Super nice.
Thank you, Sir!
More progress and all good news. Did all the voltage checks and biased up the front end. No drama.
Couple clarifying questions:
- The 1.2V drop for R5/R6 is an intermediate value and the final target is 1.5V after leisurely warmup, correct?
- T18 (offset) was super duper twitchy and could vary ~500mV with some pressure on the trimpot or blowing on the devices. I could get it to ~60mV, but I don't have much confidence it'll stay there. Normal for this point?
- The 2nd draft 8/8/16 pdf refers to R6 (T9 and T10) voltage drop. This should be T8 and T9, correct?
Next I'll install the VFETS - wish me luck!
Below you can see my chassis arrangement and signs of life.
BK
Attachments
See your quote above for what I found biasing mine.
You are very close. You will not be able to bias the V-fets to where they should be without 1.5V across R5 and R6. I almost forgot to mention, great looking build. Clean the pins of the V-fets to remove any grease before soldering. It is going to be hard fooling with grease not to get it on everything you touch. I used a q tip and alcohol and then soldered.
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Beauty build & excellent wiring quality.
Any main power wire with bulb " tester" at hand for first start up ?
Congratulations and big magic smoke !
Beauty build & excellent wiring quality.
Any main power wire with bulb " tester" at hand for first start up ?
Congratulations and big magic smoke !
I do believe I see a variac in the picture.
Just interested by your amp inside
now i see variac and Variac as well
Have fun !
Greetings
Thanks, guys. Been monitoring for the last few hours and everything is rock solid, so I think all is well so far.
Yep, that's the 4U chassis + TeaBag 40mm PSU board and a 400VA SumR transformer wound extra beefy for Class A. I should have gone with black front panel to complete the murdered theme!
I use the variac with a low amp fuse and dial it up quickly to a position I've marked for my particular mains output. Bulb circuit for initial startup is probably a really good idea, but my impression is that following NP's instructions pretty well de-risks gotchas at this point.
BK
Yep, that's the 4U chassis + TeaBag 40mm PSU board and a 400VA SumR transformer wound extra beefy for Class A. I should have gone with black front panel to complete the murdered theme!
I use the variac with a low amp fuse and dial it up quickly to a position I've marked for my particular mains output. Bulb circuit for initial startup is probably a really good idea, but my impression is that following NP's instructions pretty well de-risks gotchas at this point.
BK
Nah, it actually has a lot of silver inside too, and I prefer a silver front panel!
Variac ll
Variac ll
After reading the instructions more carefully this morning I believe you are correct, typo. Later in the instructions Mr Pass definitely defines R6 test points as T8 and T9.
I did not short mine. The offset is just very sensitive. A little movement moves the offset a lot. Mine would go from mv to many volts with just a little movement of the pots. Your observation is exactly what I found. Proceed.
Thanks wdecho. Question still remains - is it preferable here to short the input during the bias procedures? I want to think yes, but would be great to get the official word.
BK
