Two POINT four five VOLTS (2.45V)
or
0.245V (Two hundred forty five Millivolts?)
Proper bias is 0.5 to 0.6V (500mV) across R2 (0.47ohm)
Going to order F6 parts soon. Looking at the CPF3 resistors as recommended, and I am confused... Of the several models of 3W, the ones with worse specs cost more than the ones with better spec (like CPF3100R00BEE36 vs CPF3100R00DKE14). Am I missing something, and which should I be getting?
Thanks!
I was told just cpf3 as a recommendation, I didn't see any specific sku (tho I may have missed it...)
I have a working F6 that I use with phone and Doug self pre or nodi 2i. I just completed a SP14 6sn7 tube pre when I hooked to the f6 I got a load buzz and smoke turned every thing off f6 still works. Took cover off f6 hooked the sp14 up I did not turn the preamp on only the f6 just to see what might happen. Seconds after the f6 was turned on the red led on the Diy power supply started to dim and smoke came off the 4 3 watt resistors on the right channel. I had a similar result when I tried the f6 with a NAD streamer/dac. The sp14 pre works fine with my tube lab amps. any ideas I am thinking some kind of grounding issue due to the fact the sp14 did not need to be turned on?
You have two threads with this question.
For others that have ideas, want to see a more complete run-down of the situation, and don't want to repeat other's recommendations, below is the thread.
F6 smokes with preamp
From what I've seen on the other thread re: two situations with smoke, below are my quick thoughts. You didn't mention in this thread that the F6 was under power when you connected/disconnected inputs in at least one situation and possibly two. That is valuable information to those that will try to help. You'll probably have to do some checks and likely some repairs along with changing some behavior.
My WAG is that you did some damage to the F6 when you released the magic smoke hooking up the SP14 the first time, then did more damage in another area when you did not fix what initially smoked before testing again.
1) Please stop connecting and disconnecting inputs while any amp is powered up. (Smoke #1)
Find out what caused the smoke, and repair before trying the same thing again. Hopefully you will never see smoke again, but just turn off the amp if you see smoke or other fault indications. Don't move the inputs around or disconnect while under power (smoke #2)
2) Remove amp boards from PSU and test your PSU. You've been given suggestions re: what to check re: soldering, resistors, etc. Any time resistors are discolored, it would be wise to check them. Personally, I would just replace them. You have to remove at least one leg to check them, and checking low resistances with only a standard handheld DMM can yield inconsistent/inaccurate results. If you happen to have a DMM capable of measuring consistently below 1 ohm, or know how to check low resistances with other techniques, then you can do that. You never answered how your amp was fused. Proper fusing may have prevented some damage. No way to know, and it's not the root cause, but it was a valid question. If you don't have a properly rated fuse, I'd put one in.
3) Remove and troubleshoot each amp board independently. Smoke from the transistors (you did not mention whether it was MOSFETs or JFETs) is never a good sign. Even if the amp is still "working", it is possible that it's not working well.
4) I'd recommend using a DBT and/or Variac as part of final checks for #2 and #3.
5) It's possible that a grounding issue could have been part of the root cause, but you'll still have to check your PSU/amp boards. While doing that, any grounding/shorting issues will become apparent, and you can fix it.
No way to really know the root cause in each case without more information, but the only new addition to the mix is the SP14 and how you initially connected it to the F6. You can check the output voltage of the SP14 at turn on/off and during steady-state also for peace of mind.
tl;dr - some investigation into SP14 is recommended. Repairs to the F6 are likely needed. Post the steps you've taken along with pictures and measurements if you run into anything you don't feel comfortable with.
Good luck!
For others that have ideas, want to see a more complete run-down of the situation, and don't want to repeat other's recommendations, below is the thread.
F6 smokes with preamp
From what I've seen on the other thread re: two situations with smoke, below are my quick thoughts. You didn't mention in this thread that the F6 was under power when you connected/disconnected inputs in at least one situation and possibly two. That is valuable information to those that will try to help. You'll probably have to do some checks and likely some repairs along with changing some behavior.
My WAG is that you did some damage to the F6 when you released the magic smoke hooking up the SP14 the first time, then did more damage in another area when you did not fix what initially smoked before testing again.
1) Please stop connecting and disconnecting inputs while any amp is powered up. (Smoke #1)
Find out what caused the smoke, and repair before trying the same thing again. Hopefully you will never see smoke again, but just turn off the amp if you see smoke or other fault indications. Don't move the inputs around or disconnect while under power (smoke #2)2) Remove amp boards from PSU and test your PSU. You've been given suggestions re: what to check re: soldering, resistors, etc. Any time resistors are discolored, it would be wise to check them. Personally, I would just replace them. You have to remove at least one leg to check them, and checking low resistances with only a standard handheld DMM can yield inconsistent/inaccurate results. If you happen to have a DMM capable of measuring consistently below 1 ohm, or know how to check low resistances with other techniques, then you can do that. You never answered how your amp was fused. Proper fusing may have prevented some damage. No way to know, and it's not the root cause, but it was a valid question. If you don't have a properly rated fuse, I'd put one in.
3) Remove and troubleshoot each amp board independently. Smoke from the transistors (you did not mention whether it was MOSFETs or JFETs) is never a good sign. Even if the amp is still "working", it is possible that it's not working well.
4) I'd recommend using a DBT and/or Variac as part of final checks for #2 and #3.
5) It's possible that a grounding issue could have been part of the root cause, but you'll still have to check your PSU/amp boards. While doing that, any grounding/shorting issues will become apparent, and you can fix it.
No way to really know the root cause in each case without more information, but the only new addition to the mix is the SP14 and how you initially connected it to the F6. You can check the output voltage of the SP14 at turn on/off and during steady-state also for peace of mind.
tl;dr - some investigation into SP14 is recommended. Repairs to the F6 are likely needed. Post the steps you've taken along with pictures and measurements if you run into anything you don't feel comfortable with.
Good luck!
Last edited: