FPIII Resistance Check Results

[Paul Joppa]

No, I'm saying you don't know if you don't check. I looked at two data sheets and found no specification for the can connection; I tested three electrolytic caps that were at hand and found the can to be insulated from the leads. I have some non-electrolytic caps within easy reach rated 36uF/3800vDC, on which the negative terminal is welded directly to the can.

But we do not check for this, and it is not always specified by manufacturers, so there's no guarantee that the can is isolated or will remain isolated if we change the source of the part or that the manufacturer won't change the part in production - it would still meet the specs, after all.

 

[Paul Joppa]

Oh yes - the switch noise could also be a poor solder connection, either on the pot itself or on one of the wires connected to it.

Bottlehead will replace the switch if it is defective, but it's a lot less hassle to re-flow the solder connections!

 

[Frank Breech]

Ok.  WIll reflow all solder connection to that pot and get back to you. 
Thanks

 

[Laudanum]

Mike ... regarding your 12AU7 tubes, I am assuming that you have the EH tubes as shipped with your kit.  I could be wrong but I believe that they have spiral filaments and generally dont glow.  Or, atleast not as brightly as most tubes.  If you look down from the top, you probably will be able to see some glow if you dont see any from the side.  But the FPIII wouldnt work if those tubes werent.  Funny but most of the 12AU7's I have tried in my headphone amp (Crack) have been pretty bright including the one that's in there now (it's an old stock tube).  I built the FPIII with 6SN7 tubes and the Sylvania tubes in there dont glow much compared to the other tubes on the rack.  Different tube, same "problem".  I like the glow but the sound is more important 

 

[Frank Breech]

Laudanum, this could make sense ... when I did the smoke test and let everything go for 30 sec as indicated in the instructions, I was looking down on the tubes.  Now, in my rack, there's no space for me to get my head over them when on, so I'm only looking at them from the side.  I'll look into this and see if I see glowing ....

However, I have a bigger problem.  I was 'messing around' thinking about the dirty pot sound that I'm getting out of my right SW pot.  My rack shelves are glass, so I can actually look under the FPIII.  I noticed that the noisiness seemed to be related to how the right 12AU7 was seated in the socket. The LED on the underside would flicker on and off with the slightest touch of the tube and each touch also incited the same noise and some nasty popping i would hear when adjust that right channel SW.  I turned my amp off and investigated a little further, wiggling the tube in the socket to get it seated in there alright.
Then - and I can't remember exactly what happened, but at some point I turned off the FPIII and turned it back on - and after that nothing.  The LEDs at the underside 12AU7 sockets are not lit.  The OD3 still lights up just fine.  But, no music. 
Shoot ... what the heck?