P1800 vintage plexi amplifier

2023 Shipping info: I am doing one final run of the P1800 amplifier kit – due to customer demand. I have a new version of the classic 18W-voiced amplifier, but it’s not quite ready to go yet. It will be a simpler and cheaper version, launching later this Summer (as soon as the parts arrive).

The P1800 guitar amplifier kit is the replacement for the very popular PP-18 amp kit. That means that at its heart is the same Dominator/18W tone. In adding features to the amp kit, I’ve made sure to keep the 18W signal path intact, so all of the same classic tones are available. The new features just add more tonal variety and more flexibility to the circuit. As a bonus, there’s also much more scope for tone tweaking.

Changes and improvements

The classic 18W circuit has two inputs, one Volume knob and a single Tone control for dialling down treble frequencies. It’s an all-time vintage classic, and the trick was how to add useful features but keep the 18W circuit’s tone. So, starting at the beginning of the signal path, here are the additional features of the P1800:

1. Cascaded inputs: The Hot input now runs the two preamp stages in series to provide more overdrive. The Normal input provides the classic 18W signal path.
2. Treble control: Exactly the same position and effect as the standard 18W amplifier’s Tone control, just renamed.
3. Bass switch: Off (down) when you want the pure 18W signal path; On (up) to add a bass tone control (especially useful when using the Hot input).
4. Bass control: A simple and effective way of controlling the amp’s bottom end to avoid ‘flubby bass’.
5. Output switch: A four-position switch that controls the signal to the power valves. SE to drive just one power valve for single-ended output; PP driving both power valves for the classic 18W push-pull tone; PP+ just like PP, but with a smoother tone; Mute to replace the conventional Standby switch.
6. Power: This controls the VCB circuit and lets you dial the fully-cranked output down to well under 1W for quiet home use

Ease of building

The P1800’s new features add some extra complexity compared to the old PP-18. On a complexity scale of 1-5, the P1800 rates as a ‘3’ (where the original PP-18 was a ‘2’ and the WF-55 is a ‘1’, for example). The online construction manual shows how to build the amplifier step-by-step. If you are recycling an old amplifier chassis, you can buy the kit without the chassis and panels and save a fortune (see options on the right). Likewise, if you already have valves, there’s another significant saving available if you buy the kit without valves.

P1800 specifications

• All-valve signal path
• 0-18W output
• single-ended/push-pull output
• Hand-wired turret board
• Volume and Power level controls
• Treble and Bass controls
• 8/16 ohm speaker outputs
• 120/240V or 220/230/240V mains