We found this circuit in a 1978 publication. The diodes can be 1N4002 or 1N4004 and the secondary of the transformer can also have voltages slightly higher than 6 + 6 V. The instrument can also be a 200 uA microammeter which is more common.

We found this circuit in a 1978 publication. The diodes can be 1N4002 or 1N4004 and the secondary of the transformer can also have voltages slightly higher than 6 + 6 V. The instrument can also be a 200 uA microammeter which is more common.