hiwatt custom 20 tube amp hum

Posted on Feb 4, 2014

A friend of mine bought a fairly new (only a couple of years old) Fender 60W combo off a guy he knew for £5. The original owner had taken it to three different repair shops, and been told it wasn`t worth repairing. I told my mate it couldn`t be much, and even told him EXACTLY what was wrong with it before he brought it me. I was dead right, it wa

hiwatt custom 20 tube amp hum
Click here to download the full size of the above Circuit.

nted anode load resistors, as valve amps always have. The electrolytic cap that filters the B+ for the preamp stage is probably dried out. The preamp stage probably has a B+ power that`s behind a second RC filter. +1 Anytime you have an old piece of equipment, suspect the electrolytic caps. They have very short life spans compared to most electronics. If you want to keep and use the piece, replace all the power supply filter caps. is the hum 60 or 120 hertz Is the power supply a full wave rectifier type If so, it seems the hum should have a 120 hertz fundamental if the filter caps are bad. Might have some heater to cathode leakage that many basic tube tester don`t catch. If the preamp tubes have the same number as later tubes, you can try interchanging them to see if the hum level changes.

Leave Comment

characters left:

Related Circuits

  • New Circuits



    Popular Circuits

    Solid-State Windshield-Wiper Delay
    Solid State Tesla Coil/High Voltage Generator Circuit
    Smoke Alarm Circuit
    Protection For Telephone Line
    most common emergency sirens circuits
    Low Frequency Antennas
    Fundamentals of Electrical Engineering and Monostable Multivibrator
    2G—10 Band Stereo Graphic Equaliser circuit diagram
    Digital tachometer schematic
    Battery over-discharge protection circuit diagram