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Another emitter resister change question....

Nashou66

Nashou66

AK Subscriber
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I have a Sansui 5700 that has an open .33 ohm dual emitter resistor .
I am waiting for some to be delivered but it seems the eBay seller is slow to ship. :whip:

So I have parts amp that has .22 ohm dual emitter resisters and want to know If i could use those till the correct value come in. I was reading that the bias would need to change and I could use the new value if I got the new correct bias value.

So with the .33 ohm R's the bias is to be set at 3.3mV . using ohms Law I came up with a .1mA current if I did that correctly.

So with a .22 ohm and using the 3.3mV I get .15mA , so here is the question, what is the new bias voltage beset at? 3.3mV is what it should be with .33 ohm,So what should the mV be with the .22 ohm ? N to sure what values to use in the formula .1mA or the 1.5 mA .

Athanasios
 
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To get 10ma with the .22Ω resistor .. Bias needs to be adjusted to 2.2 mv.. ( across one emitter resistor )
 
Now when adjusting the bias by the manual on the Sansui. Are you measuring across one emitter resistor or two ?
 
avionic said:
Need to recalc for two emitter resistors.
To get .010 A with .22
R1 + R2 = .44
.44 X .010 = 4.4 mv
Click to expand...
Here is the Correction to the main manual , maybe its one half the resistor?

53024947066_30b4db63fa_b.jpg
 
You're only measuring across 1/2 the emitter resistor package according to the schematic, so it's one emitter resistor you'e measuring across, even though there are two in the package. So (of course) avionic is correct.
 
You could measure across BOTH resistors, but you would need to DOUBLE the voltage you are expecting, from 3.3mV (for one resistor) to 6.6mV for two resistors. The reason they tell you to measure across ONE resistor is because the terminals for one resistor are likely available at the board edge at pins 03 & 04 - which should make locating the measurement points very easy. ;)

Of course! :p
 
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I'd use 2x0.33ohm individual resistors rather than the 0.22ohm duals, the 0.33ohms should be easy to source...
 
mbz said:
I'd use 2x0.33ohm individual resistors rather than the 0.22ohm duals, the 0.33ohms should be easy to source...
Click to expand...
This is the board they go on, the resistor kinda touched the heat sink . If there is stability while testing I think it will stay. Not sure when the .33 duals will arrive ....if ever. Also I don't feel like ordering just for this. I removed 8 of the .22 duals from a parts Yamaha AVR . So I might as well use them.

53025119222_9babc5013c_b.jpg




Now another question, if the .22 ohmmer's work and there is no thermal runaway or the likes, should I replace the .33's and adjust bias to for the .22's as well?


Not even sure if anything else is wrong with this amp, it had two blown outputs along with one half the emitter. Im going to use a resistor inlace of the outputs on that channel and see how it behaves on the DBT.

Athanasios
 
Ok used 490 ohm 1 watt resters across the removed outputs E and B and got sane reading on DBT. Moved it to full power and relay clicked and voltages seam reasonable. Going to put the outboards back onto heat sink and install the replacement output tranny's and see if I can adjust bias etc.

Athanasios
 
Ok fired it up but the DBT was pulsing, figured it was the Bias not being adjusted correctly,So I turned the one VR on the repaired channel and it adjust a little then it would go wonky!!

So I pulled the VR-04 and this is what I found.

53026319540_fa2cf5324e_b.jpg



Looks like it melted !!!! Never seen that before!!!

Put a new 100 ohm multi turn bourns in and dined it to 2.2mV and the amp works fine !


So far so good !


Athanasios
 
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Kinda looks soldering iron induced..Does it ohm out 100Ω end to end ?
 
avionic said:
Kinda looks soldering iron induced..Does it ohm out 100Ω end to end ?
Click to expand...

No it read nothing, actually on my cheap Chinese tester two of the pins read about 30 pf and the others had OL . It definitely got fried , I can see it burnt inside I think.

EDIT: also nothing around that part looks like it was replaced, it all looked original from the factory.
 
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