Odd normal vol channel..

[The Captain]

Yes 2 fuses: one in amp (2A sloblo "T2AL" in series before amp's AC switch as on the 5E3 layouts) the other in amp's mainsplug for the wall (3A will change to 1A if applicable to Uk). The limiter has one 13A in its mainsplug. We always have fuses in our plugs here without there'd be a hole in it- perhaps confusion lies here?

Im yet to check any voltage in amp- will do this ev: should I leave tubes in, and where exactly is best spot to place MM red probe (black on chassis obviously), assuming I am applying only amp's AC switch and not its standby?

Sorry for any confusion I may have flung about.. muchos, Captain.

[stokes]

"2A sloblo "T2AL" in series before amp's AC switch as on the 5E3 layouts".This is the one that should be 1amp,it is 2amp here.The other one I have never seen and is the cause of the confusion,not used in this country.
The first voltage check will be to make sure the limiter is working right,so you will check that you have voltage at the PT primary to wall connection.Put your meter on AC and check this.If there is voltage there then we know the limiter is okay.Now check if you have filament voltage,if you have and the pilot lamp is not lit then the pilot bulb is burnt out.

[The Captain]

something serious ain't right- I attatch MM set to AC with black on chassis and red just after amp fuse (in amp, in fuseholder as per 5E3 layouts) to check for voltage in amp. I plug 100w into limiter (Lhs socket in pic below) switched to on, unlit and ready. When I plug amp into limiter (Rhs in pic below- amp AC switch defo off too)... all house loses power/ tripped; I think Ive lost my sanity this is farcical! my limiter again: http://i102.photobucket.com/albums/m...Picture277.jpg

Middle pins joined.
Rhs pin to lead's Live (brown).
Lhs pin to lead's Neutral (blue/ red in pic at bttm).
Top pins joined and to lead's Earth.

Neither; rhs pin/ lhs pin/ joined central pins/ joined earth pins.. have any contact or continuity with one another. (Apart from obviously the joined pins to each other).

[stokes]

I dont see how it can cause the fuse to blow,but the MM leads should not be connected to ground to check AC volts,they should be connected to the 2 AC components i.e. each side of the PT primary leads.The limiter looks to be okay in the picture,but maybe there is something about the mains supply in the U.K I am not familiar with,maybe Steve can see something here that I dont see.

[The Captain]

Maybe not having MM leads right caused it? though Im completely at sea with fuse values now; Ive 3 plugs' fuses using the limiter & amps fuse which you say should be 1A now -although I was recommended 2A sloblo by MJWB for Uk and was working fine for the 2 weeks- let alone what on earth Im meant to have now in the amp's plug for the Uk).

Can any UK users tell me exactly what fuse values to use for the amp, and for its mainsplug?

Mr. Stokes can you clarify this: "connect to the 2 AC components i.e. each side of the PT primary leads" or exactly where do I put the 2 MM probes? I can't understand 'each side' bit, as the primaries to me are all on one side, the secondaries t'other and as I've always read amp voltages with black MM probe to chassis before-? thanks.

[stokes]

When measuring dc voltages the black gets connected to chassis or ground.When checking ac voltages the probes get connected to both ac components,for instance the PT has two primary leads,both black right?Black probe goes to one of the leads,red probe to the other.Another example,on your power tube you have ac heaters connected to pin 2 and pin 7.Put one probe on pin 2 and the other on pin 7.
As for the fuse value confusion,the fuse in the amp that you see in the schematic is listed as a 2amp.That is for USA mains supply which is 120v.In the U.K. you have 220v mains supply so the fuse value for the U.K. would be 1 amp.The one you describe in the "plug" that is common to the U.K. and doesnt exist in the USA can be 3amp,or 2amp,as long as it is rated higher than the 1 amp in the amp.By having a 2 amp where you should have a 1 amp allows twice the current to hit the amp before the fuse blows,even tho the PT wont fry on the spot, over a time the PT is getting twice the current than it is designed for due to a short or possibly just a leaky cap in the amp,after a while the heat from the excess current causes the PT to slowly burn till it shorts out.I suspect this is what happened to you,but we still dont know for sure that your PT is fried.So here is what I want you to do,disconnect the PT secondaries,that is the heater supply and the 2 high volt (red?) to the rectifier.Put a 1amp slo-blo in the amp itself,where you had the 2amp.Forget the current limiter for the moment,plug the amp in and turn it on,if the fuse doesnt blow turn the standby switch to on.If the fuse doesnt blow your PT is okay,but I suspect it will blow on the initial start up before the standby is switched,in which case the PT is shot and we will start again when you get the new PT.I have a feeling your PT's primary is shorted and that is why the house breaker blew.

[The Captain]

Ah yes of course measuring AC across things as on heaters for 1st time checks.. muppet! not sure if any difference, but my primaries are grey 240v joining AC switch and black '0' joining mains lead neutral. (*incidentally is a 1A sloblo still correct for 240v? 220v before you may have assumed ours to be). Id better not cock this up again.. so to 2x check:

Im disconnecting secondaries: 2 HV reds from PT to recto, (*2 yellows from PT to recto too?), 2 greens from PT to pilot lamp. Im installing a T1AL in amp, and a 3A in amp's mainsplug (into wall). Should I be sealing all the bare ends to be safe, or just keeping an eye they dont touch anything or each other? will try this later, captain.

[Steve Conner]

OK, to clarify things:

In the UK, every mains plug (the plug is what we call the part on the end of the line cord that fits into a wall outlet) has a fuse integrated into it. This is the mysterious extra fuse that has been puzzling you, Stokes. The fuses are a standard type that can be bought from any hardware store and come in 2A, 3A, 5A and 13A. 2A or 3A are most appropriate for guitar amps.

As for the fuse in the amp itself, 1A should be fine, 2A is a tad high for 240V, like Stokes has been saying. I've had a 1A fuse in my main guitar amp for years, and it's a 60 watt unit with 6550s. It only blew once, and that was when I dropped a screwdriver in the chassis while tweaking it and shorted the B+ to ground

If your lights all went out, well, you probably have a RCD (what the Americans call a GFI) in your house's fuse box, and you somehow allowed current to leak from live to earth and tripped it. When measuring on the mains side of the PT, you should put the black prod on neutral, not earth.

If you're going to disconnect the PT, yes, wrap the loose wires sticking out of it in insulating tape.

[stokes]

Wasnt sure if it was 220 or 240 over there but either way it should be 1amp.Same rule,double the voltage halve the amps.You dont have to remove the yellow 5v heaters to the rectifier if you pull the tube.In fact if you pull all the tubes it is not necessary to remove the green 6.3 leads either just take out the pilot bulb as well.This check is going to tell us if your PT is shorted.With all the leads disconnected the only thing you are plugging into the wall outlet is the PT,so if it blows,the PT is problematic.The only thing I can imagine would cause the limiter to act as you described where the 100watt glows full and the pilot light on the amp doesnt come on is the PT primary is shorted,so we will sacrifice a 1amp fuse and not use the current limiter for this.

[The Captain]

3rd check finally done Mr. Stokes as you said; PT 2ndary wires unhooked, 1A amp fuse, no tubes in.... 1A fuse blew immediately.

My last Q really then is whether this may have damaged any other part of the circuit ie, OT? And of course if there is much I can do to prevent this PT dying happening again, assuming a similar PT is on its way(?).. or is it just bad luck and Im peeing in the wind now with any other checks/ diagnosis/ assumptions I can make.

[stokes]

Okay,now we know for sure the PT is fried.I am inclined to think something in the amp caused the PT to go south,shorted or leaky filter caps are a prime suspect.Assuming the current limiter is working correctly,and you use the proper fuse value,1amp as opposed to the 2amp you had there,you wont fry the new PT while using the current limiter.My theory is that you had a short somewhere and using the 2amp fuse caused too much current to flow thru the PT without blowing the fuse and killed the PT.Since the pilot light didnt light with the limiter,I suspect you fried the PT's primary,this of course is only theory,since from where I sit,I cannot see everything in the amp.When the new PT arrives we will go thru some tests with the limiter,and track down the short.This is why the current limiter is such a valuable piece of test equipment,if you had made one back when you first wanted help firing the amp up,we would have found the short before any damage could be done,at least it only cost some time and headaches,and you arent paying for a new PT.There is always the possibility that it was just a bad PT to begin with.

[The Captain]

Im inclined to think it was just a bad PT rather than any other part of circuit or leaky cap- but as Im apprehensive about the new PT dying I'll re-read your info and get sorted for new start up checks with the limiter..

Q- assuming PT here asap, shall I connect it up as normal ie all 2ndaries? I wont fire it up yet of course. Thanks Capt.

[stokes]

Sure,it could have been a faulty PT to begin with,as I said my theories are just that,theories.Its kind of a hell of a time to ask,but you are sure you are using a PT for your 240v and not an American PT for 120v's,right?When you get the new one wire it up as normal and fire it up with no tubes in it first,then shut it down,install the rectifer and fire it up again,shut it down and install the power tubes and fire it up again.If the light doesnt burn bright on any of these steps,install the preamp tubes and fire it up again,If the 100watt bulb burns bright after any step described above,the short is related to that part of the circuit.If you are lucky it was just a bad PT to begin with,lets keep our fingers crossed.

[The Captain]

New PT wired up (240v primary), 1A fuse, limiter, 100w lamp for testing:

1. No tubes/ then all tubes with just AC applied= significantly dim 100w lamp (not FROM 'bright' or even half bright though).
2. All tubes, AC + standby(closed)= 'half' lit lamp, not dimming though..
3. AC + standby(closed) no preamp tubes= half lit lamp as above..
4. As above with both output tubes taken out (one by one)= still half lit lamp..
5. So then as above with just recto tube= significantly dim FROM half lit lamp on innitial powering..

No fuses went/ pilot light lit
Once powered down and checking filter caps after 10mins before poking about (for safe voltages check) I noticed all 3 filter caps still at ~200v - after 30 mins still at 100v.. maybe this tells a tale? (apart from bloody good job I checked!), but Im completely lost at sea on all bar 5. of these results, as I expected any dim lamp to 1st be bright.

[The Captain]

Just tested:

Recto + preamp tubes (no power tubes) AC & stdby closed= significantly dim 100w FROM half bright on powering up..

so Ive nailed it to the power tubes or related circuits? Im still not happy about the bulb not dimming from a nrmally bright 100w bulb (its as if it dims right down from say a ~20w bulb; as the 5e3 is ~20w too maybe correllated/ this IS correctly bright?). Any help much appreciated, Capt.