Below, images of the power section of AC50 serial no. 1578. There are no dateable soldered-in components unfortunately - the original caps have been replaced. For the dates of components in the preamp, see this page.

The rectifier valve is certainly a replacement - from 1966. The two EL34s are from March 1965. It seems unlikely that the chassis remained on the shelf until mid 1965 waiting for valves to be fitted prior to sale. It generally took Mullard EL34s months to make their way from the factory into an amp, in any case.

More than likely the EL34s were replaced in the 1970s or 1980s when the preamp valves were renewed.

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Click as ever on the thumbnails for larger images.

GZ34 rectifier valve - date code B6A4 = Blackburn Factory, 1966, fourth week in January

Mullard EL34 XF3 - date code B5C4 = Blackburn Factory, 1965, fourth week of March

The second Mullard EL34

Tested bias voltage marked in pencil - "34" - and "K" which regularly figures in the power sections of early AC50 Mark 2s

Initials on the chassis - "JSM" ? - written before the wiring was put in.