BGW 750C find the right military resistor ???

[bonesbiggis]

Hi

Have to know resistor code and value of R22 in a BGW 750c

On right channel i got a RN60/78ohm
on the left channel it was no one

In the attached file some one have written down R22 is a RN65 / 75ohm is this true ??

if some one know the original value and code of R22 plz let me know!

Can some one who got one BGW 750C that dont have bean tutched maby take it apart and look ?

tnx with kind regards

 

[Goldie99]

I don't know the amp, but R22 is part of the Q3 vbe multiplier that determines the bias current of the output stage, so is critical to the correct operation of the amp. I'd suggest not to mess with it unless absolutely necessary; the actual Ohm value of R22 used is chosen to set the required bias, as shown in the relevant manual (the same page as your schematic is copied from), so it would not necessarily be the same between different amps...

If you need the manuals, they're on the hifi engine or elektrotanya websites.

 

[bonesbiggis]

to measure bias 370mV emitter resistor for Q10/Q11. I dont understand where to put the probes is it across R 37 ?

 

[Goldie99]

R36 & R37 are the emitter resistors of Q10 & Q11 respectively, so to measure bias you'd normally put one probe each side of R36 OR each side of R37, according to the schematic page.

Note - you cannot measure bias if there's no resistor in the R22 location, as your first post seems to suggest. If that's the case, then the amp has probably suffered some kind of failure and is likely to need a lot more than just a new R22... impossible to say without a lot more information.

 

[bonesbiggis]

can i use a traditional potentiometer instated of a military resistor to find the right value ?

 

[Goldie99]

Assuming the rest of the channel is undamaged, then that seems like a reasonable approach, and the corresponding R22 in the other channel should give you a starting point value / range.

I'd also strongly recommend using some form of current limiting as/when you need to power the amp - but make final bias adjustments on full supply, before then replacing the pot with the relevant fixed resistance (for reliability).

 

[jheu02]

Does the amp not have any pot for bias adjustment? I've swapped in trimmers to adjust DC Offset and then replaced them with the closest fixed value R I have on hand.