Shaftesbury 519 Amplifier

[ppppenguin]

Good as Mullard 'mustard' capacitors are, the one you fitted is only rated at 400V and is not suitable for use in that position.... it needs a capacitor rated at 1000V.

While it was common practice to fit 1000V parts in this position back then this was recognition ofthe relatively low relaibility of older capacitors. Lots of the standard paper caps back then were only rated at 350V which really isn't enough.

In an ordinary radio or amp with HT under 300V I wouldn't worry about using modern 630V parts. Modern (which includes "mustard") 400V caps are likely to survive but not recommended.

If you disconnect the speaker and turn up the volume both the capacitor and output transformer will be at risk of overvoltage.

PS: At least in that design they fitted the cap across the transformer primary so if it goes short circuit the output tranformer doesn't suffer. The valve, rectifier and mains TX will all be unhappy. A lot of designs had the cap between the anode and 0V. Not a good idea as a short can destroy the output transformer, even though the output valve will be safe. I'd rather replace a valve than a transformer.