Ceriatone Chupacabra mods

[FourT6and2]

I have 145 on v1a

I have changed the PT and I have a B+ of 460 v

How do I raise the v1a?

Been 2+ years haha!

145v on V1a is too low. 460v B+ is ok. What have you done to the amp since you last posted in this thread? Hard to give you suggestions without knowing what else you changed.

But, if everything else is still stock Chupacabra spec, then I recommend:

1. Adding the missing 10K dropping resistor between PI and V2 cathode follower.
2. Lower V1a plate resistor to at least 330K.
3. Change V1a cathode to 2K7 / 0.68uF.
4. Change V1b cathode to 2K7 / 0.68uF.

5. Slope resistor to taste 47K, 39K, 33K, etc.
6. NFB to 47K 8 ohm tap.
7. Depth to 2200pF or 3300pF or leave it at 4700pF if you like it.
8. V1b input grid resistor to 68K.
9. Feel resistor can stay at 82K, but if you downtune a lot or run a boost, change to 68K.

 

[peterc52]

Been 2+ years haha!

145v on V1a is too low. 460v B+ is ok. What have you done to the amp since you last posted in this thread? Hard to give you suggestions without knowing what else you changed.

But, if everything else is still stock Chupacabra spec, then I recommend:

1. Adding the missing 10K dropping resistor between PI and V2 cathode follower.
2. Lower V1a plate resistor to at least 330K.
3. Change V1a cathode to 2K7 / 0.68uF.
4. Change V1b cathode to 2K7 / 0.68uF.

5. Slope resistor to taste 47K, 39K, 33K, etc.
6. NFB to 47K 8 ohm tap.
7. Depth to 2200pF or 3300pF or leave it at 4700pF if you like it.
8. V1b input grid resistor to 68K.
9. Feel resistor can stay at 82K, but if you downtune a lot or run a boost, change to 68K.

I know. Haha finally have the room to try some building and playing.

I bought the Yeti transformer 350-350 and installed it last week. Raised the dropping resistor before the PI node from 10k to 20k - perhaps too much?

From the start of the this thread I have changed:

1. Adding the missing 10K dropping resistor between PI and V2 cathode follower.
2. Lower V1a plate resistor to at least 330K.
3. Change V1a cathode to 2K7 / 0.68uF.
4. Change V1b cathode to 2K7 / 0.68uF.

5. Slope resistor to taste 39k
6. NFB to 47K 8 ohm tap.

 

[FourT6and2]

I know. Haha finally have the room to try some building and playing.

I bought the Yeti transformer 350-350 and installed it last week. Raised the dropping resistor before the PI node from 10k to 20k - perhaps too much?

From the start of the this thread I have changed:

1. Adding the missing 10K dropping resistor between PI and V2 cathode follower.
2. Lower V1a plate resistor to at least 330K.
3. Change V1a cathode to 2K7 / 0.68uF.
4. Change V1b cathode to 2K7 / 0.68uF.

5. Slope resistor to taste 39k
6. NFB to 47K 8 ohm tap.

Raising that first dropping resistor LOWERS the preamp voltages. Put it back to 10K for sure. Amp will tighten up, get less fizzy/hairy, and sound stronger overall. Plenty of gain on tap already + diodes = you don't need "brown sound" by lowering voltages.

You can also get rid of all the stuff on V1a input grid. All you need is a 1M on the input jack for ground reference and a small grid stopper on the socket, like 27K - 33K. But only do this once you get V1a plate voltage up above 160v.

Another thing to do would be to replace the lower voltage diodes with either MPSA06 or 2N5401. So you have 18v zeners on one side of the switch and a more angry, less compressed sound on the other for modern sounds instead of the super low voltage diodes Ceriatone uses.

Anyway... yeah, go back to 10K dropper and your preamp voltages will come up where they need to be.

The other stuff you already did should be great.

 

[peterc52]

Raising that first dropping resistor LOWERS the preamp voltages. Put it back to 10K for sure. Amp will tighten up, get less fizzy/hairy, and sound stronger overall. Plenty of gain on tap already + diodes = you don't need "brown sound" by lowering voltages.

You can also get rid of all the stuff on V1a input grid. All you need is a 1M on the input jack for ground reference and a small grid stopper on the socket, like 27K - 33K. But only do this once you get V1a plate voltage up above 160v.

Another thing to do would be to replace the lower voltage diodes with either MPSA06 or 2N5401. So you have 18v zeners on one side of the switch and a more angry, less compressed sound on the other for modern sounds instead of the super low voltage diodes Ceriatone uses.

Anyway... yeah, go back to 10K dropper and your preamp voltages will come up where they need to be.

The other stuff you already did should be great.

Thanks 46&2!