Dealing with high line voltages

[KE6DF]

I realize we have touched on this before, but I'm curious what most people do to deal with high line voltages.

Where I live, the line voltage is usually 123 - 124 volts.

I didn't measure the voltage last summer, and it's not hot enough yet for AC use. But one issue is does this line voltage hold up all year or is it lower in the summer?

That's really too high for most tube based equipment which was built for 115 (usually).

And even HB equipment based on old transformers is going to put too high a voltage on tube filaments.

So, what do most people do when building HB:

o Plan on using a filament winding as a bucking winding on each piece of equipment.

o Build a variac into everything.

o Run all the BA and HB stuff off one large variac.

o Just live with it even if it burns out tubes faster.

One thing I've been considering is to use a 16 VCT 15a transformer I have in my junk box and build a bucking box that can then power a power strip running at 115ac. Fifteen amps would be enough for a low/med power TX and/or lots of receivers and test equipment.

But an alternative for HB units would be to build in a bucking system in each design.

Is 123-124 volts normal across the country these days, or is our PG&E (California) service particularly high?

[k4kyv]

I would use one bucking transformer into a power strip to run everything. If you plan to pull heavy intermittent loads, avoid a variac.  They substantially degrade the voltage regulation.

An isolation transformer might also work, since some of them have variable voltage taps on the primary and/or secondary, but like variacs, their output tends to sag under heavy loads.

One application that does work with a variac is to use a heavy duty filament transformer to buck the voltage, and control its primary with the variac.  That way, the variac is not taking the full current load, and voltage sag shouldn't be a problem.  Just make sure the low-voltage transformer itself has good regulation.

Of course, if you plan for light duty only, voltage sag shouldn't be a problem. I wouldn't bother with the clutter of a separate bucking transformer or variac feeding every device I had plugged in.


 

[Jim, W5JO]

Take a look at the manual for the equipment you are using.  Many say 115-117 volts AC 60 Cy.  Now in 1950s the line voltage was 115 +/- 10%.  So that takes you from 103 volts to, what, 126.5 volts.  Much, too much has been made of this kind of like the myth that if you don't rotate glass power tubes into service on a schedule, they will loose their vacuum.

Yes higher line voltage will give you higher voltages but, the equipment was designed to tolerate it.  Remember most rural lines were jacked up the 10% at the beginning so it would be over 100 volts at the end, which means that first guy would see 126 volts.  That is why they build pole pigs with variable taps to account for all that variance.  Today to save costs the transformers do not have multiple taps so the voltage is always near 125.

Also on the rural line there is a lot of noise and surges, thanks lightning and other causes.  You may, or may not, enhance the operation by bucking the line voltage or using a variac, but the equipment was designed for 125 volts.  I have steady 125 volts here and do not experience abnormal failures.

If you have trouble with that, look at the service manual for the equipment, don't they say voltage reading +/- 10% based on line voltage?  Most of this argument came about after the advent of digital meters.

[Pete, WA2CWA]

As Jim points out, given the AC voltage tolerances specified for many boatanchors, there really should be no concerns. My typical line voltage hangs around 124 volts. During summer months, it sometimes drops to around 121 or 122 volts. Never had a boatanchor issue with line voltage. I just plug them in and run them; never had one blow up from too much ~+/- 120 line voltage. Most modern day AC to DC power supplies, to power your modern rig, also have no issues operating at this voltage.

[K6JEK]

I do serious overkill mainly because I got a deal on a serious over-killer, an Elgar 6000B AC line conditioner.  It produces clean as the driven snow 115 VAC while my line voltage varies all over the place from about 115 to 126, maybe higher, and that within a span of a couple of hours.

If you find a bargain on one of these, I highly recommend getting it.  It's small but you can hurt yourself lifting it.

I do not run the high power stuff on it, just the nice old boat anchors.

I did not buy it at Tucker but here's their listing of one to give you an idea.

http://www.tucker.com/java/jsp/product_partno6000B_invid10616_condR.htm

[KM1H]

Hallicrafters, in particular the roughly 1938-50's era, have transformers that are entering saturation at 122-124V. Not all models but Ive measured plenty to know it as fact.

Running 10% high on the filaments will cause tube degradation a lot faster than at 6.3V or even better to run at 5% low. Its simple enough to do a transformer and overall internal temperature test at say 111-112V and at 123-124V, the difference is dramatic

While the published ratings may have been 105-125V I doubt if all were thouroughly tested at the high end. Now toss in 60-80 years of simple enamel wire and fishpaper insulation degradation from the heat and you are asking for trouble. Toss in some leaky caps and you are quickly begging for a replacement or sending it to Gary for a rewind.

I use bucking transformers and a 12V one was used in the example above. Each work and operating bench here for over 20 years is fed with a large bucking transformer, mostly oddball (cheap) voltages in the 10-13V and 10-20A range. With communications and consumer radios used throughout the house I use either individual 12V @ 2A xfmrs or a strip fed with something in the 5-7A range which will handle several 18+ tube consoles with 4 tube audio amps. Some consumer radios are also well known for fragile iron and Im certainly not going to do something as foolish as feeding a several thousand dollar piece with 124V.

Carl
KM1H

[Pete, WA2CWA]

The Yaesu, FT-2000, as an example, has a built-in power supply.  AC input can be 90 VAC - 132 VAC or 180 VAC - 264 VAC.

[Jim, W5JO]

Carl I agree with you if you are doing repair or refurbishment of equipment for customers, but for me I don't see the necessity.  I have two HRO 60s that has 8.? volts on the mixer and oscillator stages filaments that are attached to the ballast tube.  One of them I have had since 1998 and the tubes still work fine.  Don't ask me why, the voltage out of the transformer is very near book value to the ballast.

I found an orphan NC 183D that had a bad power transformer so I decided to have Gary/WZ1M rewind it for me just for something to do and I asked Gary to wind the primary for 122 volts just for grins.  The temperature in the cabinet didn't change  and the voltages are near book values.  As you suggest, heat is a real killer so keep the ambient shack temperature down so the heat will go away as best as possible.  Also leave at least 2 inch clearance on all sides and the bottom of radio's louvers.

Every time I see a picture of a desk with pigeon holes for equipment and the unit is almost squeezed on the sides,  or radios stacked on top of each other, I cringe.  Imagine how hot they must get.  Air circulation is a must.

[k4kyv]

The outboard audio amp I use for my receiver is an old 50's vintage 10-watt monaural hi-fi amplifier I picked off kerbside on trash day in Boston about 35 years ago.  It uses a pair of 6V6s in the output, and the rest of the tubes are a couple of 6SL7s, a 6SN7 and 5Y3 rectifier.  I  replaced the stock output transformer with a UTC LS series 20w output transformer.

It puts out good audio, but one thing I noticed was that the tubes ran awfully hot to the touch. Voltages and currents were all within the normal range according to the tube manuals, except for filament voltage, which was a fraction of a volt high. But the 6V6s would last only a year or so before they would test weak, and eventually I could tell that the output had decreased.  I went through about 3 sets of 6V6s before I  finally decided that something was killing the tubes, and that I was not just replacing worn-out tubes with other worn-out tubes.

I would often let the receiver and amplifier both run 24/7. I have several RCA "Iso-Tap" isolation transformers with tapped secondaries, designed for TV repair bench work, so I put one between the  receiver and audio amp, and the 120v line, and ran the line voltage down to 110 volts. That brought the filament voltage to something  like 6.02 volts IIRC. I started turning the power completely off over night and when I know the receiver won't be used for a while.

Now, the tubes are no longer searing hot to the touch, and it's been 2 or 3 years now, and I haven't had to replace the 6V6s. I also have noticed fewer tubes going bad in the receiver.  I now believe that old story about small receiving tubes lasting longer if they are run 24/7 is just that - an old wives' hammy hambones' tale.

I would say that the older tube type equipment rated at 105-125 volts was actually rated for 115 volts, and  the 105 and 125 volt figures reflect the extreme limits of the recommended voltage range.  That doesn't mean the equipment will perform as well or last as long if the voltage is maintained at either extreme.

That's why rebuilt car engines don't usually last as long as brand new ones.  All the parts in the rebuilt one may still be within manufacturer's tolerances, but many of those parts will be close to the edge of tolerance from normal wear, so it doesn't take as long for a substantial portion of the parts to wear down even further to a point beyond tolerance, than in the case of a new engine whose parts will average closer to nominal at the middle of the range, allowing a considerably longer time before expected failure.

[KD6VXI]

That's why rebuilt car engines don't usually last as long as brand new ones.  All the parts in the rebuilt one may still be within manufacturer's tolerances, but many of those parts will be close to the edge of tolerance from normal wear, so it doesn't take as long for a substantial portion of the parts to wear down even further to a point beyond tolerance, than in the case of a new engine whose parts will average closer to nominal at the middle of the range, allowing a considerably longer time before expected failure.

Which is exactly why I went with a 383 stroker when my original 350 Chebby went out.  Everything had to be new (except the distributor, which as you say was JUST within tolerance, and I gained about 18 horse by adding a new one).

I got 750K out of the OEM motor....  If I get 2/3 that out of this one, I'll be a happy camper!

--Shane

I got 750K out of the original engine...  If I get 2/3 that out of the stroker, I'll be happy!

[Opcom]

For whole-property regulation, I will use the General Electric Inductrol equipment. They are not connected to the mains yet, as I had planned to use them in the lab only and do it myself, but now want to let them take care of everything and need an electrician.

Inductrol is a contactless, stepless regulator using a stator buckboost winding and a rotor with a winding in series with the load. Two are used for 240V and regulate each side independently. The rotor is turned one way or the other by a motor to raise or lower the load voltage. In its 180 degree rotation, it can buck or boost as much as 20%. A controller senses load voltage and tells the motor which way to turn until the error is corrected. I can keep the entire place regulated regardless of any un-even loads. The regulation is 1%.
I assume GE still makes these, but their web page is horrible for finding anything.


The lab, which has the ham shack in it, is connected to the house through some 100FT of wire. Because of this, the lab A/C has an effect on line voltage to the sensitive radio gear and the test equipment. I do spot-regulate there, by rack bay or work station, with a Staco Energy Products voltage regulator.
These are a specially tapped Variac type autotransformer connected to a special power transformer with a high current low voltage secondary. That secondary is in series with the load.
As the autotransformer goes from above the tap to below it, the secondary voltage of the buckboost transformer diminished in amplitude, reverses phase, and increases. Because of the many wiper contacts on the autotransformer versus the range of voltage change, the regulation appears stepless. This is to say the variable autotransformer turns all the way around, for only a 20V change in output voltage to the load.
The ones I have are older rackmounted 6.5KVA 120V units and supply everything and pretty much just idle unles I run the leenyar or start working on a larger TX.
http://www.stacoenergy.com/pdf/brochures/Voltage%20Regulator%20Brochure.pdf

If all you require is to knock 10V off the line and the only concern is over-voltage-sensitive radio receivers and small TX and only need 20A or less, a 120V to 10VCT filament or 12VCT control transformer would be OK for bucking. The thing is switching it in and out. A large enough relay or contactor, or a set of them, so you can engage 0, 5, or 10 volts buck, and then a reversing contactor (dpdt switch) for the primary to allow boost. I've done that one before with the circuit below in my military truck, which used a generator set and it worked great.

[KM1H]

You cant argue with the physics involved Don   less voltage means less current means less heat. Anybody disagreeing with that probably voted for Whatshisname

My HRO-60 transformer at 111V and a 6V6 for the ballast runs so much cooler than at 124V. Same with the tubes.
 
Carl
KM1H

[Opcom]

Excellent use for a deceased 6V6. Does the turn on surge bother it at all?

Note to self, do not pitch out bad power tubes. Epoxy-pot in steel sleeve along with one of those uranium glass marbles, and sell on epay for a mere $900 with proper marketing pitch hailing atomic-vacuum-ballast technology. "Black Hole"(tm) brand. yep. as sideline, sell geiger counters so customers can tell the product is working up to snuff.

[KM1H]

The surge has no effect, in fact National wrote a Service Bulletin authorizing the 6V6 in all 4H4 equipped models. I even use one in the Clegg Zeus. Sell the 4H4's on Ebay to the purists. And yes, I only use the weak or leaky dogs

Speaking of leaky the 6V6 is prone to that and I suspect it is due to being run hard on both the B+ and filament. Just another reason to reduce both.

Carl