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Mojo Champ Kit Problems
Good News...........
It works. V1a & b plate voltages have dropped to 203 & 200 respectively and pins 3 & 8 are at 1.62 & 1.51 respectively. I can't say that I'm overly impressed with the sound but it's a start & it certainly sweetens with old RCA valves installed at V1 & V2 rather than the supplied JJ's. (I've not swapped the 5Y3 yet but I imagine a few less volts may further tame brashness).
Bad News..........
I'm not happy with the level of hum & hiss. I know these 'Tweed Era' Champs have a bit of a reputation in this regard but I think it's excessive.
What I've Done So Far...........
1. Installed the correct 100K plate resistors.
2. Moved the 2x100R 6.3v virtual centre tap to the pilot lamp.
3. Completely replaced the heater wiring per the Tube Amp Doctor photos i.e. elevated above the board, tightly twisted, direct to the pins & no looping around sockets.
4. Shortened many leads & re-routed to avoid wires crossing where poss.
5. Scrapped the Mojo/old Fender grounding system (dreadful), tried the Tube Depot method (a little better) & currently have the TAD system in place which is better than the other two but not fab!
6. Put ali shielding on the cab back pane & ensured contact with chassis.
What I've Not Done Yet......
1. Reduced the length of the PT 5v filament supply leads.
2. Reduced the length of the PT B+ leads.
3. Moved the B+ centre tap; it is currently grounded with the mains earth.
Any top tips to help me reduce the hum further would be appreciated.
Cheers
Good News...........
It works. V1a & b plate voltages have dropped to 203 & 200 respectively and pins 3 & 8 are at 1.62 & 1.51 respectively. I can't say that I'm overly impressed with the sound but it's a start & it certainly sweetens with old RCA valves installed at V1 & V2 rather than the supplied JJ's. (I've not swapped the 5Y3 yet but I imagine a few less volts may further tame brashness).
Bad News..........
I'm not happy with the level of hum & hiss. I know these 'Tweed Era' Champs have a bit of a reputation in this regard but I think it's excessive.
What I've Done So Far...........
1. Installed the correct 100K plate resistors.
2. Moved the 2x100R 6.3v virtual centre tap to the pilot lamp.
3. Completely replaced the heater wiring per the Tube Amp Doctor photos i.e. elevated above the board, tightly twisted, direct to the pins & no looping around sockets.
4. Shortened many leads & re-routed to avoid wires crossing where poss.
5. Scrapped the Mojo/old Fender grounding system (dreadful), tried the Tube Depot method (a little better) & currently have the TAD system in place which is better than the other two but not fab!
6. Put ali shielding on the cab back pane & ensured contact with chassis.
What I've Not Done Yet......
1. Reduced the length of the PT 5v filament supply leads.
2. Reduced the length of the PT B+ leads.
3. Moved the B+ centre tap; it is currently grounded with the mains earth.
Any top tips to help me reduce the hum further would be appreciated.
Cheers
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