In a four-tube amp, pin 3 on both tubes will be connected with a wire.
On a typical octal tube, this will be pin 3. Connect the other end to that same tube's plate connection (Fig 2). Next, connect a wire to one of the switched terminals on that same pole of the switch. Connect the other end to the screen grid resistor(s) of the right tube(s) (Fig 1). Now we should be ready to wire the switch.įirst, connect a wire to the common terminal of one side (or pole) of the switch. In a four-output tube amp, leave the right pair connected to each other and the left pair connected to each other and disconnect the wire in the center connecting the right pair to the left pair. In a two-output tube amp, disconnect the wire connecting the resistors. In many amps, these screen grid resistors may be tied together with a wire or solid buss wire. We will be connecting this to the switch. This will typically be a wire coming from the B+b section of the power supply. Leave the resistor attached to the tube socket and disconnect whatever is connected to the other side of the resistor. In the case of a typical octal tube, this will be pin 4 and will usually have a 470 ohm or 1K ohm resistor attached. The common terminal of each side will connect to the tube screen grid pin. One set of contacts (or pole) of the DPDT switch will be used for one side of the push-pull output stage and the other pole for the other side. No extra holes and completely reversible.
Toggle switch vox ac30cc2 install#
Since this amp would probably not be used with more than one cabinet, I chose to install a rotary version in place of one of the speaker output jacks on the rear panel. The first thing you'll need to do is install a DPDT (double pole/double throw) switch in the amp. This rotary half-power switch was installed in an output jack space for minimal invasiveness and easy access, and can be easily undone. The example here is a Marshall JTM45 Plexi reissue. This is actually the same circuit you will find in the Marshall 25 Silver Jubilee amps labeled as high and low power.
Toggle switch vox ac30cc2 mod#
This mod can be done in most any Fender or Marshall type amp, or any amp which utilizes a pentode-style output tube, such as a 6L6, E元4, 6V6, 6550, KT66, KT88, etc. When it is in half-power, or triode, mode, the output tubes are wired to run in a configuration that results in a reduction of power.
Toggle switch vox ac30cc2 full#
When the switch is in full power, or pentode, mode, the amp is completely stock. This will work with amplifiers that have two or four output tubes and will reduce the power by approximately 40 percent or more. Well, you could install a pentode/triode switch. Plus, this option only works with amplifiers that have four output tubes, so what do you do if you have an amplifier with only two output tubes? This, however, theoretically changes the output impedance by 50 percent, and in the case of most Fender amps, there's no option to select a different output impedance, so you're stuck with a mismatch. In one switch position, the amp will be completely stock, and in the other, the output should be reduced.