Smoke coming from Crack transformer plugging in for voltage test

[mightygrey]

Hey guys,

Thought I was just about done on my first build :-[  - I did my resistance check, had a few anomalies. After finding the culprits (couple of solders here and there) and getting all readings coming back the way I should, I put in my tubes, and switched on the power. The tubes began to light up, but pretty shortly (15-20sec) noticed an acrid smell accompanied by some smoke out of what I think is the transformer. The transformer tower was very hot to touch for some time after unplugging it.

See attached, is there anything that may be causing this?

 

[bob lennon]

Wow, I have the p10 transformer in my new s.e.x. 3.0 build. The instructions had intermediate voltage and heater glow tests, it seems that basic crack is a build-through before the resistance tests.

 

[mightygrey]

I had annearlier voltage /glow test as well - these worked just fine.

 

[Deluk]

As part of the build up to building my crack I saved a selection of build pictures from the gallery. Mine, 240v UK and all of these use a PT-3 transformer and the wiring with those is totally different but identical in all of the photos. Is the PT-10 a new type of transformer for the crack, perhaps one that can be wired for both 120 and 230/240v?

 

[vetmed]

2 things come to mind that could cause such symptoms. One is that you have windings in the power transformer connected out of phase. The other more likely is that you have a dead short to ground somewhere. Do not power this up until you have found your problem. I'm surprised you didn't blow a fuse in the process . Can't really offer any more advice since I am not familiar with this circuit. BTW there are a lot of solder blobs, wires that are not trimmed short enough and burn marks on wire insulation to suspect a ground fault Good luck!

 

[fullheadofnothing]

1) To the peanut gallery: yes, the PT-10 is a different transformer than the ones in early generations, and has a configurable primary for different incoming voltages.

2) Not using the wire colors as specified makes it unnecessarily difficult to diagnose your issues. Changing the routing of the wires further muddles the issue, and in some instances, may impair your amplifier.

3) Only providing  a single photograph from a single angle also adds to the confusion; your symptoms suggest that you may have points connected that shouldn't be. Finding that requires clear visual representations.

4) Where does the wire attached to terminal 13 on the power transformer go? It disappears under the resistor and doesn't seem to emerge. The powerswitch terminal it is supposed to be attached to is hidden by a capacitor, and the wire is not routed next to the screw, as shown in the manual.

5) Many of your wires are stripped back way too far. This is asking for trouble. Particularly concerning is the heater wire going to A5. It looks like it is in contact with the chassis. Even if it isn't, it certainly could be. Trim that wire and get the insulation closer to the terminal. Further concerns include the red wire at A7 (and at the other end of this wire at the potentiometer), the red wire at B5,

6) Numerous component leads and wires have been left very long. Again, this is a shorting hazard. Wires and components should be trimmed close to the terminal after they have been secured. Terminals that appear to possibly be shorted to adjacent terminals in this photograph B2-B3, B8-B7, 20-21(capacitor lead to diode lead), A7-A8.

7) Virtually every one of your solder joints appears to have not been heated for a long enough time. When a joint gets hot enough to properly melt solder, it will form closely to the metal. It will not blob up. Note, for instance the solder on the legs of the 20U-21U capacitor. Once you have sorted all possible shorts, take the time to properly heat every solder joint in your amplifier.

 

[galyons]

1) To the peanut gallery: yes,

Seems a rather impolitic way to address your customers!?

Cheers,
Geary

 

[mightygrey]

Thanks for the advice guys. Think my first step is to get some better solder/iron. I can't get it hot to de-solder let alone melt the current 'blobs'. I was also petrified of running out of wire/not having enough to attach, so went a bit conservative there, and reused lengths of different coloured wire in a couple of places. Will report back after tidying everything up!

 

[troplin]

Thanks for the advice guys. Think my first step is to get some better solder/iron. I can't get it hot to de-solder let alone melt the current 'blobs'.

Often it helps to use a little bit of fresh solder to reflow existing solder joints. The fresh solder is providing some flux and acts as a "bridge" that helps conducting the heat to the existing joint.

Make sure that you heat the joint long enough until the solder is flowed completely. Most components in the BH kits are not particularly sensitive to heat. Just don't melt the power switch.

A better soldering iron (or even better, a soldering station) may certainly help, but you can also get decent results with a cheap iron.
The bigger the metal parts of the components, the more power you need. More solder needs also more power, so don't use too much solder.
I've built a S.E.X and the only parts where my soldering station (40W) came to its limits were the binding posts (the crack doesn't have those).

 

[Paul Birkeland]

If the wire lead that goes to A4/A5 touches the chassis, then you'll burn out your power transformer. You have stripped the wire back much, much further than advised in the manual, so I would take care of that immediately.

I also wonder about leads of the UF4007 diodes touching terminals that they are not connected to.  Did you pass the resistance checks?

 

[mightygrey]

Hi there,

Exposed wire definitely wasn't touching, but I shortened where relevant, and resoldered every joint on the amp. Passed my resistance checks with flying colours, but then got the same smell, crackling noise, and then smoke from the transformer again sadly.

Kinda at my wits end now in terms of what to do next - I could go ahead and de-solder every joint on the amp and start again (not the most fun prospect...), or is my transformer to blame?

Cheers,

Matty

 

[Paul Birkeland]

What resistance do you get at terminal 21?

 

[mightygrey]

So I went back and unsoldered pretty much everything on my Crack.

I did my initial AC voltage test - 248v was the result (I'm in Australia BTW).

I then did my secondary AC voltage tests.

Terminal 7/9 test = 4.5V

Terminal 11/12 test = 7.2V

The 7/9 result is lower than the 20% threshold, but the 11/12 test is significantly lower. Does this suggest a problem with the transformer?

 

[fullheadofnothing]

Your transformer has been irreparably damaged. Email replacementparts at bottlehead dot com to purchase a replacement.

 

[mightygrey]

Your transformer has been irreparably damaged. Email replacementparts at bottlehead dot com to purchase a replacement.

Thanks Joshua. Would you recommend I start again from scratch, or drop in the transformer and double check my work done to-date?

 

[Paul Birkeland]

I would personally remove all the UF4007's and the 220uF cap that goes with them, then start over.  That may require a new 6 lug terminal strip.

I still believe that there is a short wired into the amp on that terminal strip that has taken out the transformer, and putting a new transformer in is only likely to confirm my suspicion.

 

[Deluk]

A new transformer and associated parts may well be needed but I would consider returning the current, possibly u/s one, to Bottlehead. Yes it will be a moderate cost for postage Oz to USA, but would confirm the diagnosis.