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Author Topic: AL-80B on Loaded 120v Circuit  (Read 4417 times)
KL3HY
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Posts: 117




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« on: October 05, 2012, 01:29:19 PM »

Until I can run a dedicated 240v circuit for my AL-80B, I'm currently running it on a 120v circuit that already has several things on it (2 computers, room lights, power supply for HF rig).  Naturally, if I try to drive it to max output I see a voltage drop and the lights dim, computers sometimes go nuts, etc.  My multimeter shows a nice stable 120 volts AC at the outlet with the amp off, and line voltage drops to about 70 volts when pushing output power above 600 watts.

For the time being I'm limiting my output to no more than 400 watts (and frequently as low as 150 - 200 watts) but I'm wondering if I'm causing new problems by running it that low?  I've been trying to follow W8JI's instructions for tuning up where I work up to about 400 to 500 watts and then reduce my drive power.

This is my first amp, so maybe I'm just being overly cautious, but I thought it might be worth a question here.  Am I harming the amp in any way by operating it in this manner?

Thanks,
Mike
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WB2WIK
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« Reply #1 on: October 05, 2012, 01:35:09 PM »

Your line voltage drops to 70 volts?  That seems impossible.  Something's wrong with that picture.

Normally a household circuit (branch) is 15A, and you'll know if you exceed that since the breaker will trip. Wink

SSB (if that's what you're using) has a low duty cycle so you can probably run the AL-80B at "full power" on SSB (only) if you tune it up with a string of dots rather than a carrier.  A carrier at full power may well trip the circuit breaker, but a string of dots probably won't, nor will casual SSB operation.

For CW, I'd cut it back a bit.  For RTTY, I'd cut it back a LOT.
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KL3HY
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« Reply #2 on: October 05, 2012, 01:48:17 PM »

Well the voltage drop surprised me, and I have to wonder about the conductor size in that circuit.  It's one of the longer runs in the house, at about 30' horizontal run from the panel.  My house is one of about 20 small ranch styles that were all built in the same area by the same developer in 1983 and 84, so it wouldn't surprise me if the conductor size is smallish.  Regardless, I did inadvertently verify the breaker works several months ago by trying to power up an old Dentron gla-1000b that had problems.  I also did a lengthy test transmission using Olivia 8/250 and ran back to the panel and felt the breaker, and it never got any warmer than the surrounding breakers.

To clarify my tuneup method, I switch to AM, key the mic and quickly tune.  Then I'll switch it to SSB.

But no real issues for operating the amp at such low output levels?  (100 - 200 watts)
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NO2A
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« Reply #3 on: October 05, 2012, 02:11:52 PM »

Because of the voltage drop it`s quite possible to lose 400-500 volts by using 120v. The amp will work,but you might never get full rated output no matter how hard you drive it. If you only use 100-200 watts it`s hardly worth the electric for the little gain you`d get. If you could run the other appliances off another circuit and save the amp for that 1 circuit it might help.
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W1QJ
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« Reply #4 on: October 05, 2012, 02:48:55 PM »

Lets face it, when one decides to own an amplifier and pay good money for it it's only right to do what it best.  Get a 240v line and your troubles will be over.  You'll be happy and so will your amplifier. 
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AA4PB
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« Reply #5 on: October 05, 2012, 03:00:58 PM »

If your line voltage at the outlet drops from 120V to 70V that means you have a 50V drop in the circuit. If it's a 15A circuit then the wire guage is #14. You say a 30 foot horizontal run to the panel so lets add 10 feet for any up/down runs for a total of 40 feet, or 80 feet down and back. 80 feet of #14 will have a resistance of 0.2 Ohms so to get a 50V drop you would need to draw 250 Amps. The 15A breaker would trip long before that.

If you REALLY have a 50V drop then there are some bad (high resistance) connections in the lines (perhaps at the outlets). If you are dropping 50V then you have a fire waiting to happen! It's not aluminum wire is it? Aluminum wire is noted for corrosion and bad connections at the circuit breakers and the outlets - especially if someone has replaced outlets with types not designed for aluminum wiring.

The other possibility is that RF is getting into your voltmeter and messing up the reading. Testing into a dummy load rather than an antenna should help that.
« Last Edit: October 05, 2012, 03:14:12 PM by AA4PB » Logged
WX7G
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« Reply #6 on: October 05, 2012, 03:57:44 PM »

With that voltage drop I suspect the neutral wire to the neighborhood transformer has become disconnected. Your neutral return is then through your ground rod to the house next door and up their neutral wire. Time to call an electrician.
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KD0REQ
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« Reply #7 on: October 05, 2012, 04:06:14 PM »

better also check the breaker box name tag.  if it's a FPE, you may have internal bus rot issues and no-trip circuit breakers.  if it's a Zinser/Sylvania panel, everything in there may be corroded and welded, and it's not safe for an electrician to open it up to check it out without having the meter pulled.  blanket recommendation of home inspectors is to replace the entrance panel with either brand.

if it's not a panel issue, and a class-A inspection as we call it in telco (down power, open up every connection, inspect the wire and device, fix what needs it, reassemble, move on to the next until it's all scoped out) doesn't find more issues and help your lugging on the line, you absolutely need to clamp an Amprobe or the dock-sweepings wannabe around the bare ground lead coming out of the panel, too.  if it's carrying current, you need an electrician.  the electrician may need to bring in the power company if he suspects their transformer and/or drop has a bum neutral.  you should never see current on the safety ground line, that's a disaster safety backup.
« Last Edit: October 05, 2012, 04:14:36 PM by KD0REQ » Logged
KL3HY
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Posts: 117




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« Reply #8 on: October 05, 2012, 04:30:27 PM »

Well, you guys have given me quite a bit to think about here.  There is no Al wiring in the house--I've replaced virtually all the switches and outlets myself and it's all copper.  That said, now you've got me wondering if I messed something up when I replaced the outlet the amp is plugged into--something easy for me to check anyhow.  It never dawned on me that RF might be messing up the multimeter, and I think that's a very likely possibility.  One leg of my dipole crosses over the roof near where the shack is, about 30 feet above the room.  I'll try to verify if RF is the culprit this weekend.

As I mentioned in my first post, I'm only running the amp on this common circuit until I get the 240v circuit, which should be in the next month or two.

Thanks very much to all of you!
Mike
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KD0REQ
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« Reply #9 on: October 05, 2012, 04:37:12 PM »

nice thing about a > real < Amprobe current loop meter is that it's all analog.  sanity check... have it sitting on the bench and key up... if it doesn't indicate, it's not going to give you a false reading.

that's a good check with any test equipment in an RF field, btw... key up out of circuit, and if it reads anything, you will have to consider bypassing or isolation techniques.  doubly so if you clip the leads together and it still indicates non-zero.
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WX7G
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« Reply #10 on: October 05, 2012, 05:43:03 PM »

How to tell if the AC voltage is really dropping to 70 volts? Take a look at the tube filaments before and during applying RF. If the filaments dim greatly the voltage is indeed dropping to 70 volts.

Another way is to run a lamp having an incandescent bulb off the same AC circuit. If the voltage drops to 70 volts the lamp will dim greatly.
« Last Edit: October 05, 2012, 05:47:03 PM by WX7G » Logged
G3RZP
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Posts: 4389




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« Reply #11 on: October 06, 2012, 03:21:49 AM »

Get a good old fashioned VOM like a Simpson 260. That won't go mad with RF around. If the volts are really going that low, follow the advice given above.
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W8JI
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« Reply #12 on: October 06, 2012, 05:55:17 AM »

If we are going to rationalize through a power line problem, the fist thing to do is to see if the reported change makes the least bit of sense. The second would be to look at high voltage change under load because the HV  **exaggerates** any problems.  

This voltage drop in this thread should have been a big red flag to everyone. A 50 volt drop on a 120 main is impossible.

His amplifier and all the other shack equipment would be left with 58% of voltage. Every 12 volt supply in the shack would have fallen out of regulation, the radio would shut down, the lights would be someplace between out and 1/3 brightness.  The amplifier relays would drop out, the filaments would be barely red and have no emission, the HV step-start would reset and the whole amp would be running through a ten ohm start resistor (which would limit line current to 5 amps and reset the whole process).

To drop 50 volts average, his power line ESR would be about 2.5 ohms. That means a regular 5 amp outlet load would make 12.5 volts drop and 62 watts of heat in some wire or connection.

Considering even 5 volts produces very noticeable light flickering, his house would be unlivable. Imagine when a refrigerator starts.

Finally, very few digital meters read true RMS. They generally read somewhere between peak and average, and are calibrated or corrected to read what the scale indicates, based on a sine wave into whatever response they have. The filaments in the amp run on maybe a 1-2 second average of RMS voltage, while the anodes run on a ~1/4 second average of PEAK voltage.

The anode supply is sensitive to waveshape and peak voltage, while the filaments are basically immune to peak and only respond to average.

The first thing ESR or regulation problems show as is a loss of HV under load. The HV changes far more than filament heat. That's why the HV meter is the best flag for power line problems, and the filament or an external non-peak or pseudo-average meter is the worse.

73 Tom
« Last Edit: October 06, 2012, 06:19:54 AM by W8JI » Logged
W9GB
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« Reply #13 on: October 06, 2012, 06:11:01 AM »

Per Ameritron printed specifications:  AL-80B draws 12 amps at 120 VAC.

Vacuum cleaner mfg. for 120 VAC units (NEMA) are now limited to no more than 13 Amps peak current when using the NEMA 5-15P (plug).
===
IF a radio amateur desires a 1 kW or greater HF amplifier, THEN a dedicated AC circuit (and breaker) is the safest approach.  It eliminates guess work by today's appliance (non-technical) radio amateurs.
IF a new dedicated circuit is pulled, I always recommend 240 VAC , then you can handle ANY legal limit HF amplifier on the market (Plug-N-Play).

I am very aware that many radio amateur's QTH are in older homes, many with inadequate or overloaded main AC power panels.  Houses built before WW2 are especially problematic --- my parent 's house was built in 1910s, just before WW1.  That 60 amp service was totally inadequate by 1970 ... and the original knob and tube wiring was 14 AWG with cloth insulation.
SEEK the advice of LOCAL electricians that are licensed and bonded in YOUR state or municipality.
In rural areas, where skilled trades are scarce or county is below US poverty line, you must be especially vigilant with safety.  Many have been electrocuted due to "Hillbilly electricians" that do not follow NEC standards OR any electrical wiring standards.
« Last Edit: October 06, 2012, 06:22:11 AM by W9GB » Logged
K4DPK
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« Reply #14 on: October 06, 2012, 08:50:13 PM »

Ithink your AC voltage measurement is faulty.

Compare the plate DC voltage key up versus key down.  If your line voltage really has that sort of drop, so should your high voltage.  That is your HV should fall from about 3 kv to around 2 kv.

Phil C. Sr.
k4dpk
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