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I have a chance to get a 1 kW amplifier with a 220V plug dirt cheap from a friend of mine, but I only have a 110 outlet. The 110 outlet is on its very own 20A breaker with no other outlets. Could I run a 110-220V step up converter with the amplifier with no issues? Thanks

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    $\begingroup$ If it's really the only outlet on the circuit, probably not that big of a deal to just switch it to 220V... $\endgroup$ – Phil Frost - W8II Feb 11 '19 at 21:00
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    $\begingroup$ This question about house wiring might be better asked at electronics.stackexchange.com or dyi.stackexchange.com. $\endgroup$ – Mike Waters Feb 11 '19 at 21:04
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    $\begingroup$ I would not suggest a 120>240 converter. It should be rewired it per @PhilFrost-W8II 's comment. $\endgroup$ – Mike Waters Feb 11 '19 at 21:06
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    $\begingroup$ BTW, in the USA the voltages are not 110 or 220. Add ten volts to each number. ;-) $\endgroup$ – Mike Waters Feb 11 '19 at 21:07
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    $\begingroup$ Or the amplifier might be rewired to work on 120 V. It used to be common. $\endgroup$ – Jean-Marie Feb 11 '19 at 21:44
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120 volts times 20 amperes = 2400 watts. That would mean this amplifier would have to be more than 42% efficient to avoid popping the breaker. That's pretty unlikely. Check the specs for the amplifier to get its current requirements, then double it to account for the voltage conversion, and add some more for converter inefficiencies.

A voltage converter that can do 20 amps isn't going to be cheap anyway.

If this is the only outlet on the circuit, I'd recommend rewiring the circuit for 240V. That will give you more available power and you won't need to buy any additional equipment to convert voltages. It's likely possible without pulling new wire, so shouldn't be too expensive even if you have to hire a professional electrician to do the work, as long as you can make room in the service panel.

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    $\begingroup$ Power is voltage times current so you will have 4800 watts available not 9600. $\endgroup$ – Jean-Marie Feb 11 '19 at 21:51
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    $\begingroup$ @Jean-Marie derp. you're right, thanks for the correction. $\endgroup$ – Phil Frost - W8II Feb 12 '19 at 0:57
  • $\begingroup$ Multiply the product of I x E by the a-c power factor (PF) of the load, to find the true value of the power dissipated in that load. Load current for a given power consumption and line voltage will be higher than for a PF of unity. $\endgroup$ – Richard Fry Feb 14 '19 at 11:38
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Most homes have 220v service, but many are not wired for it. That is, there is 220 at your junction box, but not throughout the house. You would be better off to have a licensed electrician come in and provide a 220 v circuit for your amp. Warning about the amp - if it is an old, tube based amp, then you would want to get it looked at by a qualified repair person. Is the amp in use currently (no pun intended) ? If so, then you could just install it. However, it seems that few people give away good equipment ("dirt cheap"), so I would imagine that the amp has been sitting in someone's basement for years. Better get it looked at. Maybe replace the electrolytics. Ironically, I also have a SB220 for sale, thru my local ham club. 73, Joe

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You could use a voltage converter, but like Phil (W8II) is pointing out, the old $P = IE$ formula means that for the same wattage, if you half the voltage, you double the amount of current needed.

I am not sure which amplifier you have, but let's assume it is one like the Ameritron AL-80B. It is a 1KW amplifier. They claim it will put 1000 Watts on SSB (which usually means peak-to-peak) and 800 W on CW. You can get in either 120 or 240 VAC. At 120 VAC, it draws 12 amps which is 1440 watts input power. Let's assume it is putting out 1000 W. That would be 70% efficient, which is exceptional! On CW, it puts out 800 W (more realistic), which would be 55% (800/1440) efficient and is more of the norm.

For a full 1000W on CW, that would be (at 55%) 1800 watts. 1800/120 = 15 amps. Now you are starting to push the limits of a 20A breaker (see circuit breaker ratings for more info on how they are rated). As you start to get without 80% of their ratings, you can start to get nuisance tripping because you current draw will pulsing with voice peaks or CW tones. These peaks with a heavy current draw will also start causing you house lights to dim or pulse - drove my wife nuts! I had to go to 240V! At 240V, you only need 7.5 Amps. Much, much less dimming of the lights also!

You could do one of three things:

  1. If you want to try the amp out, plug it into your clothes dryer outlet (if it is not too far away) and see how it affects the lights. That would let you see how happy it is running on a 240V circuit. You could "share" the connection, if you aren't drying clothes while you want to operate - or even better - you have a gas dryer!

  2. If you are a good electrician or know a good one, wire a 240V line to your shack and make everyone happy.

  3. What most of us do - get the 600-800 Watt version, which is usually 120V at about 8-10 amps. 800 W PEP is 8x power (over 100W), which is a 9db gain! Double again to 1600W output is only another 3 db (diminishing returns).

But, I would have a really hard time turning down a "cheap" or nearly free 1kW amplifier. I'll bet the money you would save would easily pay for a licenced electrician to run a single 240V 15 or 30 amp outlet! So, I would recommend door #2!

Ayway, hope to hear you on the air with a fine, strong signal!

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