Lowering transformer voltage

[Normster]

I have a 340-0-340 PT that has leads for both 120VAC and 125VAC primaries. If I use the 125VAC leads and run on 120VAC, will the output drop to 326-0-326? (calculated based on step-up ratio)

[Bob-I]

I have a 340-0-340 PT that has leads for both 120VAC and 125VAC primaries. If I use the 125VAC leads and run on 120VAC, will the output drop to 326-0-326? (calculated based on step-up ratio)

Yes, you're talking the Weber PT right? I did that on my Super Reverb and it worked exactly as you described.

[Normster]

Thanks, Bob!

My heaters were running at 6.8V so that should help that problem as well.

[Bob-I]

Thanks, Bob!

My heaters were running at 6.8V so that should help that problem as well.

Yep

[Greg Smith]

IIRC you can also reduce/increase a transformer's secondary voltage by wiring an unused low voltage secondary in series with the primary. If you wire the LV secondary out of phase with the primary, the secondary voltage is reduced slightly. If you wire the LV secondary in-pase with the primary, the secondary voltage is increased.

For example, if you were running a Hammond power tranny and weren't using the 5V rectifier filament winding, you could wire it in series with the primary to increase/decrease the voltage on the remaining secondaries.

I can't remember where I read this, and my mind may be playing tricks on me (i.e., it may be crap). Can anyone verify this?

Greg

[Funkalicousgroove]

I think you can also use a zenier diode on the CT of the HT wind to drop voltage, or do a google search on "Vintage Voltage" it's a small device you use between your AC mains and your amp to drop the incoming voltage to 110vac, and you can of course use it on any amp.

[skyboltone]

IIRC you can also reduce/increase a transformer's secondary voltage by wiring an unused low voltage secondary in series with the primary. If you wire the LV secondary out of phase with the primary, the secondary voltage is reduced slightly. If you wire the LV secondary in-pase with the primary, the secondary voltage is increased.

For example, if you were running a Hammond power tranny and weren't using the 5V rectifier filament winding, you could wire it in series with the primary to increase/decrease the voltage on the remaining secondaries.

I can't remember where I read this, and my mind may be playing tricks on me (i.e., it may be crap). Can anyone verify this?

Greg

Hi Greg, It's called buck/boost and somewhere on here I wrote an expose about it. Works nifty but it lowers both the secondary high voltage and the filament voltage as well. As long as the 6.3 remains usable it's a nifty way to go.

Dan

[Greg Smith]

Right. I remember someone referring to a "buck" winding now. Thanks for replying.

This seems like it would be quite a handy mod, especially considering the number of complaints I have heard about Hammond filament windings giving too much voltage because the primaries were designed for 115 vac.

Greg

[jaysg]

Q: 149 -- do you get clobbered ordering things from the US, beyond the exchange rate? I thought NAFTA was supposed to make that less of an issue. I like Heyboer, fwiw. I feel like Hammond could try to keep up and they don't.

[Greg Smith]

Q: 149 -- do you get clobbered ordering things from the US, beyond the exchange rate? I thought NAFTA was supposed to make that less of an issue. I like Heyboer, fwiw. I feel like Hammond could try to keep up and they don't.

Ordering from the US isn't too bad, provided you get you stuff shipped by USPS. UPS charges an outrageous customs brokerage fee. Apart from that, the exchange rate has become MUCH more favourable over the past year. I don't recall having to pay duty on anything, but I do have to pay Canadian federal tax. Overall, it's not too bad. Also there are some tube gear suppliers in Canada (Tubestore.com, Electrosonic), so I don't always have to order from the states.

Hammond has started offering a line of power transofmers with 117 volt primaries, as well as a series of "international" transformers with 100, 110, 120, 200, 220, and 240 volt primaries, so they seem to be making some effort to get current.

[eddie25]

IIRC you can also reduce/increase a transformer's secondary voltage by wiring an unused low voltage secondary in series with the primary. If you wire the LV secondary out of phase with the primary, the secondary voltage is reduced slightly. If you wire the LV secondary in-pase with the primary, the secondary voltage is increased.

For example, if you were running a Hammond power tranny and weren't using the 5V rectifier filament winding, you could wire it in series with the primary to increase/decrease the voltage on the remaining secondaries.

I can't remember where I read this, and my mind may be playing tricks on me (i.e., it may be crap). Can anyone verify this?

Greg

Hi Greg, It's called buck/boost and somewhere on here I wrote an expose about it. Works nifty but it lowers both the secondary high voltage and the filament voltage as well. As long as the 6.3 remains usable it's a nifty way to go.

Dan

Hey folks, been searching the net trying to find if anyone has tried this before and if they could shed some light on it for me? Is the explaination above correct? There doesn't seem to be too much info on it out there.

[skyboltone]

Look at it and think about it. I've done it for a variety of purposes in the Electrical trade. It works but you got to understand what it is. It bucks the INPUT voltage. So you get reduced (or increased) voltage on all taps on the secondary side.
[IMG:620:802]http://i51.tinypic.com/kvvpy.jpg[/img]

[eddie25]

So let's say that I have a deluxe reverb style power transformer for example that is rated for 115V primary and I'm not gonna use the 5V tap. I can connect the bottom (neutral) of the primary to the bottom of the 5V secondary tap and use the top of the 5V tap as my new primary neutral wire, and this will buck 5V from the primary voltage?

[skyboltone]

So let's say that I have a deluxe reverb style power transformer for example that is rated for 115V primary and I'm not gonna use the 5V tap. I can connect the bottom (neutral) of the primary to the bottom of the 5V secondary tap and use the top of the 5V tap as my new primary neutral wire, and this will buck 5V from the primary voltage?

Yes. But you won't know if it will be buck or boost until you try it. If it boosts instead of bucks then exchange the 5 volt ends. You will boost or buck by the ratio of 115 to 5 ~ 4.3% of the secondary voltage. You will also end up with a low or high filament voltage by that same ratio. This will perhaps require using a voltage doubler and a regulator for DC filaments.

Dana Hall has an elegant solution that is easy to implement and doesn't mess with the filament voltage.