Hammond 291AEX PT voltage checks

[sterling59]

Hi guys,

Relative newbie question:

I have a Hammond 291AEX PT I'm looking at using to build a PR clone. I wanted to check the voltages against the spec sheet prior to starting the build (https://www.hammfg.com/files/parts/pdf/291AEX.pdf)

With 120.3 VAC input on the primary and no other connections, I'm only getting 2.73v (5 volts expected) across the yellows for the heater circuit and 3.36 (6.3 volts expected) across the greens for the filaments (this tranny has a CT for the filaments but it's not hooked up as the tranny is simply sitting on the bench). I'm getting 345v across the red power cables. (expected 325v)

Are these voltages low because they do not currently have a load or is the transformer defective?

Thanks!

[xtian]

Sure sounds like you're measuring incorrectly--you report exactly half the voltage I'd expect from an unloaded PT. Are you connecting one lead to each yellow wire? Should be about 5.5vAC for the yellow pair, 6.6vAC for the heaters, and 650v for the red (though your meter may not go higher than 500 or 600v). Are you, perhaps, measuring with one lead connected to a center tap?

[sluckey]

You should have 650VAC between the two red leads. All your secondaries are reading half what they should be. I suspect you have the primaries configured for 240VAC operation and are only applying 120VAC.

[JPK64]

Good call Sluckey. That sure lines up with what he's reporting. 120V across 240V taps will do exactly that.

[sterling59]

Ding, ding, ding!!!

We have a winner... I had the two 120v windings in series instead of parallel which would be fine if I had 240v input....

Thanks Sluckey!