@Dennis Hui that's a relief. Thanks @Mikerodrig27. Are K thermocouples good enough for our purpose or is it better to use an infrared gun?
Initial start up continuing, I connected the first side of my F6 and the blue LED lit up on the amp board but I am getting zero voltage across the .47 on resistor. The voltages in the power supply all check out. There seems to be no heat being generated by any of the devices on the amplifier PCB. I have turned the screw on the bias potentiometer quite a bit in each direction and see no response on the voltmeter. Any idea what might be going on?
Do you know if they should be turned clockwise or counter clockwise? Also I could’ve added that I did check the offset and there was a slight voltage there that I was able to zero out.
Update: I started turning counter clockwise and I am getting a voltage rise. Things are back on track 🙂
What voltage Zener are you running and what resistor in in the R7 and R8 spots? If you are running the trimmer pot to it's limit, consider the tweaks mentioned in this thread. Glad it is showing life!
This F6 is built to the stock specifications. Zeners one and two are 5.1 V. R 7 and 8 are each 10 K resistors. So far I can bias up to .34 V before the potentiometer tops out and I can get the offset down to .17 volts before that potentiometer bottoms out. 6L6’s instructions suggest going up in half volt steps with the seniors but given where I am currently out can you suggest the voltage that would get me into the ballpark on one try?
Another option is the picodumb mod where you use a string of three LEDs in series in place of the zener. If you turn the amp on and off often, this mod helps your amp get up to temperature quicker. He would still need the 3.3 k resistors.
There should be someone who referenced it in this thread otherwise you can search for the picodumb mod thread.
There should be someone who referenced it in this thread otherwise you can search for the picodumb mod thread.
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The "three green led" mod works great as well. 🙂
3k3 resistors as above.
(I am listening to that now.)
3k3 resistors as above.
(I am listening to that now.)
I happen to have four 3.3 thousand ohm resistors but they are quarter watt. Do I need the three watt type?
also, no specs on the LED, any old green one will do 🙂?
also, no specs on the LED, any old green one will do 🙂?
Recommended green led is this https://eu.mouser.com/ProductDetail/Lite-On/LTL-4231?qs=ijkchSGtXvugYEuZKOTKWw==
3k3 are 1/4w
Background article https://www.diyaudio.com/community/...ps-possibly-my-dumbest-idea-yet.348969/page-2
3k3 are 1/4w
Background article https://www.diyaudio.com/community/...ps-possibly-my-dumbest-idea-yet.348969/page-2
Thank you for the link to this thread. It was good reading and I am definitely going to try the three LED solution. I wonder if anyone has dreamed up interesting aesthetic approaches regarding the three green LEDs. The inside of this amp is going to be pretty colorful.
While waiting on the parts to get my F6 properly biased up I hooked it up to some speakers anyway, And it may be of interest to some that it sounds very good! I’m curious when the bias does get raised will the sound change or will I primarily get increased amplification?
If by "increased amplification" you mean voltage gain, then that won't happen. Objectively you will have greater class A envelope, lower distortion and more heat.
Just curious if you ever measured the voltages across the zeners and if they were close to 5.1V.
Just curious if you ever measured the voltages across the zeners and if they were close to 5.1V.
My "faulty" channel still giving me problems...
Installed new MOSFETs and unfortunately those got blown. 🙁 Also blown was the 0.47 ohm R2 source resistor. The R1 (also 0.47 ohm) did not blow.
Now testing without MOSFETs installed.
Measuring across the LEDs (have Pico mod LED installed instead of Zener), and getting 5.85V
The P2 bias trimpot is working - managed to adjust the voltage on the Q2 MOSFET Source and Gate points to 3.80 V; across the Source to Drain points it measures 23.6V, and across Drain to Gate points measures 19.8V.
The P1 trimpot pot is also working - could adjust the voltage for Q1 GDS points too. for Q1 MOSFET, measuring between Source and Gate points gives 3.80 V; then across Source to Drain points it measures 23.6V, and across Drain to Gate points getting 19.8V.
Do these look ok? Anything else I should measure before considering putting in a set of new MOSFETs?
Installed new MOSFETs and unfortunately those got blown. 🙁 Also blown was the 0.47 ohm R2 source resistor. The R1 (also 0.47 ohm) did not blow.
Now testing without MOSFETs installed.
Measuring across the LEDs (have Pico mod LED installed instead of Zener), and getting 5.85V
The P2 bias trimpot is working - managed to adjust the voltage on the Q2 MOSFET Source and Gate points to 3.80 V; across the Source to Drain points it measures 23.6V, and across Drain to Gate points measures 19.8V.
The P1 trimpot pot is also working - could adjust the voltage for Q1 GDS points too. for Q1 MOSFET, measuring between Source and Gate points gives 3.80 V; then across Source to Drain points it measures 23.6V, and across Drain to Gate points getting 19.8V.
Do these look ok? Anything else I should measure before considering putting in a set of new MOSFETs?