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I have built an amp that is based on a 5F6A bassman. Something like this: https://taweber.powweb.com/store/5f6a_schem.jpg.
I have built it with only one channel so that I have one half of V1 available. I have used a switch that puts the second half of V1 as an additional gain stage between the first gain stage and V2 which feeds the tone stack. With this switch engaged the signal coming off the 270K resistor after the vol pot goes to the second grid of V1. The kathode is grounded via a 1K5 resistor and a 25µF cap. The signal coming fron the plate is decoupled via a .022 cap and then has a 1M resistor to ground and goes straight to the first grid of V2.
This boost sounds great but I get a lot of hum. Without the additional gain stage the amp is really quiet. I udes shielded wires for the long connections and star grounding throughout the whole amp. I do not think that it's a lead dress issue but rather a basic design mistake. ANy ideas? do I need to implement some kind of negative feedback to get rid of the hum? Any other ideas?
thanks!
I have built it with only one channel so that I have one half of V1 available. I have used a switch that puts the second half of V1 as an additional gain stage between the first gain stage and V2 which feeds the tone stack. With this switch engaged the signal coming off the 270K resistor after the vol pot goes to the second grid of V1. The kathode is grounded via a 1K5 resistor and a 25µF cap. The signal coming fron the plate is decoupled via a .022 cap and then has a 1M resistor to ground and goes straight to the first grid of V2.
This boost sounds great but I get a lot of hum. Without the additional gain stage the amp is really quiet. I udes shielded wires for the long connections and star grounding throughout the whole amp. I do not think that it's a lead dress issue but rather a basic design mistake. ANy ideas? do I need to implement some kind of negative feedback to get rid of the hum? Any other ideas?
thanks!