi]

I am getting back in this forum cause this amplifier makes me crazy.

Tr 47 keeps blowing all the time.i have checked the voltage and its all good

The trimmer pot is working fine after i desoldered it and check it out.

It’s on middle position set..

What should i check to find out the problem?

Please guide me..

Thanks

 

[Wumpi]

Hello Dilen

Thanks for the information.

Btw the left channel in stage 3 amplifier the supply voltage is way down than the normal voltage.It is around 15 volt

Although the rail voltage is 60 volt in tr57 for example all the voltages are around 16

Tr58 collector is 17 volt.Tr62 base is 15v Tr 61 collector 16v

I have checked the resistors and there are all fine.I have isolated output amplifier transistors nothing changes.I ve changed 558 553 capacitor still the same

I moves the trimmer pot few clicks behind and forward with no result

Btw The trimmer works

I get output signal in speaker but the voltages are not correct..

[Wumpi]

So when adjusting the bias voltage,in the beginning the trimmer should be full counter clockwise right?

Thanks.

[Wumpi]

No i was reffering in the output only .so I will meausure across the resistor and with that value I will apply the ohms law.

Is it worth upgrading this receiver?

I have also philips 22rh 720 class a upgraded..

Thanks for your technical support.

 

 

[Wumpi]

R491 output

Btw which capacitors output stage are you referring?

Thanks

[Wumpi]

The output voltage on the resistor is around 28v

So 28÷0.15=186

Are you sure this the right proccess?

[Wumpi]

So shoul i measure volt from the resistor from tr49 emmiter and with ohm law to adjust the current?

[Wumpi]

Hello.

Which emmiter resistors are you referring?

No I didn’t replace the output capacitors.

The manual aI read doesn’t refer anything about bias procces setting.Not either any mv number set.I replaced tr47 bc311 with bc 161.But the base voltage would come around 27 volt as I remember.

[Wumpi]

But Bc 161 specs are almost identical with bc 311.

Btw How many miliampere should I adjust?

The manual doesn’t say anything for the adjustment.

In which transistor base should I put the multimeter probes to take meausurement?

Thanks

 

[Wumpi]

How much the bias should be set?where exactly should I look?

The problem is that the replacement transistor burned again after a few minutes..

[Wumpi]

Finally I fix.

It seems that tr47 was damaged and from the swap proccess from left channel I accidentally put the same transistor..

I replacced it with bc161.

Now i must set the correct supply voltage.

The base voltage in right channel is 27.5 and left is 22.2

Thanks for your support

[Wumpi]

Anode right channel 568 kohm.

Left channel 590kohm

[Wumpi]

Exactly it’s 0 volt on two transistors as you describe..I check the traces and everything is fine.i will make the meausurement on diode tomorrow to see the results

Btw I tried to put voltage from base of tr46 on tr47 and i read 3 volt on collector of tr50.Without this voltage the collector goes around 29v.

Why is this drop assuming that the base should have this voltage?

THANKS

[Wumpi]

Hello.

Thanks for your interesting.

There is no voltage on anode leg of diode.i swapped two times with new but still nothing.

The trace is ok

I did a bridge between input and output of diode and I measured a significant voltage drop on the collector of tr50.Without the jumper the voltage was around 28 volt.

With jumper it went to 5 volt!!

Base volt was exactly 0.5volt

Any thoughts on that?

 

[Wumpi]

Hello Mark.

The voltage in left good channel is around 22 on input diode and on right is 27 voltage.more close to factory.

BUT this transistors are only for current protection. As the manual says.When I removed them the left channel had still voltage on diode output.

Btw base voltage 28.6 emmiter 29 collector 0

 

 

[Wumpi]

It’s not tr46 cause I swapped from the left channel and still nothing..

The commiter still has no output voltage while base and emmiter has..

[Author]

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