Transformer potting

[eldarvanyar]

Hi Andy,

I have just read your post about your difficulty with noisy transformers from two companies that you have ordered. I am about to order a power transformer myself from Majestic Transformers or I could go with a Hammond. I have used Primary Winding transformers for my EAR 843P clone amp but he is not answering any of my emails.

Would you mind telling me privately the companies to avoid as I don’t want to end up with noisy transformers.

Thanks,

Lee

[bikerhifinut]

PM sent but my experiences may not have been typical.
I will say this, be absolutely firm when specifying primary voltages. The ones i bought had been wound for a nominal 230V, which is the standard for UK mains but this can vary from a little under 220V up to a maximum legally allowable 253V. In both my last locations in Rural villages, the mains has been right up atthe maximum allowable give or take a couple of volts.
To that end I would counsel on any transformer where the secondary voltage may be critical, and 6.3 and 12.6V heater windings come to mind here, to ask for Taps on the primary to allow for at the very least the higher end of the allowable mains voltage.
If the manufacturer wont, then take your business elsewhere.
Mains voltage can vary considerably.
My noisy ones were made worse in my view by having a 230V primary and frankly the attitude of the manufacturer when I queried this after having issues didnt impress me really.
Its a known issue and no manufacturer should sweep it under the table.
All said, if you have to settle on a primary Voltage, make it 240V and that way you'll most probably be just fine.
All WD supplied ones use this as far as I know and I have not had any problems with the slight overvoltage they give where the output isnt regulated.

Andy

[John Caswell]

Hi all,
The only solutions to noisy transformers is either oil filled or vacuum varnish impregnation - both expensive to do - hence little available
Higher mains voltages
Interesting that you brought this up I suffer a great deal from American and European amplifiers having very high heater voltages - due to the power tx only having a 230V primary.
I tend to fit one or two VDRs in series with the primary to at least cut the voltages down a bit.
I am on Andy's side asking for multi tapped primaries.
This is also a problem with "Wall warts" I had a very perplexing problem with several Thorens turntables where the output motor driver transistors would overheat. couldn't find reason til I checked the 16V "Wall wart" bingo 19V ac. Changed it for a 12V version all came good.

John

[bikerhifinut]

John, not only US and European gear. Most of the Chinese transformers seem to come with 220V primaries as do some early japanese amplifiers etc.
This can really give a headache with overvoltage.
Caveat Emptor as they say.

Andy

[A Stuart]

Wasn't that only on the Ides of March?
No, maybe that was Caveat Emperor.