Firing up an old valve amp of unknown provenance

[Simon Barden]

Ther3 really shouldn't be an issue with 230v and 240v. The UK is nominally 230V now, but unless you are supplied by a recently replaced substation, we'll still get 240v or more, not 230v. And CE marked equipment (like the Marshall should be) is designed to work on 230v +10%/-6%. So should work OK from between 216v up to 253v.

680V sounds weird, as 450vDC at 230v should give a maximum of 469v DC at 240V. The main smoothing caps are rated at 500VDC, so they would have all blown up at 680v. 680v sounds more like the peak AC voltage you'd get before any rectification and smoothing. The schematics I found on line didn't give any test voltages, which isn't very helpful.

[DrNomis_44]

Ther3 really shouldn't be an issue with 230v and 240v. The UK is nominally 230V now, but unless you are supplied by a recently replaced substation, we'll still get 240v or more, not 230v. And CE marked equipment (like the Marshall should be) is designed to work on 230v +10%/-6%. So should work OK from between 216v up to 253v.

680V sounds weird, as 450vDC at 230v should give a maximum of 469v DC at 240V. The main smoothing caps are rated at 500VDC, so they would have all blown up at 680v. 680v sounds more like the peak AC voltage you'd get before any rectification and smoothing. The schematics I found on line didn't give any test voltages, which isn't very helpful.

I agree, I'm not sure exactly why I was measuring 680V DC HT, maybe I made an error, or something, good job I was careful enough to ensure I didn't get a potentially fatal electric shock, anyway, the tech managed to fix my Marshall MA100C and it hasn't blown the main HT fuse yet.....touchwood.


Here's a link to a page on the Freestompboxes.org Forum, where the tech, blackbunny, explains exactly what he did to fix my Marshall MA100C amp (scroll down to the bottom of the page):

https://www.freestompboxes.org/viewt...2202&start=120