How to determing parts from schematic (i.e. transformer)

[bill0287]

Let's say I wanted to build the amp in the attached schematic. How would I figure out a reasonable transformer to use based on the limited information given?

[Helmholtz]

Which of the 2 transformers?

[bill0287]

I am specifically looking at the "HV winding" item right now. But yeah, the output transformer has even less info.

[Helmholtz]

Most necessary info can be found in the tube datasheets.

OT should have a primary impedance around 8k and be rated for 6W minimum.

PT has 3 secondaries:
- 6.3V heater winding for 6V6 and 12AX7. Adding heater currents of 0.45A and 0.3A plus a little safety margin gives a current rating around 1A.
- The 2x 270V HT winding. The 6V6 has an idle current of 48mA, add ~1mA for the 12AX7. With fullwave rectification AC current roughly equals or slightly exceeds DC current, so the HT winding should be rated for 60mA minimum.
- The 5V heater winding for the 5Y3 should be rated for 2A.

[Mick Bailey]

I always then browse the Hammond catalogue for the best match. In this example the Fender Champ 5C1/5E1/5F1 has the same tube arrangement, so is easy to find.