I did remove the bulb, but stille running with a 1A fuse.
I already have 0.6v across the source resistors, but only 2.6V bias, probably because I use the Toshibas, think they have a lower turn on voltage.
I did post pictures a few pages back 🙂
But I will report back with my results - I feel that people often forget that.
I already have 0.6v across the source resistors, but only 2.6V bias, probably because I use the Toshibas, think they have a lower turn on voltage.
I did post pictures a few pages back 🙂
But I will report back with my results - I feel that people often forget that.
current* is what's important ( voltage across source resistor) and output offset at 0
you don't need to care for Ugs , except in case of troubleshooting
*Iq , more precisely
you don't need to care for Ugs , except in case of troubleshooting
*Iq , more precisely
Arthur - do you have 0.6V across the source resistors with zero offset? If so, the bias is set - put the lid back on and listen to it for an hour, then re-adjust as necessary.
I have 0.6V across the source resistors, but there are no balance pots on the Cviller v2 boards, and I must admit that I didnt check if there is DC on the outputs.
I will do that when I have assembled the other side and powered it up again.
Thanks for your replies.
ZEN: IQ could be mistaken 🙂)
I will do that when I have assembled the other side and powered it up again.
Thanks for your replies.
ZEN: IQ could be mistaken 🙂)
two drain pots are having balancing action , against each other
regarding IQ , I'm not counting on mine , usually
do not forget - intended Iq - at temperature equilibrium state
regarding IQ , I'm not counting on mine , usually
do not forget - intended Iq - at temperature equilibrium state
If you haven't checked for DC on output, you are not done.
Do that and adjust it out (below 10mV). You will use one pot, turn up or turn down, recheck .6V across source resistors, close on this voltage is OK f zero on output.
Rush
adjusting bias
I am just jumping in here. With much help from these forums, I built an F5. First class A MOSFET amp for me. Here is what I did FWIW.
As 6L6 said, put the top on (no need to screw down) and let the amp get to operating temperature. Keep one of the DVM monitoring a resistors and check voltages every 15 minutes. Another DVM monitoring speaker output. I started with bias at .5v and adjusted close to .6v, with just a few millivolts on the speaker leads. Another great tool was a cheap digital infrared thermometer. Mine was US $15 on a 'Deal of the Day' site. I checked the heatsink temperature when I checked the bias, every 15 minutes. Goal was to stay below room temperature +25C. Stablized at RT +22C, so heat was not a problem with the 4U case. You can also monitor FET output temperature, good for troubleshooting.
I hooked up an old iPod and looped on the music for about 4 hours. As the amp heated up, the bias did change slightly. At hour 4, the bias had not changed significantly in the previous hour. Time to tweak to .6v bias/ 0v output exactly, button it up and enjoy!
I am just jumping in here. With much help from these forums, I built an F5. First class A MOSFET amp for me. Here is what I did FWIW.
As 6L6 said, put the top on (no need to screw down) and let the amp get to operating temperature. Keep one of the DVM monitoring a resistors and check voltages every 15 minutes. Another DVM monitoring speaker output. I started with bias at .5v and adjusted close to .6v, with just a few millivolts on the speaker leads. Another great tool was a cheap digital infrared thermometer. Mine was US $15 on a 'Deal of the Day' site. I checked the heatsink temperature when I checked the bias, every 15 minutes. Goal was to stay below room temperature +25C. Stablized at RT +22C, so heat was not a problem with the 4U case. You can also monitor FET output temperature, good for troubleshooting.
I hooked up an old iPod and looped on the music for about 4 hours. As the amp heated up, the bias did change slightly. At hour 4, the bias had not changed significantly in the previous hour. Time to tweak to .6v bias/ 0v output exactly, button it up and enjoy!
Hi Rush,
I know - one channel still looks like spaghetti with leads pointing in all direction 🙂
I disassembled it in the process of fault finding.
So far it seems that my own failure where to turn the bias in the wrong direction at startup, and then I had the short in the PSU coil. Everything else seem to work like inteded - yet!
I know - one channel still looks like spaghetti with leads pointing in all direction 🙂
I disassembled it in the process of fault finding.
So far it seems that my own failure where to turn the bias in the wrong direction at startup, and then I had the short in the PSU coil. Everything else seem to work like inteded - yet!
Hi crcook,
thank you for your input, I have already thought about buying one of those modern IR thermometers, and I will do that tomorrow.
One of my favorit shops (Swedish Biltema) is 1 km from where I live.
Prices are higher here, but still reasonable. My heat sinks are 12 x 5 x 1,5".
thank you for your input, I have already thought about buying one of those modern IR thermometers, and I will do that tomorrow.
One of my favorit shops (Swedish Biltema) is 1 km from where I live.
Prices are higher here, but still reasonable. My heat sinks are 12 x 5 x 1,5".
With around 0.66V across the resistors I am able to get around 0.5mV on the outputs.
For a short time at least.
For a short time at least.
But the heat sinks feel not more than 10 degrees above ambient.
And I thought they were a little bit on the low side in terms of size.
And I thought they were a little bit on the low side in terms of size.
you're able to achieve that with less voltage across Rs ; there is no correlation between these two - Urs and output offset
Yes, I suppose you could get balance by all voltages, but I have 0.66V across Rs, and therefore I just wonder why my heat sinks not get hotter.
I suppose they should be around 55 degrees with that bias and that size.
I suppose they should be around 55 degrees with that bias and that size.
be sure that mosfets aren't much hotter then heatsinks
that would be sign of bad thermal connection between mosfet cases and heatsink
what you're using for thermal insulation/management ?
that would be sign of bad thermal connection between mosfet cases and heatsink
what you're using for thermal insulation/management ?
As you can see on the pictures my heat sinks are completely separatet from the box.
Wonder if that makes a big difference.
Maybe they are at 40 degrees now, but that is still not much, compared to what I thought it would be.
Wonder if that makes a big difference.
Maybe they are at 40 degrees now, but that is still not much, compared to what I thought it would be.
I use Mica washers with a thin layer of thermal compound.
And when I put my fingers directly on the mosfets it is about the same.
And when I put my fingers directly on the mosfets it is about the same.