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Author Topic: Amp and 250v  (Read 4271 times)
K3SZY
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Posts: 31




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« on: October 04, 2010, 05:54:19 AM »

I have always run my amp on 120v for I never had another line installed in my shack.  Now I have installed a new line which is 250v.  The amp manual I have says it is able to run on 117, 200 or 235v but I will have a measured 250v available at the outlet.  My line comes in from a pole peg transformer on a pole in my back yard.  Is the extra 15v within upper acceptable limits to run the amp?
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K6AER
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« Reply #1 on: October 04, 2010, 02:19:16 PM »

You didn’t mention the amplifier and that would help.

The difference from 235 to 250 volts is about 6%. If the tube is a ceramic it will make little difference. For throated tungsten tubes like a 3-500Z, most have limits of +/- 5% on the filament voltage. As the filament voltage increased you will get more emissions but the tube life can be shortened. You can add some series resistance to bring the filament voltage down if the filament voltage is too high.

Go to Tom’s Web site, W8JI and he has a load of useful information about tube amplifiers.

http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm

73, Mike
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KB1LKR
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Posts: 1898




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« Reply #2 on: October 04, 2010, 05:18:37 PM »

Thorated?

If your running 250V line-to-line then you're likely running 125V from either line to ground, so same problem would exist at the 117V setting as the 234V (or 235V) setting of the amp.

The pole pig (or something upstream?) may be tapped a bit high -- can you get the utility to tap it down closer to the US nominal 240/120V? (probably not?)
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K0ZN
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« Reply #3 on: October 04, 2010, 07:05:38 PM »

I agree with KB1LKR....  I would contact the power company. 250V is pretty high; that could be hard on consumer electronics.  What kind of line voltage are
your neighbors seeing?  My understanding is that 220 to 240 is the norm. Not trying to be flippant, but is the meter you are measuring that voltage with calibrated and accurate? You want to be sure your measurements are correct before you make a complaint.

Tubes are too expensive to be running high filament voltage on them.

Bottomline: Either you or the power company need to come up with a way to reduce that line voltage or change transformer taps in your amp.

73,  K0ZN
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K6AER
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« Reply #4 on: October 04, 2010, 09:02:07 PM »

Actually 250 volts is pretty much the norm for home delivery. Motor devices (air conditioning) will start much better with 5% more voltage than 5% less voltage. The power company is doing you a favor.

The amplifier is not that sensitive to a little over voltage. The Americas have been on a 240 Volt AC minimum for over 35 years.

If you are that concerned about the filament voltage put some series resistance in series with the filament line if it is over the the maximum for the tube. Five percent change in the primary voltage is not going to effect the high voltage supply or general amplifier operation.

it would still be helpful if we knew what the amplifier model number is.
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VR2AX
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« Reply #5 on: October 05, 2010, 06:15:58 AM »

I don't think the amp will care too much about the extra 10% voltage externally, provided in other respects it is treated in a decent manner. If you want to be ultra cautious you could mentally reduce your tune and operational readings in the same proportion, but it will not make a huge difference.

It may also be worth checking your voltage regulation over time, in fact your utility should provide such information to you upon request. There should also be a regulator that you could check in with, hopefully.
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WB2WIK
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« Reply #6 on: October 05, 2010, 09:44:35 AM »

Actually 250 volts is pretty much the norm for home delivery.


I agree with that.  Here in my area (Los Angeles) line voltage is typically 250V, especially in the hottest summer months when the utility "cranks it up" purposely to allow for the added demand of everybody running air conditioning all the time.  During the winter it runs a bit lower, when they don't do that.

But it's always over 240V.
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KB1LKR
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« Reply #7 on: October 05, 2010, 10:04:50 AM »

ANSI C84.1 specifies 120/240V as nominal for 3 wire (single phase) service w/ Range A (normal operating conditions) tolerance of +/- 5% (114-126V & 228-252V), so if you are indeed at 250V, you are just barely in range.

A desirable target would be to  234-246V (117-123V), but, assuming a calibrated, traceable (e.g. to NIST) meter and consistency of the voltage day to day and at various times of the day, whether you can get the utility to drop you down ~10V line-line (to ~240V) is another question.

That the amp's highest tap is only 235V is another potential problem. What's your measured filament voltages (key up & key down) at the tube pins w/ a calibrated meter & what tube(s) are employed?
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AA4PB
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« Reply #8 on: October 05, 2010, 10:32:57 AM »

Mine is 250V and the power company refused to lower it. I used to go through a lot of electric dryer elements until I found out that I could order elements rated for the higher voltage.
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K3SZY
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Posts: 31




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« Reply #9 on: October 06, 2010, 05:11:59 AM »

The amp is a Command Tech. 144 mhz Commander II with a single 3cx800A7. It is a ceramic tube.  It is not the one made by Palstar but the original.  The transformer allows for 117VAC,200VAC or 234VAC 3 wire single phase.  I contacted Palstar and they said the 250VAC is no problem. I have not done any filament voltage tests and my meter is not calibrated.  There are no other taps on the pole peg from what I can see.

I guess I will go with what Palstar says and run it but I will check the filament voltage to see if it is within tube mfg. specs.

Thanks for all the comments.
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KB1LKR
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Posts: 1898




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« Reply #10 on: October 06, 2010, 09:48:29 AM »

Eimac data sheet says 13.5 V +/-0.6 for oxide coated cathode & 2200 VDC Typ., 2250V Max w/ signal, 2500 VDC max w/o signal (allowance for HV PS rise unloaded).
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N6PJB
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Posts: 10




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« Reply #11 on: October 06, 2010, 11:34:44 AM »

Our line is at 245 V from P.G.& E.
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K6AER
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Posts: 3515




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« Reply #12 on: October 06, 2010, 10:16:28 PM »

If it is any consolation I also have a Commander-II 2 meter amp and have been running it for over 5 yesars on 250 VAC from the mains. No problems have been encountered.

The 3CX800A7 heater voltage is referenced from Eimac at 13.5 Volts +/- .6 volts. This is a varance of almost 6%. This is within the normal varance of a typical AC mains.
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KC5AOS
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Posts: 54




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« Reply #13 on: October 07, 2010, 01:15:42 PM »

Run a really long extension cord. Grin  That'll drop the voltage.

I jest of course. Wink
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VE1IDX
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Posts: 150




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« Reply #14 on: October 07, 2010, 03:06:31 PM »

My line voltage is 250-252 volts and I have never had a problem with any radio equipment or other electronics nor have I had a problem with light bulbs. It has been this way since the house next door was built about 18 years ago. The power company relocated the pole pig transformer to the end of my driveway and ran long secondaries to each of two houses located several hundred feet on either side of me.The voltage was stepped up to compensate for the drop in the long secondary line. Interesting to hear about the fellow having problems with the dryer elements. I don't think there is anyone who uses the dryer as much as my wife and I have never blown an element.
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