what those 330uF caps next to switch channel transistors for?

[otto]

In the schem
http://www.drtube.com/schematics/marshall/4210.gif
what are those 330uF caps next to switch channel transistors for? Are they to 'soften' the switch or have they anything to do with tone?
In my amp they are 25 years old (electolytic), everything works well, I don't know if replacing them could improve tone ...

[Enzo]

That is a filter cap. Look at the two diodes to its right. They come from the 6VAC heater power supply. Those two diodes rectify the AC and the 330uf filters it for the switching circuit. That is all it does.

It is not in the signal path, but if it gets weak, then that low DC voltage will be hummy, and that could be passed into the signal path by way of one of the transistors in the channels.

Or are those the ones you meant? The transistors up by the volume controls are mutes. When they are on, they put that 330uf cap across the signal path. That pretty much is a short circuit for audio. SO it is grounding the signal at that volume control wiper. In other words the transistors there turn OFF the unwanted channel. If those were weak, then they would not turn off the non-selectrd channel as well. In other words, the gain channel would leak through into the clean or the clean into the gain.

[otto]

Thanks Enzo. I was speaking of the 2nd caps you wrote about, the ones next to transistors in tube stages v1 and v2. You are confirming what I supposed. I've no problems with unwanted channels. When one channel is on the respective 330uF cap doesn't work because it's not connected to ground. It acts as a sort of dumper when switched to ground.
Thanks