0-190-275V 20W frame transformer

Choice of output voltages; create an amp with switchable B+!

2021 UPDATE: This TX is used in Amp Maker kits and has also been a popular choice for other amp builders. It’s no longer available to buy from Amp Maker, but you can order it directly from the TX maker, Primary Windings Ltd


This is the frame-style of the 0-190-275V transformer that’s been powering PP-18 and P1800 and Double Six amplifiers for over 10 years. I am now discontinuing it, so it’s available at a low price. As with the drop-through type, you get:

  • 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) or VVR 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 a 120/240V (US/UK) version (220/230/240V version sold out).

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