Transformer winding with higher voltage than marketed

[bananasplit_00]

12V sounds pretty high for open circuit voltage, my 2.5A 220:6.3x2 transformer for my 8136 OTL amp was around 9.5V, but my line voltage is also 230V and not 220V.

I'd put a resistor in series(bolted to the case or a heatsink probably) like suggested by others unless you can get it swapped for a lower amps one. That's how I fixed this with my filament transformer at least

 

[jcalvarez]

12V unloaded is definitively wrong for such a transformer. I just tested a 50W 230/6V toroid, with 240V mains, expected ~6.3 at full load (~8A). I get 7.41V at no load, 6.5V at 6A (1 ohm) load.

 

[wg_ski]

Is the HV reading proportionally higher, too?

That’s why I said to load test the HV. It may drop a lot more than the filament winding.

 

[nigelwright7557]

You’d be surprised just how hard you can hit a tube heater. 12 volts isnt instant death.

7V is about right - I typically design for 6.8 with 122 in when custom winding power trafos. When it comes down 10% it’s about right.

I once built a valve mixer.
It wasn't working right so I increased voltage to B+.
It wasn't until I reached 25 volts that I suddenly realised the 12VDC heaters were running off the same rail !!
The heaters survived ok.
I found some valves would run off 12VDC B+ but others wouldnt.
I had to positively bias grid to make the valve work with 12VDC B+.

 

[lcsaszar]

I had to drop the 6.3V for the output tubes, too. The raw 7VAC was perfect for a Low Drop Regulator to create 6.3VDC for the small tubes.

 

[JMFahey]

Was it a mixer or an effects pedal?
Because extremely starved tubes at mere 12V are great for Guitars, not so much for clean Audio.

 

[wg_ski]

Current-starved at a more reasonable operating voltage are “better”, even for guitars. Running a 12AX7 at 12 to 30 volts is often more of a useless gimmick than anything else. “Look, it’s got tubes, and it’s BLUE!” And just as likely to be used for “clean audio”.

 

[mdpaudio]

Put a known 6.3vac on what should be the 6.3 winding and measure the input leads to see what the transformer is expecting to see. That will verify things for you. If the HV windings are unloaded the LV will be higher than expected.

 

[lucat]

Hi, sorry for not answering. Life got in the way.
Finished the wiring and hooked up the HV and now the voltage is spot on at 6.26v!
Sorry for the fuss, guess it was for nothing. It had never happened on other transformers (wound by the same company), so I was slightly worried.