Understanding and Selecting Chokes

HIGH VOLTAGE WARNING

Power supply chokes operate in high-voltage direct current (DC) filter networks (350V to over 500V DC). Filter capacitors store lethal electrical charges long after the amp is switched off. Always safely discharge power supply capacitors and verify 0V DC before touching internal chassis components.

Guitar Amplifier Chokes: Technical Guide & Calculator

Learn how power supply chokes work, estimate the current your build needs, and select replacement chokes from the Evatco catalog.

Choke Requirement Calculator

Estimate the DC current your choke must carry. Results are a guide only. Where possible, match the choke fitted to the original amp.

Minimum choke current rating -- mA Includes a 25% safety margin
Estimated voltage drop -- V DC Across the choke winding at the estimated current
Typical inductance 3H - 10H Power chokes. Match the original where possible

Parts in the table below that cannot meet your current or voltage are dimmed.

Evatco Choke Catalog & Cross-Compatibility

Chokes are often labelled by amp model (e.g. "Marshall Plexi choke"), but a choke can often be used in a different amp or a custom build if the specs suit it:

  • Current rating (mA): Must meet or exceed the DC current the choke carries in your circuit.
  • Inductance (H): Sets how hard the choke filters ripple, together with the capacitor after it. Typical values: Fender 4H, Marshall power chokes 3H to 5H (plus a 40H preamp choke), Vox 5H or 30H.
  • DCR (resistance): Controls voltage drop. Lower DCR means less voltage lost and less sag.
  • Voltage rating: The 153-159 series (such as 158Q, 159P, 159M) is rated 500V DC maximum. Check the voltage rating on the product page before using any choke in a higher-voltage supply.
Part Inductance Current DCR Fits / typical use
Hammond 194A 4H 50mA See product page Fender Deluxe, Deluxe Reverb, Vibrolux, Vibrolux Reverb
Hammond 194B 4H 90mA See product page Fender Bandmaster, Dual Showman, Pro Reverb, Twin Super
Hammond 194G 3H 250mA See product page Marshall Plexi
Hammond 194F 5H 120mA See product page Marshall later Mark II and 800 (50W and 100W)
Hammond 194C 40H 50mA See product page Marshall preamp choke (Plexi / JCM800)
Hammond 194D 5H 150mA See product page Vox AC30 reissue
Hammond 194E 30H 100mA See product page Vox AC30 reissue
Hammond 158Q 5H 150mA 105Ω General-purpose filter choke
Hammond 159Q 7H 150mA 100Ω Yorkville Bassmaster YBA-1 replacement; general purpose
Hammond 158M 10H 100mA 195Ω General-purpose filter choke
Hammond 159P 10H 125mA 155Ω General-purpose filter choke
Hammond 158L 15H 75mA 411Ω Low-current, high-inductance filtering (e.g. preamp supplies)
Hammond 159M 15H 100mA 256Ω Low-current, high-inductance filtering (e.g. preamp supplies, hi-fi)

Browse full specifications and order directly from our catalog:

View All Chokes on Evatco.com.au

How a Choke Works in Valve Amps

A choke (filter inductor) is a copper coil wound around an iron core. In most guitar amps it sits between the first filter capacitor and the screen grid and preamp supply, where it strips residual AC mains hum from the DC. In some designs it sits in the plate supply instead.

AC Impedance (Hum Blocking)

Inductors oppose AC ripple while letting steady DC pass with minimal loss. Together with the capacitor after the choke, this smooths the supply.

Voltage Drop and Sag

The choke's DC resistance drops some supply voltage. Higher DCR means lower screen and preamp voltage and a softer feel. Sudden current demands on loud notes are supplied by the filter capacitors, not the choke.