@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?
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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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?
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?