The original Fairchild 670 limiter used a saturation transformer to provide a harmonic free stablized supply for the 6386 heaters in the gain reduction stage. Supply stablization for the heaters are one of several areas that help to maintain a stable signal level at the output stage. Too little heater voltage and the signal drops, also reducing the performance of the tube, and too much voltage and the signal increases. Consequently signal level and performance at the o/p of the gain reduction stage are connected to these key areas. The CVT (ferro) uses the unique principle of ferroresonance: the operation of a transformer in the region of magnetic saturation. When the iron core of a transformer is in saturation, relatively large changes in winding current results in very small changes in magnetic flux. Winding current and magnetic flux are proportional to the input and output voltage, respectively. This means that relatively large changes in input voltage result in small changes in output voltage: this being the fundamental purpose of an automatic voltage regulator.

simplified schematic

Analoguetube now supplys a direct replacement CVT that is specially designed for your Fairchild 670 and is a direct replacement for your old and tired regulation transformer! All transformers are supplied with easy fitting instructions and teflon lead-out wire.


Note: The AT-101 is fitted with new CVT transformers as standard.

There are a couple of options available:

Option 1

1. Fitting semeiconductor technology (which has made some huge advances in regulation since the 50's) offers one solution, it provides a simple linear regulated supply with a very low noise heater voltage and slow rise time during switch on. These linear supplies are capable of providing 5 amps - enough current to comfortably run eight 6386 tubes.

Option 2

2. Fitting a replacement CVT transformer for the old Sola transformer is now available. Your new transformer has been designed specifically for correct regulation with a 2.8amp load when all eight 6386 tubes are running. The CVT is supplied with a standard capacitor and has been developed for US and EUK applications. It will run at 120vac or 240vac with 60hz or 50hz operation.



The graph below shows a simplified version of a magnetization curve to demonstrate the functional concept of this transformer. In the saturation region of the curve (red), a large change in input voltage results in a small change in output voltage.