Hi
I recently built an amp with a Tube Town "Trainwreck Express" power transformer which I now seem to have some trouble with. It worked fine for a few hours but then it started to blow fuses (mainly my houses fuse). After tinkering a bit I desoldered the secondaries and did some measurements. This transformer should normally give about 300-0-300V. Measuring between the outer sides it gives about 643V and between either side and CT it gives about 320V, which is about correct with the voltage at 238V in my wall today fed into the 230V input of the transformer. However, when I measure relative to ground I get 236V on one side and 877V on the other side. CT is measuring 553V volts to ground, so no wonder why my fuse keeps popping when attaching the CT to ground. The heater secondaries measures fine.
Am i correct suspecting that there is something fishy going on inside this transformer? Is there other measurements I should have tried?
goldenGeek wrote: ↑Wed Mar 23, 2022 10:08 am
However, when I measure relative to ground I get 236V on one side and 877V on the other side. CT is measuring 553V volts to ground...
Please describe exactly what you are doing to get these readings. This doesn't make sense. If you get reasonable and symmetrical readings with the leads floating, as described about 320-0-320, then this seems impossible. Are the leads floating when you do this? Are you putting one meter probe on the chassis and the other probe on one lead at a time?
Phil_S wrote: ↑Wed Mar 23, 2022 12:43 pm
Please describe exactly what you are doing to get these readings. This doesn't make sense. If you get reasonable and symmetrical readings with the leads floating, as described about 320-0-320, then this seems impossible. Are the leads floating when you do this? Are you putting one meter probe on the chassis and the other probe on one lead at a time?
If I stick the CT to ground (chassis) the fuse in my house pops out, so the readings was with all secondaries disconnected/floating. The "weird" readings was between the floating secondary (one at the time) wires and chassis.
goldenGeek wrote: ↑Wed Mar 23, 2022 10:08 am
Hi
I recently built an amp with a Tube Town "Trainwreck Express" power transformer which I now seem to have some trouble with. It worked fine for a few hours but then it started to blow fuses (mainly my houses fuse). After tinkering a bit I desoldered the secondaries and did some measurements. This transformer should normally give about 300-0-300V. Measuring between the outer sides it gives about 643V and between either side and CT it gives about 320V, which is about correct with the voltage at 238V in my wall today fed into the 230V input of the transformer. However, when I measure relative to ground I get 236V on one side and 877V on the other side. CT is measuring 553V volts to ground, so no wonder why my fuse keeps popping when attaching the CT to ground. The heater secondaries measures fine.
Am i correct suspecting that there is something fishy going on inside this transformer? Is there other measurements I should have tried?
wpaulvogel wrote: ↑Thu Mar 24, 2022 1:37 am
Sounds like your chassis is at 238 volts
Wish I'd thought of this! 877-238 = 639. That is right in line with 320-0-320. I think it is time to show pictures of the build. Let's see all of the transformer wiring, including the mains wiring coming into the chassis, the mains ground (if there is one -- not familiar with Euro standards,) the mains fuse, the secondary connections, and anything else. Make sure to show the 50V bias tap that Stevem is talking about.
goldenGeek wrote: ↑Wed Mar 23, 2022 8:45 pm
I measured between primary and secondary windings and there is alomst 0R between two of the wires.. I guess the insulation is gone
if this is correct , transformer is useless, and you can start to write complain to tube town unfortunatelly
It all make sense, there is no floating 230V on the chassis, but when the primary is shorted to the secondary at the end of each coil the voltages and everything makes sense. Thanks for the help I made an inquiry with customer support and it seems like they will be really cool about this I can post a picture, but there is a crazy mess since I have desoldered the whole secondary side..
goldenGeek wrote: ↑Fri Mar 25, 2022 10:18 am
It all make sense, there is no floating 230V on the chassis, but when the primary is shorted to the secondary at the end of each coil the voltages and everything makes sense.
SoulFetish wrote: ↑Sat Mar 26, 2022 9:21 am
Umm.... What?
Like this…? I might have it all wrong, but the Numbers add up (I used the theoretical Numbers on the drawing, my measurements were a little higher).
997A90FF-AB4A-467D-B67A-A839FD8D23E3.jpeg
The reference/measurement to ground when the secondaries is floating and there is a short between primary-secondary has to do with the type of electrical system here. It’s 400V TN into my house which means that there is 230v between L and N, but you will also measure 230v between L and G, which is how this is supposed to be. When there is a short between the windings you will get readings from secondary to ground/chassis because of this.
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Stevem wrote: ↑Sat Mar 26, 2022 12:35 pm
Ok, so with a resistance test do you read a short or a low resistance between the primary and either leg of the 300/300?
This was answered on March 23. I think we can conclude there is a short and the transformer is toast. Bepone picked this up right away. He gets first prize!
on the other side. CT is measuring 553V volts to ground, so no wonder why my fuse keeps popping when attaching the CT to ground. The heater secondaries measures fine. 
I made an inquiry with customer support and it seems like they will be really cool about this