Short in amp: house circuit breaker pops, amp fuse does not.

[Don Moose]

Since it did used to work, we can't take the path saying the PT was in ... um, sideways.

It sounds like the primary broke in a way that shorted it to the secondary.
(you already figures that out)

That PT is toast.

There are a couple of ways that could happen ... I think. High temperatures come to mind, but don't seem very likely. A voltage spike big enough to break down the insulation _and_ make an open doesn't sound very likely either.

How about 10 posts of wild speculation while Carlo orders a replacement?

[Steve Conner]

Wild speculation... The transformer wires got mixed up during the rebuild? Remember that transformer wire colours were only standardized in America.

[slidincharlie (Carlo P)]

Wild speculation... The transformer wires got mixed up during the rebuild? Remember that transformer wire colours were only standardized in America.

I don't think so... the amp has worked quite fine for about 2-3 years after PT rebuild.
Please help this dumb self-taught-tech-wannabe understand:
since I have no tension on the secondaries when mains AC is applied to the primary, I wonder: where does all the current go?
Furthermore:
this PT was built ex-novo by a local manufacturer according to specs from the amp schematic. Is it possible that poor craftsmanship (or poor quality components) results in a transformer failure after 2-3 years of faithful job?

[52 Bill]

Please help this dumb self-taught-tech-wannabe understand:
since I have no tension on the secondaries when mains AC is applied to the primary, I wonder: where does all the current go?

There is no path for the current to flow, because the primary winding is open. The current is not going anywhere.

Furthermore:
this PT was built ex-novo by a local manufacturer according to specs from the amp schematic. Is it possible that poor craftsmanship (or poor quality components) results in a transformer failure after 2-3 years of faithful job?

Yes, anything is possible.

I have a question for you about the way the wiring was done. You stated that one of the primary wires was attached to ground? Please explain, as there should never be any ac wire directly connected to ground.

[slidincharlie (Carlo P)]

I have a question for you about the way the wiring was done. You stated that one of the primary wires was attached to ground? Please explain, as there should never be any ac wire directly connected to ground.

Bill you are right, my statement was misleading.
I measured continuity between one primary and chassis with the PT leads still connected - because actually there is continuity between that primary wire and the HT secondary (and their CT). Actually, contrary to what I stated, there is no continuity between the fuse holder lugs and ground. Sorry about that.
Now a replacement power tranny is the only way to go, or can the current PT be repaired?
EDIT: I'll talk to the guy who built this PT and ask if he can check and possibly rewind it

[Don Moose]

The tranny can be repaired, but I would want a complete rewind - primary and secondaries - since it sounds like insulation on both was less than adequate.

It should be OK for your transformer guy to re-use the laminations, and _maybe_ the bobbins (are there bobbins?), but all new wire - preferably with better insulation is a must.

I do wonder if the labor of disassembling old one would cost him more than a fresh-from-scratch unit (which would give you the comfort of knowing all the wire is new).

Hope this helps!

[Dave Curtis, dB AudioTech]

Or maybe this time the fuse blew before the house breaker...



Yes, I can see it on the picture - you did it right.
Cheers,
Albert

Well, kinda. The blue wire (neutral) should go directly to one side of the PT primary, and the brown wire should go through the fuse (backside first) and then to the switch. Although in Europe, they normally switch both the neutral and the hot with a 2 pole switch.

You don't want to fuse the neutral. If you switch it, the switch must also open the ungrounded conductor (hot).

[icefloe01]

Well, kinda. The blue wire (neutral) should go directly to one side of the PT primary, and the brown wire should go through the fuse (backside first) and then to the switch. Although in Europe, they normally switch both the neutral and the hot with a 2 pole switch.

You don't want to fuse the neutral. If you switch it, the switch must also open the ungrounded conductor (hot).

I agree with this and was going to post likewise until I looked at the schematic. I would not fuse the neutral either, but that's how the schematic is drawn: Live wire to switch to PT, PT to fuse to Neutral. It's just not what I'm used to seeing.

Eric.

[slidincharlie (Carlo P)]

Thank you Dave and Eric for addressing this issue. I did not know that I should fuse the hot wire instead of the neutral. Actually nobody cares about where the hot and the neutral go in Europe as far as I know, or if the hot is blue or brown. Well, maybe electricians care about it, but not common people who make their own small house works, like replacing an old plug and the like.
Don, I'll inquire for the costs of such job and post here my decision.

[slidincharlie (Carlo P)]

Oops! Blue and brown wires rule doesn't apply here!

Well, kinda. The blue wire (neutral) should go directly to one side of the PT primary, and the brown wire should go through the fuse (backside first) and then to the switch (...)

Dave, I have thought about it a little bit, and I can tell you that definitely this rule does not apply here in Italy, and possibly in most European countries. In fact I can insert a plug into a wall socket either way, so one wire (the blue for example) can be hot or neutral anytime, and there is no way to make sure that you are always fusing the hot wire.

[icefloe01]

Thank you Dave and Eric for addressing this issue. I did not know that I should fuse the hot wire instead of the neutral. Actually nobody cares about where the hot and the neutral go in Europe as far as I know, or if the hot is blue or brown. Well, maybe electricians care about it, but not common people who make their own small house works, like replacing an old plug and the like.
Don, I'll inquire for the costs of such job and post here my decision.

The difference between U.S. and European color codes below

The U.S. code for single phase (like a regular power cord) is typically:

Black = Live or "Hot" and goes to the narrow blade of a power plug.
White = Neutral or "Cold" and goes to the wide blade.
Green = Ground or Earth and goes to the long round pin of a three prong plug.

The European code is my experience has been:

Brown = Live or "Hot"
Blue = Neutral or "Cold"
Green w/ Yellow stripe = Ground or "Earth"

Personally, I think the European code makes more sense when you associate color with temperature.

One of the problems with swapping the neutral and hot leads in a piece of equipment is that everything that was originally tied to the neutral line is now hot all the time, even when the power switch is opened. Just something to be aware of.

Eric.

[slidincharlie (Carlo P)]

The difference between U.S. and European color codes below
The U.S. code for single phase (like a regular power cord) is typically:
Black = Live or "Hot" and goes to the narrow blade of a power plug.
White = Neutral or "Cold" and goes to the wide blade.
Green = Ground or Earth and goes to the long round pin of a three prong plug.

I see. Unfortunately in Italy (as well as in many other European countries) the holes in the sockets are exactly the same, as well as the plug pins, so there is no way to know which pole is hot and which is neutral...
Thanks for clarifying the subject anyway

[Albert Kreuzer]

The fact that you can insert the plug either way is the reason for the obligatory two-pole switch.
The blue/brown rule still applies in house wirings, where the blue (neutral) has to be on the left and the brown (hot) on the right side of the socket (well, at least in theory...)

Cheers,
Albert

[slidincharlie (Carlo P)]

The fact that you can insert the plug either way is the reason for the obligatory two-pole switch.
The blue/brown rule still applies in house wirings, where the blue (neutral) has to be on the left and the brown (hot) on the right side of the socket (well, at least in theory...)

Well, sockets here have three holes arranged vertically
Seriously... is there any trouble using an amp built on US specs like this one, with European (well, Italian actually) AC wiring? Please consider that, except maybe a few marginal cases, electrical circuits here always have ground wiring.

[Dave Curtis, dB AudioTech]

Dave, I have thought about it a little bit, and I can tell you that definitely this rule does not apply here in Italy, and possibly in most European countries. In fact I can insert a plug into a wall socket either way, so one wire (the blue for example) can be hot or neutral anytime, and there is no way to make sure that you are always fusing the hot wire.

Hence, the use of a 2-pole switch to open the neutral and the hot at the same time.