My Amp's gone bung.

Gassage

So, my Twinolux was on standby, and I switched on and it died.

I've checked the fuse plug- assume internal fuse will go first?

@ICBM? Anyone?

MattFGBI

Yeah, check the fuses.  

How old is it? Did you get it new?

Gassage

@MattFGBI

Yeah- bought off Gary Chapman @ PMT.

2013 MY EC Twinolux.

Could you link the schematic? Where are the internal fuses?

Thx.

richardhomer

Internal fuse is a much lower rating than the one in the mains plug typ - so it will blow first.

Over the years I've had a couple that have blown when seemingly no fault was present. They are subject to a lot of vibration, which no doubt weakens them over time.

Try replacing it (it MUST be the same rating) and power up again.

If it goes again, probably best to have someone take a look - though if you have spares, you might want to try swapping the output valves first and trying again - I have had a faulty output valve take a couple of fuses out too.

ICBM

At this point you probably don't want to see the pics of the one I worked on last year...

Minor internal fire and serious wiring damage caused by stupid design - filament fuse (unnecessary) but no HT fuse (which are a very good idea).

When a power valve shorted it didn't blow the mains fuse, until after the valve socket had vitrified and burned a substantial part of the wiring loom, and fried a couple of components on the board above.

Hopefully it isn't as bad as that - if the fuse blew immediately, it shouldn't be. Still almost certainly a power valve failure though.

randomhandclaps

Maybe it's finally succumbed to Hiwatt envy!

randomhandclaps

ICBM said:

At this point you probably don't want to see the pics of the one I worked on last year...

Minor internal fire and serious wiring damage caused by stupid design - filament fuse (unnecessary) but no HT fuse (which are a very good idea).

When a power valve shorted it didn't blow the mains fuse, until after the valve socket had vitrified and burned a substantial part of the wiring loom, and fried a couple of components on the board above.

Hopefully it isn't as bad as that - if the fuse blew immediately, it shouldn't be. Still almost certainly a power valve failure though.

Stay safe kids.

http://i1284.photobucket.com/albums/a579/imadray/Clapton_zpsb3df4746.jpg

.

DannyP

In the white roooooom.....

thisisguitar

Mate, I hope it's nothing serious. Maybe Eric had some sort of counter built in… you played too much Gilmour without breaking things up with Sunshine Of Your Love ;-)

Gassage

Fixed. I had to change a whole fuse by myself.

Strat_a_tat_tat

Gassage said:

Fixed. I had to change a whole fuse by myself.

... and without the aid of a safety net.

meltedbuzzbox

Gassage said:

Fixed. I had to change a whole fuse by myself.

at least it was a nice cheap fix eh?

I thought you were going to sell that amp?

Bogwhoppit

Gassage said:

 Anyone?

Try Andertons

Gassage

No keeping for the time being. I have been cranking it at 10 on the 10w setting which is loverly.

thisisguitar

Good stuff. My old 5150 combo used to chew up a fuse now and again, always gives you a scare though.

@ICBM is it worth running amps like this through an RCD? Would it offer any protection to the insides?

ICBM

thisisguitar said:

Good stuff. My old 5150 combo used to chew up a fuse now and again, always gives you a scare though.

@ICBM is it worth running amps like this through an RCD? Would it offer any protection to the insides?

No. An RCD only protects against current leaking out of the amp.

These amps keep all the current inside, it's the smoke they let out .

http://www.theangelconversations.com/pics/Twinolux2.jpg

(Feel safe posting this now that I know Gassage's amp doesn't look like it inside! )

Sassafras

Jeez! Didn't realize valves could get that hot. Looks like someones taken a blowtorch to it.

ICBM

Sassafras said:

Jeez! Didn't realize valves could get that hot. Looks like someones taken a blowtorch to it.

It wasn't the valve that got that hot.

What happened was that the valve developed a short in the base, which produced soot which got onto the valve socket, and even though it was a ceramic socket this was enough to cause a continuous arc across between the plate connection (the blue wire I have already cut the damaged end off in that pic) and the filament connection (the slightly out of focus green wire which is melted), which got so hot it vitrified the socket and oxidised the chrome plating on the chassis.

http://www.theangelconversations.com/pics/Twinolux4.jpg

You can just seen the shiny grey spot where the ceramic and metal have melted into each other in the lower centre (sorry, not very in focus either!).

The heat generated also burned most of the wiring loom above the socket, which is why I simply cut it away - the only reason I didn't with the green wire was that I needed enough length to reconnect it, and it was already quite short.

The resistors on the board above (which are the 'virtual centre tap' for the filament) also burned out due to the plate to filament short.

*Finally* - at about the time the owner noticed loud cracking and smoke coming from his amp - it drew enough current to blow the mains fuse. Not the one on the board above, that's the filament fuse and did not blow.

An HT fuse would have blown at the *initial* valve short. It would have prevented all this damage.

So when I rebuilt the amp, I removed the filament fuse (they're not necessary really - certainly far less so than HT fuses) and rewired the holder as an HT fuse so this won't happen again. Fender please take note! All valve amps should have HT fuses - for some reason it's not standard practice for American amps, although it usually is for European ones.

Sassafras

Are they not fitted to US amps because of their lower voltage or is there some other reason?

Certainly wouldn't want this happening to any amp of mine!

hywelg

thisisguitar said:

Mate, I hope it's nothing serious. Maybe Eric had some sort of counter built in… you played too much Gilmour without breaking things up with Sunshine Of Your Love ;-)

More likely he played the first three chords of Sunshine and the amp said 'I ain't havin none of this raucousnuss, Tears In Heaven  gentle noodling is more my thing'

ICBM

Sassafras said:

Are they not fitted to US amps because of their lower voltage or is there some other reason?

Certainly wouldn't want this happening to any amp of mine!

Nothing to do with the supply voltage, once it goes through the amp's power transformer it's all the same. The HT fusing is on the secondary side.

The reason all European amps now have full secondary fusing (sometimes even excessively so) is down to EU regulations. But this isn't the reason older ones do, since the regulations didn't apply then - it can only be because the people who designed them were properly trained and experienced electronics engineers who knew that HT fusing was a good idea to prevent damage like that.

Why the Americans generally didn't, I don't know - the only reason I can think of is to save the cost of the fuseholder, since there is no other disadvantage of one. I'm actually surprised that US amps currently sold in the EU do not appear to have to comply with the regulations either!