Obviously not everyone will use a brass plate to build his own "clone" That manages room for departure from the original schema, as per :
EDIT: please note - as mentionned by Charlie Wilson below - that the grounds from the board are not soldered to the brass plate but directly to the chassis, instead.
Anyway, what questions me right now is:
- if the brass plate is some sort of best grounding point, why aren't the cathode resistors of V1 connected to the brass plate?
Last edited by ChopSauce on Fri Nov 19, 2021 2:07 pm, edited 1 time in total.
I will try to answer what worked great on the builds I did, but it will not help answer your specific questions I am afraid.
I had best results in keeping B+1 and B+2 grounded at the PT with the OT/speaker and output tube grounds (1star ground for all these, including the heaters balance resistors ground).
And all other node ground close to the input jack.
Input cable is shielded (with better results with RG59)
ChopSauce wrote: ↑Thu Nov 18, 2021 8:07 am
if the brass plate is some sort of best grounding point, why aren't the cathode resistors of V1 connected to the brass plate?
My guess is the brass plate might not be the best ground since it may develop corrosion at its interface with the chassis.
Funny. This morning I thought I could have put a brass plate with conducting grease...
fred.violleau wrote: ↑Thu Nov 18, 2021 3:44 pm
I had best results in keeping B+1 and B+2 grounded at the PT with the OT/speaker and output tube grounds (1star ground for all these, including the heaters balance resistors ground).
And all other node ground close to the input jack.
Input cable is shielded (with better results with RG59)
Fred.
Thx Fred, for sharing these details. I can hardly believe that you had the best results with B+3 (PI) grounded with the inputs, but the VVR from my build adds a few degrees of freedom to the grounding optimisation problem...
I think Dumble did it that way for a more practical reason. With the 5C3 brass plate being kind of narrow, there is not much room to put a solder blob where the input jacks are on the brass plate. Please note that ALL of the grounds are below the brass plate to the chassis. Dumble's and Fender's grounding schemes have always worked well for me if they are followed just the way they did it.
CW
Of course. I understand that having managed to "replace" the brass plate with a ground bus sent me out of the secured path.
I'm not sure about what you meant by "under the brass plate", though. On the layout the connection seems to be on the brass plate. Do you mean it is actually soldered directly to the chassis, rather than to the plate?
ChopSauce wrote: ↑Thu Nov 18, 2021 8:07 am
if the brass plate is some sort of best grounding point, why aren't the cathode resistors of V1 connected to the brass plate?
My guess is the brass plate might not be the best ground since it may develop corrosion at its interface with the chassis.
Martin is again dead on!
I have an Older 5C5 1949 Pro that when I got it had an awful hum (This was back before I started doing amps), So I took it to Jeff Bober, the problem was the brass plate got so corroded it lifted ground. His remedy solder cathodes & input jack to the chassis
Tony
" The psychics on my bench is the same as Dumble'"
fred.violleau wrote: ↑Thu Nov 18, 2021 3:44 pm
I had best results in keeping B+1 and B+2 grounded at the PT with the OT/speaker and output tube grounds (1star ground for all these, including the heaters balance resistors ground).
And all other node ground close to the input jack.
(This was back before I started doing amps), So I took it to Jeff Bober, the problem was the brass plate got so corroded it lifted ground. His remedy solder cathodes & input jack to the chassis