http://www.ozvalveamps.org/challenge.html | Created: 10/12/09 | Last update:
This is the original Challenge, c1950.
Mielnik also produced an unrelated amp under the Challenge marque some time later.
Single-ended (Class-A) output stage with the output transformer mounted on the speaker. This encapsulated style and mounting of output transformers are a good indication of early amplifiers as it went out of fashion around the early 1950's.
The preamps (left) are 6AV6's which are a single triode-double diode popular in early domestic radio receivers. In this application they are each equal to half a 12AX7 section, and the diodes are unused.
The next valve is the output, normally a pentode, possibly a 6BM8.
The rectifier (nearest the power transformer) is seriously blackened internally by electrons striking the glass and shows it has been in service a long time, however it does not mean it is faulty, just old.
The single top-cut tone control, common to both channels, doubled as the mains power switch.
Apart from the “Nicholson's” label on the front, the power transformer gives it away as a Sydney build.
Click on key images to see full sized image.
Source: Peter G Field
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