Tube Amp Archive

I have got a new Covid lockdown project, just the preamp section of the Mesa Boogie Mk I for the Santana sound. I have collected as many schematics as I can, but there are inconsistencies so I would be grateful for advice. On input 2, the top input shown, is the 220k to ground resistor hard-wired or...

I am waiting for the choke to arrive. In the meantime I’ve removed the 1k resistor. Looking at the original low pass filter of 1k with the 33uf capacitor, I get a ceiling of 4.82 Hz (using an online calculator). With the choke, this would increase to 12.39 Hz, so I have paralleled a 47uf capacitor t...

Thanks for the offer but I’ve already ordered the choke. It only cost £20, so I’ve spent £44 in total for the back to back transformers and choke. It is also a learning process for me and I’m in Covid lockdown so it keeps me busy. If I can get close to 255V on the plate voltage, I will be happy. Tha...

Thanks, I need to re-bias the EL84. I’ll do this when I fit the choke. It works but it is running too cold. I just tack soldered the cathode resistor in. I am going to use a 5 watt potentiometer to adjust the bias. I used this schematic but it isn’t complete. Fortunately I found a good photo of an o...

I have just built a clone of the Vox AC4. To save money, I used back to back power transformers. I used a full-wave diode bridge rather than a tube rectifier. I am getting good voltages for the heater supply to an EF86, 12AX7 and EL84. The problem I have hit is that the plate voltages are too low. O...