I don't want to use an outboard step down xfmr but rather replace the 240v/50hz PS transformer in the tube amp I have with one for 110v/60hz. I don't have any cooperation from the mfr of the amp, not sure I can get a schematic for it either. how doable is this?
Have you checked to see whether there is a dual primary? What brand/model is the amp?
The higher US line frequency is fine, if you can rewire dual primaries from series to parallel.
Bear in mind that there are several secondary windings needed that may be difficult to find
when trying to change out the transformer.
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You only see 110V here if there's a problem, like the local step down transformer going bad.
> You only see 110V here if there's a problem, like the local step down transformer going bad.
Or if my dryer and water-heater are both running (on my too-long line from the street).
Since light-load here is 125V, I don't design/tune for 110V.
110V has not been "standard" in over 50 years. 117V was nominal for a long time. Then 120V, often floating to 125V 97% of the time.
I did once work in a 1970s building which was tapped specifically for 117V. Worked fine. Until a backhoe down by the river took out one of two substations for the city. They ran the city on reduced voltage for 2 years. But nobody came in my building and re-tapped the building transformer. So my lab lived on 108V for quite a while. Most things ran OK. All the PCs/servers ate it fine. My 'scope did not like it (the regulators were designed on slim margin and dropped-out). Any work I did on tube amps had to be re-figured for a 120:108 difference (13 Watts observed was probably 16 Watts on normal power).
Anyway, an external stepdown transformer IS usually the safe path for EUR amps in the US. If a factory-spec replacement PT is available, affordable, that may be better if the amp will never leave the US. But sounds like that's not the case.
Or if my dryer and water-heater are both running (on my too-long line from the street).
Since light-load here is 125V, I don't design/tune for 110V.
110V has not been "standard" in over 50 years. 117V was nominal for a long time. Then 120V, often floating to 125V 97% of the time.
I did once work in a 1970s building which was tapped specifically for 117V. Worked fine. Until a backhoe down by the river took out one of two substations for the city. They ran the city on reduced voltage for 2 years. But nobody came in my building and re-tapped the building transformer. So my lab lived on 108V for quite a while. Most things ran OK. All the PCs/servers ate it fine. My 'scope did not like it (the regulators were designed on slim margin and dropped-out). Any work I did on tube amps had to be re-figured for a 120:108 difference (13 Watts observed was probably 16 Watts on normal power).
Anyway, an external stepdown transformer IS usually the safe path for EUR amps in the US. If a factory-spec replacement PT is available, affordable, that may be better if the amp will never leave the US. But sounds like that's not the case.
thanks for the replies. its a Beard P35, I found a schematic online for the first vers and mk II. Im not sure if it has dual primaries, I dont have the amp in my hands in enroute to me now. my other thought was adapting the 120v PS xfmer from a ST-70 kit amp.
use a Mains Bulb Tester to power ON.
If the bulb flashes briefly and goes to dim, or OFF then you know the transformer is drawing a very low current.
If the bulb stays bright, then you know the transformer or wiring is drawing a large current.
Changing the primary wiring from series connected to parallel connected can be complicated and it is easy to make a mistake. ONLY power ON via the Mains Bulb Tester until you are sure you have wired it up correctly.
If the bulb flashes briefly and goes to dim, or OFF then you know the transformer is drawing a very low current.
If the bulb stays bright, then you know the transformer or wiring is drawing a large current.
Changing the primary wiring from series connected to parallel connected can be complicated and it is easy to make a mistake. ONLY power ON via the Mains Bulb Tester until you are sure you have wired it up correctly.
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