Electronics > Beginners
Trimpot rating when in place of two resistors??
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schmitt trigger:

--- Quote from: Ian.M on February 12, 2019, 11:56:38 pm ---OOPS!  |O  I missed some flyspeck decimal points in front of the emitter resistor values.  I dislike schematics that don't follow the convention of replacing the decimal point with the S.I. multiplier letter, (with R for unit ohms) and *HATE* ones that use decimal points without a leading zero.


--- End quote ---
:-+
Same feeling here.
Even though most schematics are nowadays CAD drawn, and therefore any distributed copies will faithfully preserve all details, there will be the time when the schematic will be printed on a low-toner printer, and similar mistakes will happen.
Ian.M:
Those instructions say its meant to run in class A with 1V between the output transistor emitters.  That corresponds to 735mA per output complimentary pair, and a total quiescent current of 1.47A.  In practice 10% either way should be acceptable.

I'd suggest checking the current source by measuring the voltage across R10 - it should be 0.6V for 6mA current, and checking that all the resistors in the Vbe multiplier and output stage are as per original design, with *NO* potentiometer then following the published instructions from 'Final Tests' on page 6 onwards.   

If you need to mod it for class AB operation because its heating your room too much in the summer, do the tests I described in reply #15 and report back here.  You'll probably have to increase C3.  I wouldn't recommend pure class B, but you could certainly trim it down to only a few watts quiescent dissipation in the output stage.
Robbie010:

--- Quote from: Ian.M on February 13, 2019, 08:03:53 pm ---Those instructions say its meant to run in class A with 1V between the output transistor emitters.  That corresponds to 735mA per output complimentary pair, and a total quiescent current of 1.47A.  In practice 10% either way should be acceptable.

I'd suggest checking the current source by measuring the voltage across R10 - it should be 0.6V for 6mA current, and checking that all the resistors in the Vbe multiplier and output stage are as per original design, with *NO* potentiometer then following the published instructions from 'Final Tests' on page 6 onwards.   

If you need to mod it for class AB operation because its heating your room too much in the summer, do the tests I described in reply #15 and report back here.  You'll probably have to increase C3.  I wouldn't recommend pure class B, but you could certainly trim it down to only a few watts quiescent dissipation in the output stage.

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Thanks Ian.

I did read in an other forum that the design of the circuit can be altered to A/B rather than pure Class A, so I assume that is why the original builder of the amp installed the trimpot. I have no interest in that so will convert it back to standard as per your advice.
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