Another blowing fuse thread. Any help very welcome!

[Rslice97]

Im somewhat embarrased but while I was conducting the voltage tests I seemed to have shorted the power transformer terminal 1 with ground. There was a quick pop and the fuse blew. Up to that point everything was going well. Resistance and voltages were spot on. I replaced the fuse and when I turn on power it blows again. If someone could steer me in the right direction as to what I may have fried I would greatly appreciate it!
Thanks
Richard

 

[Grainger49]

Reading the manual, page 36/40 it says that transformer T1 is the incoming 120V.  Shorting that to ground would blow the fuse but not harm the downstream circuit.  And that is all the circitry and the whole transformer. 

But... it might smoke the wiring in the power cord.  Just use your meter to verify continuity between the IEC cord prongs and the female end.  Then verify that none of those are shorted together. 

Are you sure that transformer T1 got shorted to ground? 

Don't feel bad, I have let the smoke out of a lot of equipment and I have been building kits since the 60s.  I have meter leads with notches on the tips to prove it.

 

[Rslice97]

Hello and thank you for your reply! I checked the power cord and it is ok. I double checked the wiring to the power switch and to the power transformer in case I fried that and It seemed ok. I am pretty ignorant to the workings of the power transformer but while checking continuity I get continuity between the 1 and 2 posts on the transformer is that normal? Im not 100% that the #1 power transformer pin was shorted to ground but I know when I was testing that pins voltage. Again sorry for my ignorance but thank you for your help!

 

[Grainger49]

There is a winding between transformer T1 and T2, that's a wire.  So you will get continuity.

First check by touching your meter leads together, that is considered zero.  Then try between T1 and T2.  I bet it is higher.  That is the resistance of your transformer primary winding. 

So, you are still blowing fuses.  Hmmmm.... If you shorted what you said you did it should have only blown the fuse and left everything downstream, all that important stuff, alone.

I guess I'm stumped.  And I will be proven wrong. 

 

[Rslice97]

Well Ill check for anything shorted that shouldnt be again go get some more fuses and report back. At least I have some direction now so thank you!

 

[JC]

Pick up some 1A "Slow-Blow" fuses when you go out.  IIRC, these solved the fuse-blowing issue for some folks, when the fast-blow's wouldn't hold at start-up.

Then, a run through the resistance checks again should tell you if something else happened.  Though, as Grainger pointed out, grounding terminal 1 of the power transformer should have only resulted in the blown fuse.

 

[Rslice97]

Hey all just wanted to report first that the amp is working! Working very well!!! I cant pinpoint just what fixed the problem as I did a few things before firing it up this last time. For good measure I resoldered some joints, changed out the power cord, swapped tubes to some nos philcos and picked up some slow blow fuses and one of those things did the trick. No humm just music and life is good Im not betting on the cord but either the new fuses or maybe i had a piece of clipped lead shorting out somewhere but in any event I really appreciate all the help! I am also in the process of building some new speakers but im not really feeling the need at this point with the amp in the system!! THANKS!

 

[JC]

Good for you; enjoy!