113
Item nr.
Electronic voltmeter, AC 10mV to 300V.
| Production | The Netherlands, 1950. |
|---|---|
| Bands | Measures AC voltage from 20Hz to 1MHz.. |
| Tubes | EZ2 EF40 EF50 EF51 ECH21. |
| Cabinet | Steel. Size 32x25x14 cm. |
| Power | AC. |
| Documents | Service documentation. |
To make it all work at lab quality, a few sophisticated circuits were added. First there is a large amount of negative feedback in the amplifier to get a flat frequency response (within 2%!!) from 20 to 1000000 Hz. The feedback also eliminates the influence of mains power drift.
Before each measurement the meter is calibrated. The reference voltage is taken from the heater supply through a bridge containing some resistors and a light bulb. Increase in line voltage heats up the bulb, which increases resistance and changes the equilibrium of the bridge. This cancels out line voltage fluctuations: the reference voltage changes by no more than 1% when the line voltage changes between 198V and 242V (the nominal 220V +/- 10%).
Of course the various sources of errors accumulate. An overall precision of 5% should be obtained.
| Obtained | 12/1998 from NVHR Swap Meet. |
|---|---|
| Condition | 8. |
| Disposed | Sold 4/2001. |