philips: Philips 2502;

The valve F215 is very difficult to find it. So I decided to replace it with E433. But there is a difference in heating voltage: for F215 is 2.5V, 1.5A and for E438 is 4V, 0,8A.

So I decided to build a small transformer from 2.5V to 4V. Calculating, I obtained: Q=2.5 cm², n1=20 turn, 1 mm in diameter and n2=68 turn, 0.6 mm in diameter: n1 is connected to the transformer and n2 is connected to the filament of E438.

You can see in the picture attached. The only difficulty is a good shield for the transformer to have no influence in the audio circuit.

MH: I took the liberty of rendering this text anew for legibility. Regards, Mark

Attachments:

• The transformer (26 KB)
• Conection to heater (35 KB)

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