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Author Topic: Question about running FL2100B at low plate voltage  (Read 6932 times)
KZ4T
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« on: April 29, 2010, 05:04:30 PM »

I recently purchased a used FL2100B that was DOA.  I used the low voltage (425 volt) tap on the power transformer while repairing the unit and then moved to the mid voltage tap (620 V).   I get about 400 watts (approx 1600-1700 Vdc)  at this tap, which is plenty of power for my purposes. I would like to leave the amplifier at this plate voltage level. I am driving the amp with a TS-520S.  My question is this.  Are there any special percautions, or unintended consequences that I should be aware of ?
This is my first amplifier and my amplifier experience is very limited.

Jon
KZ4T
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WB2WIK
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« Reply #1 on: April 29, 2010, 07:32:05 PM »

Why wouldn't you run it at full voltage?

The advantages are numerous, not just running more power.  The amp has better linearity and lower IMD products when run in the "SSB" position, which provides higher plate voltage.
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KZ4T
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« Reply #2 on: April 29, 2010, 08:43:00 PM »

There are a couple of reasons I prefer to run the lower plate voltage, other than the fact it is sufficient power for me.  One reason is that I do not have 220 volt power in my shack and if I run full power it pushes the 110 service.  The other reason may not be legitimate but I felt that operating at lower plate voltage might increase the life of the 572B tubes.  You did elude to a couple of technical issues I was not aware of.  Linearity and IMD not as good.  Thanks
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WB2WIK
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« Reply #3 on: April 29, 2010, 08:46:41 PM »

The tubes won't last longer at lower voltage.  Either they can withstand 2400V (which they should), or they can't.  If they're going to fail due to the higher voltage, that would happen quickly and it means the tubes are defective.

Everything else will run better at higher voltage, and likely last longer because you'll be within the design parameters of the tank circuit.
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W1QJ
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« Reply #4 on: April 30, 2010, 03:40:13 AM »

Actually it is NOT true at all that running reduced voltage will eliminate stress on the 110v line!!  It is just the opposite in fact.  On 110v lighting circuits which is probably where you have the amp plugged into, the major factor involved with stressing the circuit is NOT voltage but rather CURRENT!!  By running the amp at lower voltage, it takes more current to produce 400 or 500 watts than if you used high voltage.  At higher voltage it would draw much less current on the 110v line to produce the same 400-500 watts.  So consequently you are in fact stressing the circuit more than if using the higher voltage.  I think you had better up that voltage.  The simple power formula makes this obvious.....P=EI
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AD5X
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« Reply #5 on: April 30, 2010, 05:19:13 AM »

"At higher voltage it would draw much less current on the 110v line to produce the same 400-500 watts."

Changing the internal amplifier's power supply voltage for a given output power does change the current requirements of the internal power supply.  But it doesn't affect the 120VAC input current.  Like you said:  P = EI.  For a given RF output power, the input AC power stays constant (neglecting any amplifier internal power supply losses).  The way to reduce 120VAC input current is to go to 240VAC.

Phil - AD5X
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KZ4T
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« Reply #6 on: April 30, 2010, 06:53:08 AM »

I appreciate you guy's comments and I agree, assuming the same 400 watts power level.   However, I believe the proper way to tune a amplifier, even if you intend to operate at lower power, is to tune for maximum power and then reduce the drive power.  At maximum plate voltage and power, the input 110 volt, 60 Hz line current becomes 18 amps , which exceeds the 15 amp rating of my wall receptacle.  I had hoped to avoid this situation by operating at lower plate voltage and  keeping the maximum power down around 400 watts or so.   However, based on the comments of some of you, it appears that there are other issues that come into play. Impedance, IMD, etc.  So I probably will go ahead and use the full rated plate voltage and have a 220 volt service installed in the shack.  Who knows,  I may occasionally want to operate at full rated power if I have it available.   Thanks everyone.   KZ4T
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WB6BYU
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« Reply #7 on: April 30, 2010, 10:13:57 AM »

Even if tuned properly for maximum output power, if you are only running it at 400
watts output (by reducing the drive level) then the average current draw from
the wall outlet won't be significantly different on either transformer tap.  Just
because the amp CAN be driven to high power doesn't mean that you need to
do so.  It is only going to draw 18 amps when you are driving it to full output
power.

(Of course, you could replace your 15 amp outlet with a 20 amp one instead if
the wiring will support it.)

Actually there will be some minor variation in AC current draw from the 120V line
because the efficiency of the amplifier may be different for the same output power
and different plate voltages.  But I don't know the circuit well enough to say which
would have the lower current draw.

If you are worried about how to tune the amp at full output power without exceeding
the outlet capability, you would use some sort of pulsed waveform that has a high
peak but low average power.  It's the average power that determines the AC current
draw, and you can stay well within the limits while still generating full peak power.
« Last Edit: April 30, 2010, 10:18:03 AM by Dale Hunt » Logged
W8JI
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« Reply #8 on: April 30, 2010, 11:18:02 AM »

I recently purchased a used FL2100B that was DOA.  I used the low voltage (425 volt) tap on the power transformer while repairing the unit and then moved to the mid voltage tap (620 V).   I get about 400 watts (approx 1600-1700 Vdc)  at this tap, which is plenty of power for my purposes. I would like to leave the amplifier at this plate voltage level. I am driving the amp with a TS-520S.  My question is this.  Are there any special percautions, or unintended consequences that I should be aware of ?
This is my first amplifier and my amplifier experience is very limited.

Jon
KZ4T


Jon,

Your amplifier will be fine on the lower tap. IMD will be a little worse, but not significantly so.

The power mains draw would be no different at all if it was operated at the same power input level, but on a higher secondary voltage. Operation on 240 would reduce current from the mains, if you ever manage that.

Let's get the line voltage correct first. The USA mains voltage is 120/240 nominal. It hasn't been 110/220 since just after WW II! It was 117/234 in the 1950's and 60's, and is now 120/240 and generally higher.

That amp is really just a two tube amplifier designed for one kilowatt DC input. That's only about 9 amps from a 120 volt power line. I'm not sure why you think it would draw 18 amperes, but that is totally wrong. If you had that amp drawing 18 amperes at 120 volts, the power input would be over 2000 watts.

The tubes only dissipate 160 watts each.  If you ran 18 amps from the mains, that would be 2200 watts. If 2000 of those watts were available for the tube anodes, output would be about 1100 watts or less. The tubes would be dissipating 900 watts, or about 450 watts per tube in a 160 watt rated tube.

Why would you want to run an amplifier with 160 watt dissipation tubes with 450 watts dissipation?

Why would we want a ~1 kW INPUT power amp to be operated at twice the design power???

Running a FL2100 on 240 volts at 9 amps, or running it at 18 amps line current on 120 volts, is hammering the amplifier a lot more than the light socket. Better have a bucket of water to throw on it when it catches fire! Doubling the power is not good.

Maybe they lie in the manual and tell you it is a 2kW DC input amp? Something must be wrong somewhere.

73 Tom



 

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W8JI
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« Reply #9 on: April 30, 2010, 07:29:18 PM »

If you choose to run say 400W PEP, the most efficient operating conditions (which leads to least line current) is with the tubes running on rated voltage and the output network adjusted to maximise linear output at that power level with least Vgk drive voltage. You may not be able to optimise the network on the lower bands because the design assumes operation at rated power. (Good practice is to slightly over-couple the PA from the operating point describe above.)

Sounds to me that the real problem is not the PA, it is inadequate mains power.
 
Owen

Owen,

The FL2100Z is rated at 1000W DC input CW, and 1200W pep.

I think what is scaring or confusing him is the 18 amps they say in the manual for 100-117V operation.
At 1000 W CW input the 2100Z should only draw about 10-11 amperes on our mains voltages. Our mains voltages are nomally over 120V.  18 amperes is a bit silly, but that is what the manual says so that is probably where he got it from.

Most USA outlets should handle the FL2100 at rated power on 120 volts.

73 Tom
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WB2WIK
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« Reply #10 on: April 30, 2010, 10:36:35 PM »

I don't know why this amp would draw more than an SB-200, it's a similar circuit.

My SB-200 draws about 10A from a 120V line, at full power, using the "Kill-A-Watt" commercial meter (1240VA indicated).

If Yaesu actually printed "18A" in their manual (I didn't look and don't have it) it sounds like a typo.

I do recall early Japanese manuals had a lot of mistakes.  They're better today.
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N5QMG
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« Reply #11 on: May 01, 2010, 04:18:50 AM »

Owen,

The FL2100Z is rated at 1000W DC input CW, and 1200W pep.

I think what is scaring or confusing him is the 18 amps they say in the manual for 100-117V operation.
At 1000 W CW input the 2100Z should only draw about 10-11 amperes on our mains voltages. Our mains voltages are nomally over 120V.  18 amperes is a bit silly, but that is what the manual says so that is probably where he got it from.

Most USA outlets should handle the FL2100 at rated power on 120 volts.

73 Tom


I have an fl-2100b.  It came with a 10A fuse installed and wired for 110/117/120 operation.  It can easily develop over 1000W input power plugged into a 15A circuit that also shares a window unit A/C.  The A/C draws well under 500W (according to kill-a-watt) at full tilt and only 65W when running the fan only.  I'm quite sure that the amp draws less than 10A since the fuse has never blown.  I can talk all day with the A/C cycling on and off and never once popped the 15A circuit breaker.  I also have my rig on the same circuit.  Average draw on the whole circuit is less than 5A.  I know it's not ideal or even desirable to run this way.  It will be corrected when I run a dedicated circuit for the amp.  The point is that the circuit is not overloaded even with all this stuff on it.  If I was running FM, it would be a different story.  ;-)  I did replace all the outlets on this circuit with good quality new ones.

The owner's manual does indicate that the amp needs an 18A supply for 110 operation and to use a 20A fuse in the holder.  I have in-rush limiting mods installed in my amp so maybe that helps a little when I power it on, but the 10A ABC fuse in the amp has never blown.  It looks vintage and I believe that it is a "fast acting" fuse.  Yaesu went a tad overboard and the OP should run his amp at full voltage IMO.  That would take less plate current to develop the same output power.  That would seem to be the least stressful on the tubes.
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