Grounding on the Crack

[reglys]

Hi
1) What is the purpose of grounding the terminal 16 on the 6-lug terminal strip. Is it for frame transformer grounding?
2) Does the acronym PSU on the CRACK schematic (p.6 of the user manual) means Power Supply Unit? According to this schematic, the PSU ground should be connected to the incoming ground. Where is this physical connection? Does this connection is already made by default?
3) I was just wondering about the arrow (B+) on the Power supply schematic. Instead of going to the right it should go to the left. Isn’t it? Same thing for arrows about the tube heaters. Not sure about the direction of arrow PSU Ground. Furthermore, the arrow (to left channel) in the Right Channel schematic should go to the right instead of the left. Isn’t it?
The arrows (from left channel, B+ and PSU ground) are OK for me.

Thank you in advance

 

[Paul Birkeland]

Terminal 16 gets earthed to earth the transformer cover and the transformer stack. Yes, PSU is power supply unit. The audio ground and the chassis earth connect at terminal 3. The ports on the schematic are placed in the most convenient place.  For example, the PSU ground would more accurately be drawn as coming into the headphone jack, but for the purposes of the kit schematic it's more convenient to simply draw it as shown.  Similarly the schematic shows separate ground wires for each channel going to the potentiometer, which is not reflected in the build.  The Crack schematic is a little unique as it was drawn out formally long after the first amp or two were built, but it's certainly sufficiently representative to understand what's going on.

 

[reglys]

Thank you Paul for your fast reply.

Now I can see the connection between the audio ground and the chassis earth. 

Terminal 3 is already bonded to the chassis. Make a lot of sense now. I was too focus on the 6-lug terminal strips expecting a ground connection between audio ground and chassis earth at this spot.

Thank you again