Output Transformer Damage???

[GregS]

I was doing the last soldering connections of my first build and would have been ready to start testing it had I not damaged a part from too much heat. I was using a 45 Watt Weller iron instead of the 25 Watt one I'd used for almost all of the build as I was soldering to the lugs of a switch and thought I could use a little more heat. This was my speaker impedance selector switch which I soldered my OT secondaries to as well as a 250 Ohm 5 Watt power resistor. I got the connection(s) way too hot as the solder was still liquid and bubbling about 5 seconds after I removed the iron. I destroyed the power resistor despite having an alligator clip on the lead as a heat sink. It only reads 20 Ohms now. I also destroyed the switch (heavy duty switch) as it is all shorted out internally now. Sounds really stupid but I didn't think a 45 Watt iron would get things that hot for the amount of time I had it on the connection.

Kind of a pain that I have to order another resistor and wait for that before trying it out as I don't have a spare. My greater concern though is if there's a possibility I damaged my OT from this extreme heat. The transformer leads are roughly 7 inches long 18 guage wire. Does this sound possible or likely? Is there a way I can test it such as applying a known voltage to one of the secondaries and measuring the voltage on the primary? The transformer is a Hammond 1650F.

Thanks,

Greg

[tubeswell]

One quick and dirty way of checking is to put your ohmmeter across the primary and secondary winding(s) to see if you've got continuity where you should have and that you haven't got continuity where you shouldn't have.

[Enzo]

Remember, the transformer winding has a low resistance and now your switch and resistor are all wired to it, so unless you unwire the resistor to remeasure it, I'd be it is fine. It is extremely unlikely that solder heat turned a 250 ohm power resistor into a 20 ohm one. Heat usually makes resistors go higher in resistance. And if it is a wire wound - as I suspect it might be - even more unlikely. And while you COULD have melted the switch, I suspect the "all shorted out" inside is really just the resistance of the transformer winding. The secondary - the side that connect to the speakers - of most guitar amp output transformers is less than an ohm in resistance.

[black_labb]

i also doubt you burnt out a 5w resistor. the reason the solder probably stayed molten longer would partially be because of alot of metal holding the heat. heavy duty components have more metal there which make the temperature slow to heat and slow to cool.

how often does someone burn out a 1/2 watt resistor? your resistor has 10 times the resilience to burning out than a 1/2 watt one.

[GregS]

Thanks for the replies.

Remember, the transformer winding has a low resistance and now your switch and resistor are all wired to it, so unless you unwire the resistor to remeasure it, I'd be it is fine.

I think this is the case. It occurred to me some time after the fact that there would be alternate paths for current to flow with the OT secondaries connected. Also the fact that I have a 20 Ohm resistor adjacent to the 250 Ohm and I'm getting a 20 Ohm reading accross the 250 seems a lot to be coincidence. I think the current from the meter is flowing through the transformer winding to ground and then through the 20 Ohm resistor to my other meter test lead. I'll measure it out of the circuit tonight and confirm this.

Thanks again,

Greg

[GregS]

Good news! Nothing damaged. Resistor measured 250 Ohms again out of circuit. Switch is fine. On to testing.

Greg