Hello all,
Henderson vintage transformers:
Was lucky in being able to buy two on Ebay without too much competition.
However, have been searching for manufacturer's information and nothing found.
One is 385v HT with 5v and 6.3 volt secondaries and the other is 240v HT also with the two secondaries.
Would like to know their VA rating if nothing else.
No idea what Radio they were out of.
Any assistance would be appreciated.
Thanks.

Smokey

Would like to know their VA rating if nothing else.

Can't help with the specifics, but found the following article about estimating VA value online. I haven't verified it against a known transformer, but may well do when I get a chance:


The VA rating of a transformer can be estimated from the size of the core and its operating frequency. You'll need to measure (or estimate as closely as you can) the cross sectional area of the center "leg" of the core (if it has a center core and two outer legs) or one of the legs (if the core only has two legs and no center core).

If your transformer is connected directly to the power mains, the operating frequency ("F") will be either 50 Hz or 60 Hz depending upon where you live. Multiply the length and width of the core's cross section (in inches) and multiply them to get the core's cross sectional area ("A", in square inches).

The estimated turns/volt can be estimated as:

X = 10^8/(15.77*F*A*13000)

The VA capability can be estimated as:

P(in VA) = (A*F/9.6)^2

For example, suppose the center leg of your transformer measured 1 x 1 inch and it was designed to operate off 60 Hz. Then:

X = 100,000,000/(15.77*60*1*13000) = 8.13 turns/volt (Useful if you want to rewind the secondary)

and

P = (1*60/9.2)^2 = (6.521)^2 = 39.06 Volt-Amperes

Assuming your secondary voltage measurement was in RMS volts, then you can estimate the RMS current of the winding by taking your calculated VA and dividing by your measured voltage:

Estimated amps = P/V

Source:
"Practical Transformer Design Handbook" by Eric Lowdon, ISBN 0672216574, Howard Sams and Co., 1990.

I have a Henderson in a PSU. I still have it's box. I think it is a 385 -0 - 385 Two 6.3V windings one I think is centre tapped and a 5V winding.

It actually has the LV currents on it's tag board This one is also a sheilded type. So one wire will appear to have no owner (open). That is the shield and is earthed.

Marc

GTC,
Thankyou and will do some calcs using your information.

Marcc,
Now what you have is interesting as I have a similar transformer here in a stamped rounded metal case painted steel blue marked '1805A' that has the same wire - looking to be o/c.
Have not applied Mains to this one as yet as I was also after further informartion.
Thankyou both for your help.

Smokey

GTC,
Thankyou and will do some calcs using your information.

Let us know what the estimate works out as.

Hello GTC,
Came out at 380VA where I had estimated from others at Jaycar as being between 150 and 175VA.
There are 3 dimensions related to the core and this one worked out as 2"x1.5"x1.25" and I hope I have not misinterpreted your guide.
Tried to find the book to extract the page for confirmation but not available.

Smokey

The one I have is black, with only one bell. (Through chassis mount)

I have a suspicion the these are American?

Marc

Smokey,

It's not my guide. As originally mentioned I found it online.

If, as Marcc suspects, it's an American transformer, and it was designed for 60Hz, it will probably have a slightly lighter core weight than a 50Hz unit.

If it's American, the primary would be for 120VAC. Unless of course it's explicitly marked 230VAC. Try backfeeding one of the heater windings with 5VAC and see what the primary reads as.