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Author Topic: 120V vs 240V for amplifier  (Read 1504 times)
K3ASA
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Posts: 137




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« on: October 05, 2005, 08:34:34 AM »

I am running a Kenwood TS-570 Transceiver, and Getting the itch to buy an AL-811 or 811H, which will be my first amplifier. I noticed it comes wired for 120V operation....
For some reason, I thought that all(or most..) amplifiers required 240V operation..??
Everything I read, when getting ready to build the shack kept telling me "YOU REALLY NEED/MUST HAVE A 240V CIRCUIT FOR YOUR AMP, ETC..") So  ~  When I wired my shack, I made provisions for a 240 circuit. The cover plate is on the receptacle box, just waiting... Looks like I wont be needing it, huh?
Will the amp have longer life using 120 vs. 240? Better/Poorer/Same performance?? Probably very dumb questions, but just thought I would ask.
Comments?
THANKS!!  73 de K3ASA
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WB2WIK
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« Reply #1 on: October 05, 2005, 09:58:43 AM »

The AL-811's a pretty lightweight amp (in terms of power, and power consumption) so it does run okay on 120V.  The legal-limit amps do not.  And many (most) of the legal-limit amps don't even give you the option: They are 240V *only*.

Even with the AL-811, and more so with the AL-811H, there's an advantage in using 240V.  "Re-wiring" only takes a minute once the cover's off, so that's a non-issue.  The advantages of using 240V are:

-Allows you to use the 120V circuit(s) in your shack for other stuff safely up to 15A or so.  If you use the amp on 120V, you only have maybe 5-6A left for all remaining stuff on that line.

-As such, even if all you have on that 120V line is "lighting," the lighting is likely to blink as you key or modulate the rig/amp, which is kind of goofy even if it is safe.

-Using the amp on the same 120V circuit as other stuff invites conducted RFI (conducted by the AC line) from amp-to-stuff, and that can be annoying or sometimes even damaging.

-The amp transformer runs cooler when powered by 240V because the primary current in the transformer is halved.  This can prolong transformer life, and also provide better voltage stability for the entire amplifier, including the HV and filament circuits.

If you have a 240V line available, use it.

WB2WIK/6
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AA4PB
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Posts: 12673




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« Reply #2 on: October 05, 2005, 01:24:46 PM »

Use the 220V circuit. The amp draws half the current at 220V and so the voltage drop in the wire between the panel and the amp is only half as much.
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KB1LKR
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Posts: 1899




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« Reply #3 on: October 05, 2005, 05:59:40 PM »

for a legal limit amp, say Ameritron's AL-1500, at full power key down the input current is 15A at 240V (requiring a 20A/240V dedicated circuit to meet the NEC requirement of load not to exceed 80% of current interrupter rating (16A for a 20A breaker, 12A for a 15A circuit). Hypothetically if you could run this on 120V it would draw 30A key down --too much for a 30A circuit, so you'd need a 40 or 50A circuit, clearly impractical.

OTOH, an 811H (600W CW/800W SSB amp draws about 10A key down at 120V, getting near the limit for a 15A circuit, but acceptable on a 20A 120V circuit. On a 240V circuit however the current drops to 5A (with half the voltage drop), all around better situation/engineering practice if 240V is available.

If you have the 240V available by all means use it. The same can be said for large woodworking or metalworking tools too, e.g. table saws, lathes, air compressors, whatnot; if 240 v is available and they have dual violtage motors use the higher voltage.  
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VE7ALQ
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« Reply #4 on: October 05, 2005, 06:04:17 PM »

I have a Yaesu FL2100z amplifier (twin 572b tubes) which runs 0.5 Amps at 1900 volts key down on CW, for an output in the order of 600 watts.  Unfortunately I rent, and am unable to get Axx to 234 VAC, so I run the Amp on 117 VAC which is far from ideal.  Plate voltage drops from 2400 volts key up to 1900 volts Key Down, line voltage drops from 120 Volts key up to 114 Volts key down.  This 6 volt drop includes a 1 volt drop incurred by my IC-706mkiiG Exciter keying simultaneously.  The Amp. has a 12 volt slow-blow fuse rated at 250 VAC which has yet to blow.  I agree it is kind of creepy to send Morse Code and have the lights in the room flicker (albeit slightly).
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WA3IRJ
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« Reply #5 on: October 18, 2005, 04:09:16 PM »

...yes, or a 25 watt lamp on the desk, dimming as you call cq
I have a fl-7000 amp that will do that if I drive it to 500-600 watts out...on 117v
I also have a Swan Mk-2 that will run on either. But I can believe it will blow a circut breaker, if run at the limit on 117v. Even though the Swan manual says it will work. But I think it will heat up the power supply more as well.
JohnB/kb3lxy
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N3ZKP
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Posts: 2008




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« Reply #6 on: October 18, 2005, 04:42:58 PM »

John,

ALQ's problem, which has been explained to him several times, but hasn't sunk in, is that he has a 15 amp circuit with other stuff on it in an apartment building. Who know what the circuits are like. The last thing he needs to be doing is running an amp, in my opinion.

I regularly run an AL-80A at 750+ watts on a 120v circuit and neither my lights nor anything else dims when I tranmit. The difference is I am using a 20A circuit with nothing else on it. True a 240V circuit would be nice but I am well over 125' from the panel and the cost of adding the 240V circuit isn't worth it.

73,

Lon - N3ZKP
Baltimore, Maryland
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VE7ALQ
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Posts: 349




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« Reply #7 on: October 18, 2005, 05:20:01 PM »

With due respect to N3ZKP, I think that he is wrong about the 15 amp bit.  When I was in another QTH, I had 30 amp service at 117 VAC.  My Amplifier, then a Heathkit SB-200, still blinked the lights and dropped plate voltage to 1900 volts when powered up to the legal limit of 1000 watts DC input.  When my parents agreed to and paid for Smiley a 234 volt high-capacity extension to run between my Amplifier and the fusebox, the lights ceased to flicker, and the SB-200 plate voltage was in the vicinity of 2100 volts under load.

When I was younger I used to drive Volkswagons.  My Volkswagons had perennially poor contacts on 6 volts, the horn would fail, etc.  The last Volkswagon that I had was 12 volts, and it made a world of difference.  No more electrical problems...

In summary, there are fewer problems with higher voltage.
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N3ZKP
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Posts: 2008




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« Reply #8 on: October 19, 2005, 05:15:40 AM »

<< I think that he is wrong about the 15 amp bit.>>

Nope, not wrong.

<< When I was in another QTH, I had 30 amp service at 117 VAC. My Amplifier, then a Heathkit SB-200, still blinked the lights and dropped plate voltage to 1900 volts when powered up to the legal limit of 1000 watts DC input.>>

On a 30 amp circuit? I seriously doubt that, but then again, anything's possible I guess.
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K7UNZ
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Posts: 691




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« Reply #9 on: November 05, 2005, 06:38:02 PM »

Yes, all things are possible.....I happen to have 30A service at my house.

However, just added an AL-811 this past week, and had the electrician over yesterday to install the 220V in the shack. (that's one reason I KNOW it's 30A, 110V service...)  In fact, the guy told me that it's not at all unusual in my area.

Jim/k7unz
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N3ZKP
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Posts: 2008




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« Reply #10 on: November 08, 2005, 12:35:12 PM »

Jim,

I wasn't doubting the 30A, 120v line; we have some of those in my office building. I was doubting a 2-tube 572B amp causing lights to dim when operated on a 30A line.

Lon
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W1CEW
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« Reply #11 on: November 24, 2005, 07:31:56 AM »

I guess what I'm wondering is whether my SB-200 with these 572B's would see significantly better performance using the 240 volt line as compared to the 120.  50 watts?
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