Hi All
I recently got an output transformer for a 100w Marshall superlead I am going to build soon. While handling the transformer ( I was removing the covers to replace the bolts) I realised there is a scratch across some of the laminations on the side of the transformer. I don't remember if it came like that or if it's my fault. I assume it is my fault though.
As you can see from the picture the scratch is interrupted where the laminations are lower. I tested for continuity and indeed where the scratch is continuous i get some of the laminations shorting.
Is this a significant damage? Is this going to affect the performance of the transformer in a negative way? What about the sound?
Is it a good idea to dab some insulating varnish on the scratch? Although I know that if there are burrs bent across the laminations the varnish will not fix it. What do you think?
Consider that I will play the amp at high volumes using a dummy load most of the time so the OT will get saturated. But as far as I know it doesn't overheat like a PT would.
Thanks
I recently got an output transformer for a 100w Marshall superlead I am going to build soon. While handling the transformer ( I was removing the covers to replace the bolts) I realised there is a scratch across some of the laminations on the side of the transformer. I don't remember if it came like that or if it's my fault. I assume it is my fault though.
As you can see from the picture the scratch is interrupted where the laminations are lower. I tested for continuity and indeed where the scratch is continuous i get some of the laminations shorting.
Is this a significant damage? Is this going to affect the performance of the transformer in a negative way? What about the sound?
Is it a good idea to dab some insulating varnish on the scratch? Although I know that if there are burrs bent across the laminations the varnish will not fix it. What do you think?
Consider that I will play the amp at high volumes using a dummy load most of the time so the OT will get saturated. But as far as I know it doesn't overheat like a PT would.
Thanks
Drive 6.3V 50/60Hz AC through a 10 Ohm resistor to the 8 Ohm winding. Measure the ACV on the 8 Ohm side. Do NOT get fingers on the plate-side leads! (They will be hundreds of Volts.)
A healthy transformer (that size) will show well over 4.0V, probably >5.0V. The unloaded impedance is higher than the nominal impedance.
A badly-scratched transformer might show under 2V. The inter-lam shorts form little loops conducting through steel. Even though it is high-R steel, they tend to short-out all windings.
Some more careful frequency sweeps (need a low-impedance source, not a line level) might tell more.
_I_ suspect that scratch is "not bad". But I could be wrong.
A healthy transformer (that size) will show well over 4.0V, probably >5.0V. The unloaded impedance is higher than the nominal impedance.
A badly-scratched transformer might show under 2V. The inter-lam shorts form little loops conducting through steel. Even though it is high-R steel, they tend to short-out all windings.
Some more careful frequency sweeps (need a low-impedance source, not a line level) might tell more.
_I_ suspect that scratch is "not bad". But I could be wrong.
Drop some thin CA glue on the scratch. The stuff wicks in pretty good and might give some areas a little more insulation. In my opinion (for what it is worth) it is not all that bad, just don't do it again.
Let me get this right. I have a 6.3v filament transformer here. Without load it puts out 6.7vac.
I've put some power resistors in parallel to get about 10.9 ohms.
I hooked one side of the multimeter and one side of the 6.7vac on the OT secondary common.
Then I hooked the other side of the 6.7vac to one side of the 10.9ohm resistor.
Then I hooked the other side of the resistor to the 8ohm tap of the OT and the other side of the multimeter.
I measure about 6.5vac. I get very little voltage drop. Is this correct?
Thanks
Last edited:
> I measure about 6.5vac. I get very little voltage drop. Is this correct?
I think the transformer is excellent.
I think the transformer is excellent.
i have grinded loose an EI traffo that was welded, cleaned off the welds so that lams came loose or separated easily, then when done on the windings put those back interleaved rather than weld them back, and the traffo worked like new....
that was a 230 volt conversion on a 100 volt japanese unit...no problem after that...
that scratch on your traffo is a mere annoyance, a typical newbie reaction, nothing to worry about really... 😀
that was a 230 volt conversion on a 100 volt japanese unit...no problem after that...
that scratch on your traffo is a mere annoyance, a typical newbie reaction, nothing to worry about really... 😀
- Status
- Not open for further replies.