[Wumpi]

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

[Dillen]

Mark-sf wrote:

The 250-ohm trimmer and TR45 governs how much no load bias is applied to each base. It is mounted on the heat sink to sense temperature and also adjust the bias. It’s possible that transister is bad or the adjustment is too high. The circuit calls for a BC311 and since the bias is not separately adjustable for its BC310 mate its possible that your BC161 is a poor match. Sorry, but its been too many years since I worked on one of these.

TR45 is usually a small BC183 or such.
TR44/47 does not have to be matched, as they see the same current flow regardless (more or less – in a working circuit).
Even the output transistors doesn’t have to be exactly matched, really.
The above also goes for them, and their emitter resistors will compensate a little for minor differences in hFe as well.

But the problem in this case is of a different scale.
A DC reading in a “controlled” environment (variac and a couple of multimeters) on the output rail would tell something. As would DC-readings
on the driver transistors.

Replacing components just to see if they burn, will not help in any way.
You need to find out what is really going on.

Martin

[Dillen]

Wumpi wrote:

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

Sounds right. But the idle current is not the problem in your case.
You will have to find and correct the problem first.

Martin

[Wumpi]

The output voltage on the resistor is around 28v

So 28÷0.15=186

Are you sure this the right proccess?

[Dillen]

The idle current should be expected to be around 7,5-15mV or something within that range.
The service manual will specify what’s correct for your model.
But the idle current is not the primary problem in your amplifier. If it’s wrong, it’s because something else is amiss.

Which resistor are you measuring across?

Martin

[Wumpi]

R491 output

Btw which capacitors output stage are you referring?

Thanks

[Dillen]

28V across R491? That resistor is no more.

I am referring to all electrolytic capacitors in the output stage, and also in the preamp for that matter.
= All electrolytics on the board.

Martin

[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.

 

 

[Dillen]

Since this is a single-supply amplifier, apprx 50% of VCC is to be expected on the output rail – with respect to ground.
(Hence the need for an output series capacitor).

Martin

[Ninni]

The idle current should be measured by unplugging the supply lead to the power amplifier for the channel to be measured and inserting an ammeter in between. This should read 100 mA, if I recall correctly. There is a warm-up time for taking the reading. Everything is in the service manual.

[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

 

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