Wire Wound Potentiometers Provide Excellent Tone Control On Bassman 200

The Bassman 200 valve amplifier has been a favourite amplifier for a select group of bass players since 1972 when they were first developed in a small factory in Marrickville, Sydney Australia. The have a power rating of 90 watts rms output and have an excellent warm tone and ‘punchy’ mid range sound. They have one common problem – scratchy potentiometers. The original carbon taper potentiometers were fine in the 1970′s and 1980′s but most Bassman owners have experienced their electrical deterioration over the last 20 years or so. This is caused by wear in the carbon track and the resultant crackling, hiss and noise makes the amplifier virtually unusable which is unfortunate given the quality of the overall build of the amplifiers.

Replacement Potentiometers

AW 3 watt Wire Wound Potentiometer

AW 3 watt Wire Wound Potentiometer

I have found a very workable solution to the noisy potentiometers by replacing them with a wire wound potentiometer from Resistor Specialists who are located just outside of Sydney in an industrial estate in Minto, N.S.W. Their range of AW series potentiometers have a nice linear taper, making it ideal for audio applications and the electrical rating of 500 volts (end terminal test) means that the potentiometer is ideally suited to valve circuitry where voltages in excess of 400 volts may be present.

Installation Into Bassman 200 Amplifier

I have found that the replacement of the ‘pots’ is fairly straightforward on the Bassman 200. I have replaced all of the following potentiometers with the AW potentiometers of the following values:

  1. Master Volume Control. I have used a 330 ohm value here and it works faultlessly
  2. Bass Tone Control. Here a 270 ohm works nicely – the original circuitry called for a 220 ohm potentiometer but i have found that a higher value gives a deeper bass range
  3. Treble Tone Control. A 560 ohm potentiometer works well for the treble control
  4. Pre Amplifier. Here i tried several values and have fornd that either a 330 ohm or 470 ohm potentiometer will work equally well.

Installation Guide

The potentiometers come with a standard ‘solder lug’ with a hole in the centre. I simply removed the mounting nuts from the original potentiometers and unsoldered the wires from the terminals of the old ‘pots’. It is then a simple matter of looping the cables (ensuring the wiper wire goes to the centre contact of the ‘pot’) into the terminals on the new potentiometers and soldering them. Then, simply install into the front amplifier control panel – easy!

Worth The Effort!

My Bassman 200 now performs fantastically with a wonderful sound that only wire wound potentiometers can offer, in my opinion. If you have any questions email me at rodbirch@bigpond.com. The AW series 3 watt wirewound potentiometers are available via http://resistorspecialists.com.au/