Preparing to rewind an OPT from a Lux amp, the OPT is a model OY15-5 15W 5K, in general Lux OPT's seem to be highly regarded, so will be interesting to see what sort of magic is in the windings/layout.
A bit of background:- A local amp builder for whom I wind transformers handed me a home made bobbin which looked to suit a 50mm stack of EI76 laminations, the instructions were for me to calculate turns and wire size using his winding layout, once he was ok with the design then to go ahead and complete the winding, a few text messages later I find out the resulting transformer is to replace a failed Lux OY15-5 OPT, an attempt had been made by a 3rd person (unknown) to unwind the transformer and document the winding layout, turns etc for later rewinding, the 3rd person had given up saying too hard, so it was decided to wind a new transformer using the old laminations, which is where I entered the picture.
I believe that model transformer was common to a few different Luxman amps - Luxman amps have a good reputation and and bring good money so I figured it was well worth the effort the rewind the transformer correctly, he gave me the damaged windings to see if I could do any better unwinding the transformer, document the winding layout and then rewind. While I don't have the original laminations at this point, an EI76 lamination fits the bobbin - 25.4mm central leg - so I assumed this was the correct size.
The OY15-5 transformer is potted in pitch and luckily (for me) someone had already done this part, and removed the transformer proper from its enclosure and also melted off most of the pitch, they had also removed some of the windings. On examination, it looked to me that there were 3 secondary windings all connected in parallel and possibly 4 primary windings with ultralinear taps. As given to me a primary winding was exposed - inserting an EI76 lamination showed a fair amount of room between the winding and the lamination, this supports the story that one or more windings - primary or secondary - had already been taken off, working on the assumption that the last winding would have been a primary I guessed that a primary and secondary winding had already been removed, if this was correct then primary windings would 5 with 4 secondary windings
On to the unwinding - the winding (primary) came off easily I noted that no special precautions had been taken to anchor the last turn, just 1 narrow strip of mylar tape the hold it. The primary layers were separated by a layer of thin plastic like insulation definately not paper - possibly mylar or maybe even nylon around 0.04 - .05mm thick, it feels more like nylon to me.
Next came 1 layer of transformer paper insulation 0.15mm thick covering the secondary winding which consisted of 2 layers, 1 full layer and a second layer with various taps to cater for different speaker loads. Under this was another layer of transformer paper to separate the secondary from the primary layer underneath - it is here I've hit an first obstacle
this primary winding is completely fused together with the thin interlayer plastic insulation - some sort of massive overload has heated it to the point where the plastic insulation has melted and fused to the wire, it's going to need some extra care to unwind so I can count the turns, tried to carefully unwind but the thin 0.19 primary wire breaks easily, I'll need to find a way to soften the fused mass so I can unwind.
So looks like I'm going to need some patience here getting the wire off this winding isn't going to that easy.
A bit of background:- A local amp builder for whom I wind transformers handed me a home made bobbin which looked to suit a 50mm stack of EI76 laminations, the instructions were for me to calculate turns and wire size using his winding layout, once he was ok with the design then to go ahead and complete the winding, a few text messages later I find out the resulting transformer is to replace a failed Lux OY15-5 OPT, an attempt had been made by a 3rd person (unknown) to unwind the transformer and document the winding layout, turns etc for later rewinding, the 3rd person had given up saying too hard, so it was decided to wind a new transformer using the old laminations, which is where I entered the picture.
I believe that model transformer was common to a few different Luxman amps - Luxman amps have a good reputation and and bring good money so I figured it was well worth the effort the rewind the transformer correctly, he gave me the damaged windings to see if I could do any better unwinding the transformer, document the winding layout and then rewind. While I don't have the original laminations at this point, an EI76 lamination fits the bobbin - 25.4mm central leg - so I assumed this was the correct size.
The OY15-5 transformer is potted in pitch and luckily (for me) someone had already done this part, and removed the transformer proper from its enclosure and also melted off most of the pitch, they had also removed some of the windings. On examination, it looked to me that there were 3 secondary windings all connected in parallel and possibly 4 primary windings with ultralinear taps. As given to me a primary winding was exposed - inserting an EI76 lamination showed a fair amount of room between the winding and the lamination, this supports the story that one or more windings - primary or secondary - had already been taken off, working on the assumption that the last winding would have been a primary I guessed that a primary and secondary winding had already been removed, if this was correct then primary windings would 5 with 4 secondary windings
On to the unwinding - the winding (primary) came off easily I noted that no special precautions had been taken to anchor the last turn, just 1 narrow strip of mylar tape the hold it. The primary layers were separated by a layer of thin plastic like insulation definately not paper - possibly mylar or maybe even nylon around 0.04 - .05mm thick, it feels more like nylon to me.
Next came 1 layer of transformer paper insulation 0.15mm thick covering the secondary winding which consisted of 2 layers, 1 full layer and a second layer with various taps to cater for different speaker loads. Under this was another layer of transformer paper to separate the secondary from the primary layer underneath - it is here I've hit an first obstacle
this primary winding is completely fused together with the thin interlayer plastic insulation - some sort of massive overload has heated it to the point where the plastic insulation has melted and fused to the wire, it's going to need some extra care to unwind so I can count the turns, tried to carefully unwind but the thin 0.19 primary wire breaks easily, I'll need to find a way to soften the fused mass so I can unwind.
So looks like I'm going to need some patience here getting the wire off this winding isn't going to that easy.
