Are Hammond power transformers good enough ?

[lowtherdream]

I am building a zenclone and many are using the Hammond 272FX mains transformer.
Are there better choices that will make a difference on the output or overall noise ?
Angela is selling an interesting option ...
I have finally selected R-core from Softone for my outputs but still did not decide on the main beast

[kevinkr]

2xx series transformers from Hammond tend to be quite noisy (buzz) and run rather warm. I'd recommend the 3xx series which are quiet and run much cooler. Many other options probably exist as well.

[rdf]

Also be aware they appear to be designed for a nominal 110 VAC utility. Every Hammond power transformer I own runs high, typically 6.7-6.9 VAC filament. I don't mind as it provides the opportunity to RC filter the filaments with small dropping resistors.

[kevinkr]

The 3xx series have dual primaries with multiple taps which generally allows you to get reasonably close.

For reasons of economy (to reduce copper usage, etc.) modern transformers are generally designed to produce their rated output voltage only at the specific load for which they were designed and at the nominal line voltage. A few additional turns are usually added to a secondary to compensate for copper losses at the rated load thus allowing the use of smaller wire. (more heat too of course) Lightly loaded of course the effect of the dcr will be lessened and the output voltage will accordingly be higher.

Some vintage/mil transformers were designed with very low winding dcr and exhibit better regulation over a range of load currents than is the case for cheaply made modern transformers. The price for this is a larger, but cooler running (and more expensive) transformer for a given current rating.

[Poindexter]

The 372 is not a lot more expensive, has a bias tap on the B+ winding, runs cooler and quieter, and has dual 100-110-120 primaries, so you can adjust your voltages somewhat. I use them for test rigs, they're okay.

Aloha,

Poinz

[Tweeker]

An AnTek toroid is another option. Angela's private label PT looks quite nice too.

[rdf]

Hi Kevin. While you're right, in the case of the Hammond transformers on my bench it's a rock/hard place situation. My experience is loading just the filament winding to rated current isn't nearly enough. A modern Hammond fully loaded on all windings however will run red hot due the economic considerations you outline. In comparison, the Antek toroid I bought recently, or the 40 year old AMI/Rowe jukebox iron that makes up my current daily listen, all put out very close to 6.3 VAC fil. Given how dramatically sensitive tube life is to filament overvoltage I would never use a Hammond PS tranny without careful measurement and consideration. The multiple tap primary models would also be first choice.

(Toroids have they're own set of issues but I'm fortunate to have a local utility with no DC on the lines and view it as an opportunity to play around with RF power supply filtering. Lemonade!)

[jon_010101]

So, kinda on topic, how about the bigger Hammond Chokes?

Do they mind being used for choke-input? Buzz much?

[Miles Prower]

"Are Hammond power transformers good enough?"

I used a Hammond with a 550Vct / 150mA secondary operating at something like 180mA with a +/- SS power supply. Since this one also has a 5.0Vct / 3A secondary that's not being used at all, and a 6.3Vct / 6A secondary that's supplying 15mA for a panel LED (I prefer to power up the heaters separately) the primary is still well within its VA rating. It doesn't get all that hot even after hours of use. Wouldn't recommend overloading if you're gonna draw significant current from the heater windings as well as the HV sec., however. Otherwise, there aren't any problems with either heat or noise.

For this particular application, Hammonds are "good enough".

[dsavitsk]

Originally posted by Poindexter
The 372 is not a lot more expensive

For barely any more money, you can get a custom wound transformer from Electra-Print that will be exactly what you want.