No, not yet. Do I need to desolder them, and bias without them connect to the PCB?
I don’t see any signs of damage / burned Mosfets (or is this not visible from the outside?).
The channel was not properly biased.
I played music for an hour with these settings until R4 started smoking:
• 0.5v DC Offset
• 0.327v across R2
Will this automatically cause burned mosfets? (I don’t feel like desoldering them without suspecting them to be burned. But that’s just my inexperienced opinion).
I played music for an hour with these settings until R4 started smoking:
• 0.5v DC Offset
• 0.327v across R2
Will this automatically cause burned mosfets? (I don’t feel like desoldering them without suspecting them to be burned. But that’s just my inexperienced opinion).
Hello Dennis,
• Z1/Z2 = 5.1v
• R7/R8 = 10K
• Voltage across R2 was (with DC offset close to zero) max 0.327v (this wasn’t going higher).
In which direction should I turn P1 and P2 before I power up, fully clockwise or fully counterclockwise?
Koos
If you remove the mosfets you can monitor the voltage across R2 at either extreme of the pot as mentioned by ZM with no fear of killing transistors.
You may also want to make a mains lightbulb tester (plenty of recipes here on diyaudio) for next time you start up. Mind you, you won't be able to bias with it in place, but it may save precious components in case of a fault on startup.
You may also want to make a mains lightbulb tester (plenty of recipes here on diyaudio) for next time you start up. Mind you, you won't be able to bias with it in place, but it may save precious components in case of a fault on startup.
You might need to increase the zeners higher (to say 6.2V). Consider also
decreasing R7/R8 to give a bit more current to the zeners.
The direction may depend on your pot and the orientation it was soldered in.
(Though with a low-ish value zener like a 6.2V, midpoint on the pot should
be safe) Removing the mosfet allows you to test out the direction and range
of voltage without fear of massive current from the mosfets.
Do consider also building a bulb tester.
decreasing R7/R8 to give a bit more current to the zeners.
The direction may depend on your pot and the orientation it was soldered in.
(Though with a low-ish value zener like a 6.2V, midpoint on the pot should
be safe) Removing the mosfet allows you to test out the direction and range
of voltage without fear of massive current from the mosfets.
Do consider also building a bulb tester.
Thanks for the clear explanation.
I might have all the parts to make a mains lightbulb tester. I will gather all the parts for this.
Koos
Thank you Dennis for explaining, this is all clear for me now.
I will order new resistors (I need to have new ones for R4 anyway) and I will order different values for R7/R8.
For Z1/Z2 I already have the option to replace the 5.1v by 6.2v (they were in the F6 kit from the diyaudio store).
Once the new parts arrive I will desolder the mosfets to safely test the direction and voltage range.
In the meantime while I am waiting on the parts I can prepare a lightbulb tester.
I will post updates once I have some test results.
Koos
Thank you Dennis for explaining, this is all clear for me now.
I will order new resistors (I need to have new ones for R4 anyway) and I will order different values for R7/R8.
For Z1/Z2 I already have the option to replace the 5.1v by 6.2v (they were in the F6 kit from the diyaudio store).
Once the new parts arrive I will desolder the mosfets to safely test the direction and voltage range.
In the meantime while I am waiting on the parts I can prepare a lightbulb tester.
I will post updates once I have some test results.
Koos
Lightbulb tester helped me out as well, just a bulb fitting with some "kroonsteentjes" in series with fase.
Mine is blowing fuses 1,25A on startup with CL60 (10r) in series with "hot". so the bulb tester is currently back in and will replace the thermistor with a higher value, probably 60r.
What value did you use on the thermistor?
Thanks for the advise, I will use a light bulb tester for sure, many recommendations so I will not take the risk to do it without now
The new resistors arrived today, including different values, so coming weekend it is time to play again.
Looking forward, I miss that clean sound that was coming out of the F6
Koos
Me too! Expect the fuses to come in tomorrow. Then up next is to try to solve a mechanical buzz in my toroidy 400va transformer, which I unfortunately also hear when holding my ear close to the speaker. I have coax signal cables and tried to move power lines far from speaker lines. Any suggestions? Trafo is mounted on L bracket simalar to 6L6 his build. I think the buzz is more prominent on the transformer during power net rush hours..
Have you installed SLOW BLOW fuses?
What VA rating?
What mains AC do you have 110/120/220/230/240V
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Thanks! so I understand that original pass f6 uses 300va transformer.. I Did not think or know of recalculating 400/230 for the fuse..
All good.
You shouldn't have any further problems once you install the new fuses.