Custom amp build w- baritone guitar in mind
Posted: Thu Feb 07, 2008 2:09 pm
I'm going to try to build this soon. I'd appreciate it if anybody had some suggestions or insight. I know a good amount about tube amps, but I could sure use help.
for the speaker, I got a 15" 75W blue dog ceramic speaker from ted weber. Similar to the vox blue speakers but much more power handling and lows.
The circuit is mainly based off of two amps right now, a vox AC50 and blackface bassmans.
The first channel Is very similar to an AC50 preamp, with a couple of differences. It starts with a common cathode amplifier with a 820 ohm resistor. This has less gain than a normal fully bypassed stage, however I did that so I could add a treble boost switch which adds a small capacitor in parallel with the resistor boosting frequencies above about 500hz an extra little bit. The 820 ohm resistor has a slightly smaller effect (gain difference) than a 1.5K resistor would.
Next is a cathode follower into a Vox AC50 Tone stack. However, at the end I added a 1M volume pot, this shouldn't signifcantly change the impedance of the circuit too much. I probably won't add a bright cap.
The next stage is a recovery stage. I might move the volume pot after this if I think I need it instead there. This is then coupled with a .022uf cap into a 220K resistor, than to an additional gain stage. I might make the tonestack more like the classic plexi if this doesn't work out too well.
The other channel is straight off of most blackface fenders "normal" channel, with the addition of a rotary switch which selects 3 different values of capacitors on the tone control, switching between .022, .047, and .1uf. These change the bass response of the circuit. In a blackface AA864 bassman amp, the value is .1uf w/ a switch to make it .2uf. In a super reverb, it's .022, in a twin, it's .047. I'm not sure exactly how much this will change the response overall, but I think it's an easy thing to do so I might as well. I have a fixed 6800K resistor in there right now, I might turn that into a mid control instead.
This is coupled with a .022uf cap into a 220K mix resistor into the same third stage as above.
This third stage is just like the common third stage on the ab165. I think I am going to keep the 470K feedback resistor, but I'm going to change the input resistor to 1M, giving a little less feedback, but I'm not sure.
Finally, this is all fed into a long tailed phase inverter (12at7 or 12ax7) configured with a presence control, like the classic bassman. The feedback resistor will be increased to 56K. Coupling capacitors after will be .047uf into the power stage.
The power stage will be 6l6s probably, but kt66s or el34s are an option. The output transformer will be a hammond 1650N, rated for 60W output. I might go with something a closer to 50 as I should be able to put out 60W or more with the voltages on this weber power transformer, and saturating an output transformer. The weber power transformer should be fine with this given the specs and solid state rectification.
for the speaker, I got a 15" 75W blue dog ceramic speaker from ted weber. Similar to the vox blue speakers but much more power handling and lows.
The circuit is mainly based off of two amps right now, a vox AC50 and blackface bassmans.
The first channel Is very similar to an AC50 preamp, with a couple of differences. It starts with a common cathode amplifier with a 820 ohm resistor. This has less gain than a normal fully bypassed stage, however I did that so I could add a treble boost switch which adds a small capacitor in parallel with the resistor boosting frequencies above about 500hz an extra little bit. The 820 ohm resistor has a slightly smaller effect (gain difference) than a 1.5K resistor would.
Next is a cathode follower into a Vox AC50 Tone stack. However, at the end I added a 1M volume pot, this shouldn't signifcantly change the impedance of the circuit too much. I probably won't add a bright cap.
The next stage is a recovery stage. I might move the volume pot after this if I think I need it instead there. This is then coupled with a .022uf cap into a 220K resistor, than to an additional gain stage. I might make the tonestack more like the classic plexi if this doesn't work out too well.
The other channel is straight off of most blackface fenders "normal" channel, with the addition of a rotary switch which selects 3 different values of capacitors on the tone control, switching between .022, .047, and .1uf. These change the bass response of the circuit. In a blackface AA864 bassman amp, the value is .1uf w/ a switch to make it .2uf. In a super reverb, it's .022, in a twin, it's .047. I'm not sure exactly how much this will change the response overall, but I think it's an easy thing to do so I might as well. I have a fixed 6800K resistor in there right now, I might turn that into a mid control instead.
This is coupled with a .022uf cap into a 220K mix resistor into the same third stage as above.
This third stage is just like the common third stage on the ab165. I think I am going to keep the 470K feedback resistor, but I'm going to change the input resistor to 1M, giving a little less feedback, but I'm not sure.
Finally, this is all fed into a long tailed phase inverter (12at7 or 12ax7) configured with a presence control, like the classic bassman. The feedback resistor will be increased to 56K. Coupling capacitors after will be .047uf into the power stage.
The power stage will be 6l6s probably, but kt66s or el34s are an option. The output transformer will be a hammond 1650N, rated for 60W output. I might go with something a closer to 50 as I should be able to put out 60W or more with the voltages on this weber power transformer, and saturating an output transformer. The weber power transformer should be fine with this given the specs and solid state rectification.
