This is after the first channel seemed to bias up properly? At full bias the bulb tester will remain bright. Did you disconnect the first channel from power when you tried the second?
If you are at the initial test phase on a single channel and haven't turned up the bias, I'd turn off and then verify that the bias pots are set to as close to zero as possible. If that is correct, check that you haven't reversed the positions of the output devices.
If you are at the initial test phase on a single channel and haven't turned up the bias, I'd turn off and then verify that the bias pots are set to as close to zero as possible. If that is correct, check that you haven't reversed the positions of the output devices.
Does this mean that on a full blown V3 able to give 100W /Channel Class A into 8 ohms the diodes will come into play only when the demand is greater than 100W?
no.
The diodes start conducting @ around 400mVf.
They will be fully conducting by 600mVf.
For 0r47 Source Resistors that means starting to conduct @ ~850mA
Fully conducting when passing ~1.5A
A 3pr output stage would thus pass ~4.5Apk, most of which will go through the load.
4.5Apk into 8r0 is equivalent to 81W
A 100W into 8ohms ClassA amplifier will be biased to ~2.6A
That amplifier will still be in ClassA when output current has reached ~5.1Apk
If the diodes are being heated by the output devices, then they will come on at a lower Vf, maybe around 350mVf to 380mVf.
Again a 3pr output stage will need to pass just 2.4A (for 380mVf) to bring the diodes into play.
The diodes start conducting @ around 400mVf.
They will be fully conducting by 600mVf.
For 0r47 Source Resistors that means starting to conduct @ ~850mA
Fully conducting when passing ~1.5A
A 3pr output stage would thus pass ~4.5Apk, most of which will go through the load.
4.5Apk into 8r0 is equivalent to 81W
A 100W into 8ohms ClassA amplifier will be biased to ~2.6A
That amplifier will still be in ClassA when output current has reached ~5.1Apk
If the diodes are being heated by the output devices, then they will come on at a lower Vf, maybe around 350mVf to 380mVf.
Again a 3pr output stage will need to pass just 2.4A (for 380mVf) to bring the diodes into play.
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Your example is biased to 2.6A and it stays in ClassA all the way up to 5.1Apk.
You are confirming that the example will start drawing Diode current @ ~3.2A passing the output device (not equal to output current).
I.E. the diodes are passing long before the amp leaves ClassA
This confirmation is the complete opposite to what you answered earlier:
100W at 8ohm=28.28V
28.28V/8ohm=3.5A not 5.2A
i never said the do not conduct while the amp is still in class A. 5.2A (wich will be peak class A) is way over 100W. its 216W
and in most cases, the diodes start conducting at a higher lewel then 400mV drop. if not, take the bias Down a notch or get lower source resistance.
28.28V/8ohm=3.5A not 5.2A
i never said the do not conduct while the amp is still in class A. 5.2A (wich will be peak class A) is way over 100W. its 216W
and in most cases, the diodes start conducting at a higher lewel then 400mV drop. if not, take the bias Down a notch or get lower source resistance.
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Perhaps I should have been more specific:
I am building a V3 Turbo with 4prs output devices. 34V transformer secondaries with estimated 45V loaded rails. I think I have enough heatsink to be able to bias at 0.31V across the paralleled 1ohm resistors to give bias current of 0.62A per device to give about 100W rms Class A into 8 ohms.
Looking at the Vishay MUR3020W chart for If vs. Vf it appears that at a Tj of 50C (Mosfet and diode side by side on heatsink at 50C) the diode starts conducting at about 0.42V which across 0.5ohm resistance equates to 0.84A. Does this not mean that in this example the diodes will not conduct until the amp leaves Class A?
The set up you describe will allow the diodes to conduct while still in ClassA.
