Peter Avgeris Exotic Double C Core Interstage Transformers

This is a newly manufacured pair of Exotic Double C Core Interstage Transformers. They are proposed for vacuum tubes on input or driver stages of Single Ended audio amplifiers. These transformers have been exclusively designed and manufactured for the best Directly Heated Triode tubes that have internal impedance in the range of 3 to 10 kOhms, like american type 26, Telefunken RE084, RE134, etc.

Typical comparable applications include Interstage Transformers of primary impedance around 10 or maximum 15 kOhms but this is a very bad design for tubes having internal impedance in the range 3-10 kOhms. Single Ended aficionados know that the best DHT tubes ever made have Rp that lie in this range, so these transformers have been designed exclusively for them!

The load linearity in the frequency domain and the frequency response obtained through these transformers is spectacular, no comparison to any other product regardless of price, market status, etc., something that is clearly seen through the square wave response. With these transformers we achieve maximum gain, minimum distortion, ideal load linearity in the frequency domain and spectacular frequency response!


The cores are made of silicon steel cold rolled grain oriented ferromagnetic paterial with 0.23mm ribbon thickness. Coil formers are hand assembled, made of carton pieces precision cut on a laserjet machine. Mounting brackets are also cut from baltic birch plywood.
Nominal primary impedance is 47kOhms
Primary inductance (measured at 1V RMS) is measured in excess of 300 Henries!
Primary and secondary DCR is 900 ohms (bifilar wound).
Turns ratio is 1:1
Maximum DC voltage for primary coil is 350 Volts due to the nature of winding.

Frequency response:

With primary impedance 600R, 10Hz@-0.2dB, 600kHz@-1dB, 1.2MHz@-3dB
With primary impedance 5k, 10Hz@-0.2dB, 170kHz@-1dB, 360kHz@-3dB
With primary impedance 10k, 10Hz@-0.4dB, 95kHz@-1dB, 210kHz@-3dB