Walker Posted October 16, 2013 Share Posted October 16, 2013 (edited) [b]Amp fuse – looking at schematic, can I replace 63ma with 100ma fuse?[/b] I’m just trying a few obvious things before I send my Ampeg SVT-IIP preamp off to a tech (resoldering a few joints, new valves, etc). The bright input rapidly fluctuates in volume. During my poking around, I found that one of the fuses (see the attached schematic – bottom left corner) has blown, the amp still works, so not sure what the fuse does. To be honest, this is the first schematic I’ve ever looked at and I’m really enjoyed trying to decipher it! I’ve had no joy trying to find an imperial sized (6.3mm x 32mm) 64ma (1/16amp) 250v slow blow fuse. [b]My question is: looking at the schematic, would it be really stupid to drop in a 100ma slow blow in instead?[/b] As the amp still works, I’ve assumed the fuse protects against the switchable voltage selector being in the wrong position? Or is that just another newb assumption? Thanks for your help. [url="http://oi42.tinypic.com/4q5gh.jpg"]http://oi42.tinypic.com/4q5gh.jpg[/url] Edited October 17, 2013 by Walker Quote Link to comment Share on other sites More sharing options...
Walker Posted October 17, 2013 Author Share Posted October 17, 2013 Schematic now fixed in OP. Sorry for that. Quote Link to comment Share on other sites More sharing options...
BanditSid Posted October 17, 2013 Share Posted October 17, 2013 (edited) [font=arial,helvetica,sans-serif][size=5][sup]If it is the lower fuse (fuse 2) then it has no effect on the amp operation when you are configured for 230 volt operation, it is there to power the lower primary coil on the transformer when the amp is in 115 volt mode. [/sup][/size][/font] Edited October 17, 2013 by BanditSid Quote Link to comment Share on other sites More sharing options...
Walker Posted October 17, 2013 Author Share Posted October 17, 2013 Thanks very much indeed, that's really helpful. Quote Link to comment Share on other sites More sharing options...
Walker Posted October 17, 2013 Author Share Posted October 17, 2013 So looking at the top left corner of schematic - the bright input, is it just the 100k resistor and the .0047 cap that makes up this 'bright' circuit, or does it go deeper into the schematic? So if those two components are replaced, could that maybe solve my fluctuating volume issue? I've got new tubes coming too. Thanks Chris Quote Link to comment Share on other sites More sharing options...
BanditSid Posted October 17, 2013 Share Posted October 17, 2013 Does the gain only fluctuate on the bright input, is it stable on the normal input ? If so I would say there is either a problem with input socket or a dry joint around the socket or the parallel capacitor/resistor network.....it is unlikely that they are faulty and need to be replaced. Quote Link to comment Share on other sites More sharing options...
Walker Posted October 17, 2013 Author Share Posted October 17, 2013 That's exactly right - only the input socket. Thank you, at least I can point a technician in roughly the right direction! Thanks again for your help, really appreciated. Quote Link to comment Share on other sites More sharing options...
Walker Posted October 31, 2013 Author Share Posted October 31, 2013 Sorted! As you suggested, a couple of dry solder joints. Now as good as the day it came off the production line (no, better in fact!). Thanks all for your help. Quote Link to comment Share on other sites More sharing options...
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