Chokes: What Are They? What Do They Do?
A choke is an iron core inductor used in the power supply of a guitar amp as a filtering element. Looking a lot like a transformer a choke only has two leads coming from the housing. They are designed to block AC while passing DC. Their purpose in guitar amp filter supplies is to smooth out the ripple in the rectified DC.
In some guitar amplifiers a high wattage resistor is used instead of a choke. A resistor in place of a choke saves money and to a certain degree manufacturing time. The drawbacks of using a resistor is there is more residual AC ripple in the power supply after rectification resulting in a little more background hum in your amp. One example is the 5E3 Fender tweed Deluxe. It does not have a choke in its filter supply.
Chokes have ratings of voltage, DC current ( measured in milliamps), resistance (measured in ohms) and inductance (measured in Henries). A typical choke for a 50 watt guitar amp is rated for about 500 volts and 50 milliamps. The resistance measures in the 250 ohm range and inductance between 10 – 20 Henries. The inductance of the choke coupled with the capacitance of the filter capacitors determine the bass response of the amplifier. A larger inductance value choke will have a better bass response than a smaller value choke. An amplifier with a power supply choke will have a deeper, crisper bass response than one that uses a resistor instead of a choke.
To sum up in simple terms using a choke in the filter supply the result is less background hum and cleaner, better bass response. Using a resistor manufacturers save time and cost and there is a bit more background hum and a looser bass response.