Tweet
Hello,
I found this forum while I was online looking for ideas on how to cure a loudly humming Vox AC30 with reverb. In March, there was a rather indepth discussion on getting rid of hum in probably the same model Vox amp as I am working on but I think my problem is comming from the phase invertor rather than the reverb. I pulled all the preamp tubes except for the PI and the power tubes and I get the hum(120 cycle). I pull the PI tube and the hum goes away. The filter caps look new and test O.K.(ESR, tolerance, and leakage). I also moved wires around with the amp on and I can not get the hum to change in sound. It sounds just like a bad filter cap. Whoever worked on this amp before me used a 50uf/30uf for the primary and screen supply and used a 16uf for the PI supply. Those values are lower than what my schematic says. Also, I have checked and rechecked for ground problems and bad connections. Any Ideas? Thanks.
I found this forum while I was online looking for ideas on how to cure a loudly humming Vox AC30 with reverb. In March, there was a rather indepth discussion on getting rid of hum in probably the same model Vox amp as I am working on but I think my problem is comming from the phase invertor rather than the reverb. I pulled all the preamp tubes except for the PI and the power tubes and I get the hum(120 cycle). I pull the PI tube and the hum goes away. The filter caps look new and test O.K.(ESR, tolerance, and leakage). I also moved wires around with the amp on and I can not get the hum to change in sound. It sounds just like a bad filter cap. Whoever worked on this amp before me used a 50uf/30uf for the primary and screen supply and used a 16uf for the PI supply. Those values are lower than what my schematic says. Also, I have checked and rechecked for ground problems and bad connections. Any Ideas? Thanks.