You said the alternative method where output bias is measured across the emitter resistor and without the dropping resistors would give the wrong adjustments.
I would like you to explain why the alternative method will give the wrong adjustment.
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Remember that this is exactly the setup procedure recommeded for the Honey Badger in it's build guide. The HB uses 22R resistors, though. The PCB has extra holes for them, in parallel with the fuses.
Remember 1st that the Vbe multiplier acts very similar to a Zener diode with an adjustable, but basically constant voltage drop, and 2nd the voltage drop of 47 ohms times 0.06 A = 2.82 V almost is negligible, due to the drivers' and power devices' Vce/Ic characteristics.
Last but not least the good experiences others had (and probably still have) with this procedure proves it's suitability.
Nevertheless, just for convenience I'd also do it that way, as yet stated in #218.
Best regards!
Start with a lower wattage bulb.
If you are testing just the wiring of a transformer than a 28W or 40W bulb is big enough.
For a smaller pSU iusing a transformer up to about 300VA a 28W bulb is still big enough.
If you have attached you power amplifier and it draws a significant current then you will probably haveto use a 40W bulb.
If the amplifier is set up to optimal ClassA and draws 100mA to 200mA then even a 100W bulb will probably glow too brightly.
A power amplifier that draws signifiacnt current cannot be started up via a Mains Bulb Tester The filament just gets too hot and never gets a chance to cool down.
Bias setting must be done AFTER all the other wiring and construction checks have been completed and then direct on line starting for that final adjustment.
This statement of your's encourages me to ask you: Did you ever read the schematics of the amplifier in question?
Best regards!
The Vbe multiplier is a voltage regulator of the shunt style (like an adjustable Zener).
I already told you twice: you where comenting on your method while I was commenting on the resistor drop in methode.
OK, I'll try again.
You said
You said
In there you state that
Please explain why the alternative method gives the wrong adjustment.
You are deliberately mixing things up.
That is a shame because this stupid argument will cause nothing but confusion for other readers. This is why I will no longer reply to your posts on the subject.
That's not the way I see the way the Thread went.
I saw the recommend set up procedure and I gave what I think is a better set up methodology.
In the aftermath you have not been able to justify your accusation alleging that the alternative method gave the wrong adjustment.
In the light of that lack of evidence, then I contend that the better method as described in post224 is indeed the better/safer method.
Posts229 and 238 expand on the safer/better bias adjustment method and explain whyI arrived at that method. Thus avoiding the risk of thermal runaway.
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Hmmm you mean just a regular 100W household bulb (incandescent)? Surely it's not going to perform as a 100W load on the amp? I will have to search the forum to see what I've been missing out on.
EDIT: ignore me. I educated myself in the use of the bulb.
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the Mains Bulb Tester is used to check for wiring errors and major construction errors that attempt to draw large currents.
You cannot use it to set up the output bias of a ClassA, nor a ClassAB amplifier.
Start by testing the transformer wiring alone.
A dual primary and/or a dual secondary can easily be wired incorrectly. The tester allows safe Power ON without risking damage to the transformer. It even protects the mains fuse from damage in the event of an erroneous primary winding phasing.
You cannot use it to set up the output bias of a ClassA, nor a ClassAB amplifier.
Start by testing the transformer wiring alone.
A dual primary and/or a dual secondary can easily be wired incorrectly. The tester allows safe Power ON without risking damage to the transformer. It even protects the mains fuse from damage in the event of an erroneous primary winding phasing.
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Yep thanks Andrew. I need to make one of these but so little time...
I have the power supply sorted already... but it might help prevent stupid mistakes if I strip down and reassemble.
Andrew: does a GOSS band need to be connected to chassis? Or is it a standalone ring around the transformer? Cheers. .. Pops
I have the power supply sorted already... but it might help prevent stupid mistakes if I strip down and reassemble.
Andrew: does a GOSS band need to be connected to chassis? Or is it a standalone ring around the transformer? Cheers. .. Pops
A magnetic shield basically doesn't need any connection to anything. What's the construction of your transfromer? A block shaped one with Ei and similar laminations, or a C-cored one automatically will provide electric connection to it's shield, although it isn't needed. In a toroid the magnetic shield usually is within the outer insulation and cannot be connected.
Best regards!
Best regards!
Hi Kay!
It will be a toroidal transformer with electrostatic shield between windings (which I know needs a low impedance connection to the chassis ground) and also a GOSS band around the perimeter of the toroid.
What you say makes sense: if it's a magnetic shield then it should not need any earth connection(?). Thanks!
It will be a toroidal transformer with electrostatic shield between windings (which I know needs a low impedance connection to the chassis ground) and also a GOSS band around the perimeter of the toroid.
What you say makes sense: if it's a magnetic shield then it should not need any earth connection(?). Thanks!