Power transformers - OK to use 240VAC primaries with a 230VAC power outlet?

[motzu]

Hello,

I'm thinking about using Hammond power transformers for my next build (specifically, I'm looking at the 291AEX and 291BEX models, spec sheets here: Hammond Mfg. - REPLACEMENT & UPGRADES - Tube Guitar Amplifier - Power Transformers).

But all my appliances use 230VAC, in my 5F1 build I've used the 230V primary, and my power outlet puts out a measured 225VAC, and those Hammond PTs only come with 240VAC primaries.

Would I be taking a chance in using a power transformer like that with my 225VAC system?

[Enzo]

Transformers don't have voltages, they have ratios. The secondary voltage output of a transformer will be the rated voltage ONLY if the primary voltage is correct, and then only when fully loaded. If that voltage varies, then so does the secondary.

It won;t hurt the transformer to run it a few volts low.

Is your mains voltage ALWAYS 225VAC or does it vary up or down through the days and weeks? Around here, the voltage s change, and on very hot days when many air conditioners and fans are running, the mains volatge can drop very low.


225v on a 240v primary is 15v low, about 6%. That means all your secondary voltages will be about 6% low also. So the 6.3 would run about 5.9 if you load it to full current. 5v would drop to 4.7v. and the 650vCT would drop to 611. if you don't ask full current from those windings, then those voltages will be a little higher. That B+ drop would be then about 30vDC.

I leave it to you if those changes are within your useful margins.

[motzu]

Thank you for the quick and informative reply! About the B+ drop, maybe I've missed something, but I'm guessing you meant to say "about 300VDC"?

[motzu]

Sorry, I forgot to answer your question. The mains voltage does vary here too, and since today has been a very hot summer day indeed, I expect that it might even go higher than 225VAC. So perhaps the 240V rating for the transformer primary isn't that far off. I'll take my chances with the Hammonds. Thanks again!

[Wakculloch]

Is there no-one local who has transformers in stock, or who could wind one to your specification. Seems a strange idea to have something sent half way round the world that is essentially incorrect for your application.

[motzu]

I could get a different PT or have one wound for me, but I've had a few issues in the past with PTs getting too hot, and those Hammonds are allegedly built to run cooler and last longer. And Hammond seems to be a well-respected transformer brand. If you can point me to another Hammond PT with the same dimensions (and correct secondaries) as the two models I've mentioned in the original post but is designed for 230VAC, I'll get that instead.

Based on the previous calculations, I'd say I should most likely be fine with the 240VAC PT. Hopefully .

As for halfway around the world, I'm not sure where you picture Romania to be, but there are Hammond dealers in Germany, which is only about 2-3 countries away in a straight line . It's no further than Colorado is to Nevada, and people in the US usually think nothing of ordering from another state (and the paraller holds even better because both Germany and Romania can be thought of as European Union states).

[Wakculloch]

Sorry, I was imagining something being sent from America. But that does bring up another question, in that the standard European mains voltage has nominally been 230V for many years and one would think a company who distributes in Europe should know that. I'll shut up now cos i can feel myself digging a deep hole.

[motzu]

You're absolutely right. Maybe since they're Canadian they're somehow more sympathetic to the UK 240VAC power system?
Perhaps there's some technical consideration behind their decision, but as I've already made it abundantly clear, I'm no transformer expert so I wouldn't know.

As a side note (although Harmony Central reviews are what they are), here's someone who has replaced a Tube Amp Doctor PT with a Hammond and seems happy with the choice (Harmony Central® - User Reviews):

"there were problems with the main transformer
it was a model which became very very hot and produced a extraordinary loud hum.
I send the amp to tad- they checked it but refused to trade this transformer. everything would be allright .the trafo would be able for amp modifications and therefore would be "stronger".
I bought a hammond trafo and now its perfect."

Since this person doesn't sound British, and you wouldn't buy a TAD kit in the US, I assume the mains voltage where he/she lives is 230VAC .

[Enzo]

300volt DROP? no.

If the B+ winding is 650v center tapped, that is 325vAC per side. rectified and filtered that makes about 460VDC.

If I lose 6%, that drops my AC voltage to about 305VAC, which yields about 430vDC. SO the net reduction is about 30VDC, 460 to 430.

And to do it the other way, if I start with 460VDC and reduce it by 6%, I get about 430VDC.

That assumes a solid state rectifier.