Pow_22 Posted December 12, 2011 Share Posted December 12, 2011 Im taking my SC in for a full service soon but as it hadnt been fired up for a few weeks i thought id give it a blast this weekend. I set it up in the spare room and flicked it onto stand by while i had a brew and let the valves all warm. Came back in, plugged the bass in and flicked on the power......nothing happened, no noise, no nothing. I looked in and all the EL34's were glowing niceley....i couldnt fathom out what was wrong. Then i checked the back......id put the jack lead for the cab into the Effects Loop input and not the Cabs socket. I quickly switched it off (even tho im a valve newbie i know never to turn on an amp with no load). Anyway, i re-connected the lead correctly and tentively switched it all back on. The amp is working fine now but having had it on standby with no load for a good 20 mins im wondering what damage i could have done to it? Its going in for a service soon and i may well be taking up Mr Foxton on a great offer of some EL34's but just wondering what damage i could have done to the amp Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted December 12, 2011 Share Posted December 12, 2011 I think it has shorting jacks so if nothing was plugged into them (as opposed to a lead plugged in with nothing on the other end) they'd have a low impedance load, which is supposed to be happy. Is Bruce competing with me on valve sales then? Quote Link to comment Share on other sites More sharing options...
Pow_22 Posted December 12, 2011 Author Share Posted December 12, 2011 Haha of course i meant you Oli! So effectively i had the lead plugged into the cab socket on the back of the amp but not had the other end attached to anything then that wouldve been bad - as opposed to basically having the amp completely unattached? Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted December 12, 2011 Share Posted December 12, 2011 Probably, the actual mechanism of an unloaded amp self destructing is a bit hard to pinpoint. The idea of shorting jacks is that a dead short is better than totally open. Quote Link to comment Share on other sites More sharing options...
SebCarr Posted December 12, 2011 Share Posted December 12, 2011 [sup]Should be fine. On Standby the power tubes heaters will be running, but they shouldn't be seeing any B+.[/sup] Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted December 12, 2011 Share Posted December 12, 2011 Doesn't apply to all amps though, because the 'standby' switch doesn't always do the same thing. Pretty sure it does on the Sound City though. Quote Link to comment Share on other sites More sharing options...
SebCarr Posted December 12, 2011 Share Posted December 12, 2011 Yes, and you also see all sorts of shonky mods to valve amps (and ground wires disconnected in 50 year old amps with 3-400+ volts floating around in a metal chassis... eek!) I had a quick look at a couple of SC schemos and they do isolate B+ on standby Quote Link to comment Share on other sites More sharing options...
bertbass Posted December 12, 2011 Share Posted December 12, 2011 No speaker on a valve amp normally means burnt out output transformer very quickly. You're very lucky. Quote Link to comment Share on other sites More sharing options...
umph Posted December 12, 2011 Share Posted December 12, 2011 [quote name='bertbass' timestamp='1323706754' post='1466059'] No speaker on a valve amp normally means burnt out output transformer very quickly. You're very lucky. [/quote] not really if he didn't take it out of standby it wont hurt it. Quote Link to comment Share on other sites More sharing options...
obbm Posted December 12, 2011 Share Posted December 12, 2011 From the OP's first post my interpreation of [quote]flicked it onto stand by while i had a brew and let the valves all warm. Came back in, plugged the bass in and[b] flicked on the power[/b]......nothing happened,[/quote] is that it was fully powered with no speaker attached. Hope it's OK. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted December 12, 2011 Share Posted December 12, 2011 Also if plugged into fx loop output, doesn't that cut signal to power amp section? Dunno if signal is necessary. Quote Link to comment Share on other sites More sharing options...
Big_Stu Posted December 12, 2011 Share Posted December 12, 2011 [quote name='bertbass' timestamp='1323706754' post='1466059'] No speaker on a valve amp normally means burnt out output transformer very quickly. You're very lucky. [/quote] [quote name='umph' timestamp='1323707062' post='1466064'] not really if he didn't take it out of standby it wont hurt it. [/quote] OP says the bass was plugged in, but doesn't say he played it so far as I've noticed; if he'd hit a note it & had it out of standby it could have been curtains; I've known some folk get away with it & put it down to superior Partridge tranny build. But I've been reliably informed by some valve amp techs that an amp without cabs plugged in isn't in any danger until a load is put on the amp - ie. you try to play through it. It's been covered umpteen times on here & other forums. Quote Link to comment Share on other sites More sharing options...
umph Posted December 12, 2011 Share Posted December 12, 2011 [quote name='Big_Stu' timestamp='1323715499' post='1466203'] OP says the bass was plugged in, but doesn't say he played it so far as I've noticed; if he'd hit a note it & had it out of standby it could have been curtains; I've known some folk get away with it & put it down to superior Partridge tranny build. But I've been reliably informed by some valve amp techs that an amp without cabs plugged in isn't in any danger until a load is put on the amp - ie. you try to play through it. It's been covered umpteen times on here & other forums. [/quote] This is true. pretty much the only way you blow output transformers Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted December 13, 2011 Share Posted December 13, 2011 I've heard that some amps can go into oscillation when unloaded which would have the effect of blasting signal. Mine was prone to oscillation because of a duff resistor. Quote Link to comment Share on other sites More sharing options...
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