I specced this power transformer to be very flexible, able to run medium-power single-ended amps and low-power push-pull amps. The first step was to choose high voltage windings to suit a range of projects. I looked at popular amp projects and chose the following:
* The 0-190V winding produces around 260V when rectified - great for EL84-based amps. There's the full 160mA available, so you can run a pair in push-pull, parallel SE or even in stereo.
* The 0-275V winding gives typically 360V when rectified - designed for octal power valves (EL34, 6L6, etc) in more powerful SE amps (15W or so). This also has 160mA available, so it's also perfect for push-pull amps with lower-power valves, such as the EL84 and 6V6.
* The 190-275V winding is also available, and gives around 115V when rectified. This is a 'freebie' - a side effect of the two main values I chose - but it adds a really useful option to use in amp projects...
...Switchable B+! With these asymmetrical windings, there are three combinations available to run into the rectifier bridge. This means you can use a 3-position rotary switch to get a switchable B+ supply in your amp. With the ratios given you get:
* Full power from the 0-275V winding
* Half-power from the 0-190V winding
* 1/10th power from the 190-275V winding
It's like an ultra-simple version of Power Scaling (see Kevin O'Connor's London Power Website for the cost of a switch! With 3A at 6.3V available for heaters, this is a very flexible transformer for amps up to 18W or so in output.
Dimensions & info It's 78mm wide, 70mm deep and 64mm tall, with standard solder lugs for all primary and secondary connections. It's available in two versions:
* Lay-down style, to drop through a rectangular cut-out in the chassis (such as that on AC04 small and AC02 medium chassis). The rectangular cut-out should be 54x49mm, and the four 4mm mounting bolts are on 64x51mm centres. This type has a dual 120/240V primary winding.
* Frame type to fit above the chassis. This type has 220/230/240V primary which gives a better choice of wiring options for use across Europe. It has four M3.5 mounting holes on 64x51mm centres, and fits on the AC05 medium chassis. This version comes with a pair of insulating covers that fit on over the solder lugs (shown right). As M3.5 hardware isn't easily available, it ships with four sets of M3.5 hardware for mounting.
Like Amp Maker's other transformers, PT03 is made in England by a traditional and long-standing transformer winding company.
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The lay-down type drops through a reactangular hole in the chassis
This places all solder lugs safely inside the chassis for direct wiring to the amplifier circuit
The frame style of transformer (above) comes with touch-proof insulating sleeves (below) to cover the solder lugs, and you run the wires through a grommet into your chassis
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