HMV Model 2404 Servicing

HMV Model 2404 has those black coloured electrolytic capacitors, which were notorious for leaking even back when this amplifier was newish, hence I would not hold much hope of them working today. Whilst listening to music on this amplifier and writing this very sentence, the strangest thing happened. There was a loud bang like a fire cracker going off and I found that one of the capacitors had exploded. It was a Callins 300 µF/25 V electrolytic capacitor. Hence my advice is that if you decide to use this amplifier, then it will first need a recap and proper service by a qualified and experienced electronic engineer.

Usually the power transistors require a nice large reservoir of charge nearby, and if there is insufficient power, then they struggle resulting in sound breaking up. Certainly when turning up the volume to full, there was a huge amount of distortion associated with insufficient power due to failed capacitors.

Here is a photo of an exploded capacitor if you have not ever seen one.

Before, the capacitor looked like this.

I replaced all the old electrolytic capacitors. Checking the old capacitors with a meter, I found that some were showing open, whilst others not storing much charge. In addition, I also discovered some open resistors, and one burnt open resistor.

Should you need to replace the power transistors, the AL102 may prove difficult to find, however occasionally some old stock usually appears on auction sites. There is also the AL103 which is very comparable and has a chance of working with some adaptation and modifications.

As you can see, the heat from the bulb has a tendency to burn the plastic, creating a smell of burning plastic.

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