Power transformer smoking!

lepeu66 · Post by **lepeu66** » Sat Oct 13, 2007 7:04 pm

Ok....heres what i have done. I replaced some of the cf resistors on my JTM45 board with NOS CC. All was well until I fired her up for biasing and testing. Did so and blue fireworks from rectifier, red plating, then fuse blown. Ok, checked for accidental grounding mess ups and such. couldnt find a thing. I then removed all tubes and started testing voltages. Severely high voltages on pins 4 and 6 on rectifier. then smoke from PT. I am assuming it has shorted out. Any ideas...Anyone?

lepeu66 · Post by **lepeu66** » Sat Oct 13, 2007 7:21 pm

Also, should The connections on the white wire from the rectifier and the bdard be referenced to ground?

neikeel · Post by **neikeel** » Wed Oct 17, 2007 6:35 am

I think that you will need to post a couple of pics of what you have done (if you have a before and after that would be even better

)

lepeu66 · Post by **lepeu66** » Thu Oct 18, 2007 6:41 am

Before And After

lepeu66 · Post by **lepeu66** » Thu Oct 18, 2007 8:40 am

Also I removed all secondary connections and fired er' up....smoke followed, so it is definetly shorted or somthing.

bluze81 · Post by **bluze81** » Thu Oct 18, 2007 9:28 am

You must have hooked up your primary leads wrong,have you gone back thru to make shure all contacts are correct? its hard to tell by the pictures.

neikeel · Post by **neikeel** » Thu Oct 18, 2007 11:17 am

If all you did was replace the input resistors, the mixers and V1 plate resistors you would not have needed to rebias and you would not have been able to create any PT mischief.

Did you do anything else to teh amp at the same time, left some swarf or solder around the place, replaced tubes etc.

Your mains fuse should have gone to protect things first if wired correctly, the HT fuse protects the system downstream of where your problem appears to be. I agree with Bluze I cannot make much out from the pics you have posted.

Could you do some close ups of the PT, filter cap and switch arrangement.

Either way a smoking PT is bad news, as I said if your fuse is the correct size and rating the mains fuse should pop.

lepeu66 · Post by **lepeu66** » Thu Oct 18, 2007 11:17 am

Primary leads were fine for about 8 months, so that isn't likely it.

lepeu66 · Post by **lepeu66** » Thu Oct 18, 2007 11:38 am

Here a closer look at the power. I swear all I did was change some resistors and rotate some of the coupling caps so foil end sits towards tubes. , ohh, and did replace the diode, I have checked that and it checks out perfectly with a DMM. I checked to make sure nothing is grounded that shouldn't be. I've kinda narrowed it down to either a bad rectifier, or there was somthing inherently wrong with the transformer from the get go, just picked a long time to show its dark side. I did have the wrong mains fuse in (4amp), so that why it didnt' blow. I'm just dumbfounded.

bluze81 · Post by **bluze81** » Thu Oct 18, 2007 6:11 pm

So this build did work fine for 8 months? also what size fuse is in the holder mounted next to the tranny? and its not popping the fuses at all when powering up?

lepeu66 · Post by **lepeu66** » Thu Oct 18, 2007 6:59 pm

That was the correct 500ma fuse. It did bust some fused right out of the gate...but that evened out. Yep, she sounded like angels since the beginning. I tested the rectifier tube, It is now shorted, but that could have happened during the fireworks a few days ago. So I have to say the issue is indeed the tranny. but I wont know that until i get a new one.

lepeu66 · Post by **lepeu66** » Sat Oct 20, 2007 10:23 am

OK....I'll admit it....I'm a moron....Seems the new diode was installed backwards....stupid me for not testing and trusting some pictures. Now, my question is, could this have caused the pt to overload?

neikeel · Post by **neikeel** » Thu Oct 25, 2007 4:24 pm

Yup 'specially with wrong fuse

lepeu66 · Post by **lepeu66** » Sun Nov 11, 2007 9:33 pm

Answer: I installed the new PT, seems wrong diode orientation and wrong fuse is equal to $125 ERROR. All is well now