Multitap universal primaries on power transformers?

[mike_mccue]

I am working on a project where the solution that most easily provided for the required secondaries was a Hammond 370BX.

I'm in the USA and see no benefit for all the extra primary leads.... I'm planning on using a 8 screw terminal strip to give everything a home.

Are there any downsides to using a universal design when there is no need?

It seems like two parallel circuits when wired up for 120 vAC... is that a correct way to look at it?

Is there anything especially good or bad about that?

thanks,
mike

[tedmich]

the diagram is a little confusing, looks like 2 parallel 120V with HV and bias off one and heaters and rect off the other, should work fine, you can just cap the unused primaries and forget them, but you are paying for the extra taps.

Edcor XPWR011 is pretty close a little cheaper, but lacks the bias tap I believe

[mike_mccue]

Yes, Hammond also has a version with just a 120 Primary and NO bias tap. I want the bias tap.

Here's the 370BX primary hook up:



Generic 300 series schematic:



thanks,
mike

[defaced]

Are there any downsides to using a universal design when there is no need?

It seems like two parallel circuits when wired up for 120 vAC... is that a correct way to look at it?

Is there anything especially good or bad about that?

The only down side I know of are the extra wires to deal with. You can wire the secondaries in parallel for 120v or series for 240v. The thing to keep in mind is that barring the transformer efficiency, power in = power out. So if you're going to load down the secondaries to capacity, you're going to be pulling the maximum current through the primary, which is best done when you're using the whole primary, which in this case would be to wire them in parallel.

[mike_mccue]

Thanks,

Also, I've been assuming that in U.S.A. that 120vAC is the best choice. (as opposed to 110vAC)

Is that a reasonable assumption?

best regards,
mike

[octal]

Yes! The line voltage has drifted up over the years. 110-115 was the old spec (as you will see listed for '50s era Fenders and such.) Every modern outlet I've checked has 120-127Vac.