Valve amp problem

[john_the_bass]

Took my amp to a gig last night - I have a Laney LC30-II - a 4xEL84 powered 30w 112 [b]guitar[/b] combo (ok so it's sort of the same!). Plugged it in, switched it on and nothing - no lights, hum, anything.
So this morning I had a look at it, took the T315mA fuse out (HT fuse, whatever that is). It didn't look blown and I don't have a voltmeter, but the man at Maplins did and said it hadn't blown. I went home and discovered the other mains fuse (underneath the IECC socket) - a T630mA 20mm fuse, which had blown.

What's happened is this - at some point, prior to me buying the amp, the speaker cable appears to have been cut and connected back together with one of these.:



The block has come into contact with one of the output valves, melted through the insulation to the metal cap inside (where the wire connects with the terminal). I assume that this caused the fuse to blow when something shorted out - however, I thought that glass is an insulator and not a conductor so I have no idea how that would have happened.
I went to Maplins and came home with some F630mA fuses - different to what I took out which was T630mA. I am assuming F stands for Flink (German for "speedily" or presumably quick) and is therefore a quick blow fuse - T presumably is a time-delay blow and offers some extra protection. I replaced the fuse, which promptly blew again, so I don't know what's wrong with it now and I've got gigs coming up!! Bloody thing.

Any ideas what's gone wrong? When whatever shorted out, could it have knackered it up totally?

edit - there is a pic of a terminal block in there, but I can't see it - if you can't it's just a plastic terminal block which was used to connect the speaker cable together. I don't know why, but the first mod is to sack that off for a straight cable.

Edited August 18, 2008 by john_the_bass

[escholl]

could be a few things. most amps have a bit of an input current surge when they first turn on, to putting in a time delay fuse would be a step in the right direction.


however...if that fuse blew in the first place it could be something else more serious. the lights should still come on however, so the first step is definitely putting the right fuse in and seeing what happens.

most tube amps are pretty robust, more so than their SS equivalents, so it's no doubt fixable. keep us updated.

[john_the_bass]

Problem solved - as I thought, the reason it was blowing fuses was because I was fitting it with the wrong fuses - the quick blow or F fuses.
I put a T (Time delay) fuse in, as I should have done in the first instance and it's working fine.

All good and I'm very happy and relieved. I shall be buying the bloody thing a set of covers, some new output valves and a new speaker now!

[escholl]

[quote name='john_the_bass' post='264882' date='Aug 18 2008, 08:09 PM']Problem solved - as I thought, the reason it was blowing fuses was because I was fitting it with the wrong fuses - the quick blow or F fuses.
I put a T (Time delay) fuse in, as I should have done in the first instance and it's working fine.

All good and I'm very happy and relieved. I shall be buying the bloody thing a set of covers, some new output valves and a new speaker now![/quote]


you probably don't need new valves/speaker, unless of course you just want to

[john_the_bass]

Oh no - it doesn't [i]need[/i] new valves an a speaker, it's just got a set of crappy Sovteks for the output and an HH Invader speaker - they both need swapping for something a bit better and the covers will stop anymore of the tolex getting whacked off!

[Zerofret]

Unless you've got a specific problem or fault, there is nothing wrong with Sovtek valves! - they are rebadged and fitted by most of the top amp makers. A lot of valve specialists including Groove Tubes use them for some of their valves. They are well made and stand up to some fair old hammer. If you don't mind a slightly cleaner sound their EL84M (M for military) is a cracking valve, able to stand up to more punishment than a regular EL84.

Cheers
Steve


[quote name='john_the_bass' post='265242' date='Aug 19 2008, 09:26 AM']Oh no - it doesn't [i]need[/i] new valves an a speaker, it's just got a set of crappy Sovteks for the output and an HH Invader speaker - they both need swapping for something a bit better and the covers will stop anymore of the tolex getting whacked off![/quote]

[john_the_bass]

Cheers Steve. The Sovteks in mine were at least 4 years old, probably had a bit of life in them, but I'd read good things about the JJ's (I have a set of JJ's in the preamp after I whacked one of the old ones and broke it) and £39 didn't seem like a lot.

Revalved it yesterday and fitted a G12H and the difference, even at "not annoying the neighbours" front room level is noticeable. The clean channel seems cleaner and thicker sounding and the drive settings are amazing - you can still pick out all of the notes in a chord with the amp breaking up. Difficult to describe but I am very happy!