ugh! Hope I didnt burn up my PT....

[beasleybodyshop]

so.... setbacks on my Express build, I had everything wired up and flipped the switch - lights up, no tubes in. flip the standby switch, start checking voltages, then I realized I forgot to solder in the ground wire from pins 1/8 on the power tube sockets. So I wire those on, flip the switch...and it starts to smoke. so I quickly unplug it and find one of my heater wires and one of the CT wires are fused together at part of the insulation


I think this had something to do with wiring the ground lug, but Im at a loss. Any ideas guys? Day is officially ruined.

[M Fowler]

Your going to have to slowly go over every connection checking with schematic and layout to make sure everything is wired correctly.

Neatness is essential if the amp is going to work properly.

[romberg]

And use a lightbulb current limiter before you fire it up again (if you did not the first time . It is a good idea to pull all the tubes and bring it up with a limiter. Then put in the tubes and see if any draw too much current. It can (but not always) save some parts from going up in smoke.

Mike

[JazzGuitarGimp]

I would have thought the mains fuse would have popped pretty quickly with a shorted filament winding.

[sepulchre]

What, exactly, was smoking?

[beasleybodyshop]

What, exactly, was smoking?

PT was smoking. Ugh. CT and one of the heater wires fused together at a few points - Can I solder new leads for this? I think my PT might be ok - It didnt feel hot immediately after I pulled the power.

Gotta say, this has drained me mentally. I spent all night cleaning up my lead dress and right before I went to bed...poof.

[M Fowler]

I'm curious as to your wiring of the PT, center tap grounding, filament supply wiring etc.

[cbass]

https://tubeamparchive.com/viewtopic.php?t=20341

This is the first thing you need to do

[beasleybodyshop]

Ok, going to take a step back and re evaluate things.

Going to Home Depot today for parts for the current limiter.

Also going to make some new leads for the PT. I've carefully pulled away the aluminum and tape covering the terminal leads - looks like I can just resolver the new wires on.

[beasleybodyshop]

Ok so I checked the resistance on the primary and secondary sides. Primary side CT to 120v reads 2.3 Meg Ohm and the secondary CT to B+ is 24 ohms. Safe to say this trafo is bad?

[Firestorm]

Primary CT??

[JazzGuitarGimp]

There should not be a Center Tap in the primary winding. Now, if you are measuring from the secondary CT to the primary winding, you should see infinate resistance (2.3M is too low). If you were touching both meter leads while taking this measurement, the 2.3 M could have been your body resistance,

[RJ Guitars]

Thanks for posting this on the forum, it's like having 24/7 access to the best tech help you'll ever find. I'll provide a schematic of that transformer and maybe you can provide us some of your build photos. That should provide what is needed to sort out the issue of why it happened.


In the meantime I'll give you a few resistance measurements so you can compare with your results. I've labeled the terminals on the schematic to help clarify my measurements...

1-2 = 25 ohms - B+ lead to center tap
2-3 = 25 Ohms - B+ lead to center tap
1-3 = 50 ohms - B+ lead to B+ lead

4-5 = less than 1 ohm
5-6 = less than 1 ohm
4-6 = less than 1 ohm

7-8 = less than 1 ohm

If you get anything close to these values you should be O.K. I'll be curious what your results are.

thanks,
rj

[beasleybodyshop]

Well, I must be having a lucky day - all my measurements match up with what RJ has given me - So Im gonna guess that my transformer is ok. I hooked up the 120v leads to the L and Neutral lugs of a plug with both CT leads hooked up to earth. I rigged all this through my current limiter and it appears to be ok. Will post wiring photos tomorrow morning. Thanks for all the help guys!

[beasleybodyshop]

Here are some photos after I pulled the PT. I broke my panelmount fuse holder, so I installed one that was too big for the hole, so excuse the fuse and switch just laying there.

Also. i think i might have an issue with the way my VVR is wired. I have the B+ Out going to the positive lug of one of my 50uf cap cans. B+ IN is going to standby switch. Is this correct? I was just going off pictures I found here on TAG.