Item nr.

Belco MG100 Audio generator

Decent measurement instrument.

Data for Belco MG100
ProductionJapan, 1970.
BandsDial 18-220Hz; Switch 1x, 10x, 100x, 1000x.
PowerAC 230V, 2.3W.

The Design

The frequency is controlled by an RC circuit, as can be seen from the large variable capacitor inside (plus resistors near the band switch). Advantage of RC circuits over LC circuits is that the frequency control range can be much larger: a variable capacitor has a control range of 1 to 10 usually, making 1 to 3.1 the maximum ratio of an LC tank (with fixed L the frequency is related to the square root of capacity). The frequency of an RC circuit is inversely proportional to C, so the control range can be 1 tot 10 in a single band.

Obtained7/2013 from NVHR Swap meet.
Sound samplePLAY SOUND   Connect a small speaker, tune the frequency dial from 600 to 1200Hz and flip the wave form switch from sine to block; this is what you'll hear.

This Object

Probably I won't need or use this item very often, but it was offered at the Swap Meet at a price I didn't want to refuse.

You can open the unit by removing the four corner screws in the front. The largest part of the space inside is filled with the air capacitor, then on one side you find a small circuit board with a power supply, and on the other side a board with the oscillator circuit.

Searching the internet for a schema didn't give a result for me and neither for several other people. Here is a schema of a similar machine, that might give you an idea also of how the Belco works.

Part of Gerard's Radio Corner.
Generated by SiteBuilder on 4/6/2020 by Gerard (g.tel@uu.nl)