adapting a gas tank sending unit (potentiometer)

Yes. But that was 9 years later. In 59 they were still using "Vibrator Tubes" in car radios.
Totally used to those. My father put one in a 1962 vehicle. Half in the dash, half in the trunk.

I had a 73 vehicle that I put a Blaupunkt AM/FM/SW radio with the dial layed out in wavelength rather than frequency and later I built a solid state vibrator replacement external to the radio.

That was probably in the late 70's early 80's. At least until 1982.


Joined Mar 14, 2008
and later I built a solid state vibrator replacement external to the radio.
I also built a transistor replacement for a vibrator "tube" way back when.
As I recall it used two power transistors and a small signal transformer to create a multivibrator to replace the mechanical vibrator, which drove a step-up switching transformer that generated the high voltage B+ for the tubes (valves).
I mounted the circuit on a small piece of copper heatsink that fit inside the gutted tube of an old vibrator.
I plugged it into the radio in my '56 Chevy and, much to my surprise, it worked.
And there was no longer a soft "hummm" from the vibrator when the radio was on.


Joined Sep 30, 2009
I don't disagree - but, this is for a 1959 Plymouth!
OK, if this information was in the first post I missed it. Thought you were working for a company making the senders. Most cars of that era already have a voltage regulator in the housing of the gauge, to lower the chance of sparking in the tank.

They do make "ohm convertors", the street rod/hot rod guys use them.

EM Fields

Joined Jun 8, 2016
The circuit doesn't need to be anywhere near the gas tank, it could be under the dash, and powered by 12 volts. It just has to present 20 ohms to the gauge when the rheostat is at 10, and 225 ohms when the rheostat is at 125. I have no plans to touch the tank, or the sending unit.

So, can I get a reply from someone who can answer the question?
What does the load the sender sees look like?


Joined Sep 22, 2013
As best as I could tell, the sensor is fed from the ignition switch, thru the gauge and to the sensor, then to ground.

If you disconnect the sensor, put a 20 ohm resister at gauge input to ground, that will give you the designed full tank current. Replace the 20 ohm with a 225 ohm resistor, that will give you the off the post, zero (empty), current. We need to do this because with don't have info on gauge meter. (current range or possible shunt)

Once we know the designed current range, we can apply the appropriate voltage to supply side of the gauge, to regain the right current ratio. (with the defective resistance range)

Does this make any sense?


Joined Mar 14, 2015
@shortmort37 I say your problem can be solved with an op amp, a voltage reference and a few resistors! I agree that shunt across gauge can work too but I'm not comfortable with suggesting anything that increases current through sender! Anyhow it makes it easier for ppl to help if you're more responsive:)

PS fwiw I like suggestion of post 30 to compensate low sender resistance range by adjusting voltage:)
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Joined Apr 7, 2016
Late yesterday, I got an idea for the following circuits:


It is actually a simple bridge circuit, where T1 is the adjustable resistance that brings the bridge in balance.

If the idea is right, so should they showed component values double the sensor resistance value.

The schematic should be seen as a draft for the solution of the task, so the circuit is not ready for use in a car. There is a lack of protection on the supply and inputs of the amplifier and T1 must surely have some help of a medium power transistor that can get rid of the heat.