The power amp circuit is built using TIP35/36C transistor, the output stage is deliberately massive overkill. This ensures reliability under the most arduous stage conditions. No amplifier can be made immune from everything, but this does come close. The power amp is loosely based on the 60 Watt amp previously, but it has increased gain to match the preamp. Other modifications include the short circuit protection the two little groups of components next to the bias diodes (D2 and D3). This new version is not massively different from the original, but has adjustable bias, and is designed to provide a "constant current" output to the speakers. This circuit is achieved using R23 and R26. Note that with this arrangement, the gain will change depending on the load impedance, with lower impedances giving lower power amp gain. This is not a problem, so may safely be ignored. The figure is show the circuit;
The principle work and specification guitar power amplifier is power transistors will have an easy time driving any load down to 4 ohms. If you don't use the PCB, you can use TO3 transistors for the output stage. MJ15003/4 transistors are very high power, and will run cooler because of the TO-3 casing (lower thermal resistance). Beware of counterfeits though! There are many other high power transistors that can be used, and the amp is quite tolerant of substitutes (as long as their ratings are at least equal to the devices shown). The PCB can accommodate Toshiba or Motorola 150W flat-pack power transistors with relative ease, if you wanted to go that way. TIP3055/2966 or MJE3055/2955 can also be used for light or ordinary duty.
At the input end that is shown in the figure, there is provision for an auxiliary output, and an input. The latter is switched by the jack, so you can use the "Out" and "In" connections for an external effects unit. Alternatively, the input jack can be used to connect an external preamp to the power amp, disconnecting the preamp. The speaker connections allow up to two 8 Ohm speaker cabinets (giving 4 Ohms). Do not use less than 4 ohm loads on this amplifier. It is not designed for it, and will not give reliable service!
The principle work and specification guitar power amplifier is power transistors will have an easy time driving any load down to 4 ohms. If you don't use the PCB, you can use TO3 transistors for the output stage. MJ15003/4 transistors are very high power, and will run cooler because of the TO-3 casing (lower thermal resistance). Beware of counterfeits though! There are many other high power transistors that can be used, and the amp is quite tolerant of substitutes (as long as their ratings are at least equal to the devices shown). The PCB can accommodate Toshiba or Motorola 150W flat-pack power transistors with relative ease, if you wanted to go that way. TIP3055/2966 or MJE3055/2955 can also be used for light or ordinary duty.
At the input end that is shown in the figure, there is provision for an auxiliary output, and an input. The latter is switched by the jack, so you can use the "Out" and "In" connections for an external effects unit. Alternatively, the input jack can be used to connect an external preamp to the power amp, disconnecting the preamp. The speaker connections allow up to two 8 Ohm speaker cabinets (giving 4 Ohms). Do not use less than 4 ohm loads on this amplifier. It is not designed for it, and will not give reliable service!
