<div dir="ltr">If one winding is taking too much current due to a short, I expect the other (unshorted) winding would also draw excess current when energised, due to coupling through the core.<div>You could test this hypothesis by measuring the resistance of each of the primary windings.</div><div><br></div><div>paul perry melbourne australia</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Fri, Feb 20, 2026 at 2:14 PM grant <a href="http://musictechnologiesgroup.com">musictechnologiesgroup.com</a> <<a href="mailto:grant@musictechnologiesgroup.com">grant@musictechnologiesgroup.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u></u>
<div>
<div>I repaired a Garnet amp that blew its transformer when the generator it was hooked up to had been set for way too high a voltage (I don't remember what the customer said the voltage was, but they admitted the festival was smokier
than originally planned). I think that was all that was wrong too. Aside from fuses. <br>
<br>
GB<br>
<br>
On 2/19/2026 5:20 PM, Jean-Pierre Desrochers via Synth-diy wrote:<br>
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<div>
<p class="MsoNormal"><span lang="EN-CA">A customer brought me a guitar preamp that he said ‘blows its internal fuses..’<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">I checked the internals and found that both of the internal 315mA primary windings fuses were blown (F2 & F3).<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">The main 500mA fuse (F1) was ok.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">So I connected my variac to <u>only one</u> of the primary windings (no fuses) to find that<br>
reaching around 90VAC it started to drain around 1 AMP !<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">I checked the other primary winding alone and it behaved exactly the same,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">1AMP at around 90VAC.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">These measures were done with none of the secondaries connected (free wires).<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">So my questioning is what the heck almost shorted each of these primary windings<br>
exactly the same way..?<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">I connected external AC voltages to each of the secondaries bridge (one at the time)<br>
and there were no shorts on each of them. The resulting DC voltages were as expected.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">To create those shorts at each primaries it would have needed<br>
that the 315mA fuses would have been replaced by much higher values<br>
with some kind of shorts somewhere in the secondaries side.. ?<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">OR this is a manufacturing default that waited to awake ?<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">Anyway I ordered a new transformer replacement, but I don’t want<br>
to fry it again because of something else that blew the first one..<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA">What do you think ?<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-CA"><u></u> <u></u></span></p>
<p class="MsoNormal"><img width="802" height="301" style="width: 8.3541in; height: 3.1354in;" id="m_5644347112724503134Image_x0020_1"><u></u><u></u></p>
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