Thanks for the replies.
The bulb is 24V 50mA - almost the same as the original. Yes, this place used to be full of those illuminated switches
Phil, connecting a capacitor in series with the output (or, reducing the value of the existing capacitor) wouldn't help because the amplifier is clipping! Astonishing, but there really is that much bass boost. A high-pass filter ahead of the amplifier is obviously better, and indeed with this set, that's what pulling out the tone control does. I've attached a schematic of the volume/tone control for info (sorry about the quality, it's a photograph from the R&T Servicing book).
I ran a quick simulation - it ignores the power amplifier, but that is nominally flat (but I ought really find out what the LF -3dB point is). I had to make assumptions about how the volume control is tapped - I forgot to measure it before reassembly. The output is taken from the first tap - in other words the volume control has been turned around to coincide with the first tap. Also, the HF-cut tone control is assumed to be at the centre position.
As you can see from the green curve, there is an astonishing amount of bass boost - around 25dB between 1KHz and the peak at ~30Hz.
The yellow curve shows the response with the bass cut switch operated. There's still about 12dB, but this similar to other sets I've seen - you do need some... The peak moves up as well - now it's at ~60Hz. And the midrange dip is more pronounced. It definitely sounds better like this, although the plastic cabinet is still very resonant.
Finally, the schematic of the PSU - again, sorry for the quality. This isn't included in the downloadable sheet, so hopefully it's useful to have it here. Paul - very happy to produce a proper scan of this and email to you for inclusion in future DVD releases
Mark