Line voltage too high?

[DavGoodlin]

Mine is 123-125 VAC most of the time, even on hot days, since the utility replaced the Truman-Era pole transformer. It was 112-115 and everything was happy, but had to upgrade from a 60 fused service to 200 amp main circuit breaker panel and meter to install central A/C.

What's worse is that this is acceptable per the utility and rules of service because it is within 5% of 120. So, even if there was a higher primary winding tap on the pole trans, which there isn't, the utility would not adjust it anyway.

Obviously, most of vintage electronics is designed for 117 volts maximum. Some of the most concern are 1930-40s radios and tube TVs with power transformers. And, unlike some later tube color sets, most lack a hi-line tap on the transformer.

My initial approach was to install an inrush limiter (thermistor) GE CL-90 is rated 2 amps and the CL-70 is 4 amps for those big color TVs. Unfortunately, these do not drop more than a volt after heating up.

Ill assume a step-down trans or variac for each set is not practical or cheap. What is your tech-seasoned opinion on the following proposed solutions?

1. A "buck", auto transformer using a common 120-12.6v filament transformer, assuming the secondary is rated for the same current as the intended load. Less heat but....

2. Series resistors. for example, to drop 10 volts at 2 amps load, a 5 ohm 20 watt resistor is needed. Or more practically, four 2.7 ohm 10 watt resistors in series/parallel. Lower cost but...

[old_coot88]

Back in the day I used toaster elements for motor speed control. Easy to tap with a coupla alligator clip leads. Kinda hillbilly way of doing it, but worked fine. Should work as well for line voltage droppage for TVs. Just cannibalize an old toaster from Goodwill.

[Tubejunke]

Recently I have noted that two of my three Zenith Transoceanic radios don't like line voltage (I think 120V). However, if I use my variable supply that is plugged into an isolation transformer they play wonderfully. The third, which is the later and final tube design (model 600) and employs a current limiting tube works fine off the line. I'm not really sure what is going on with this. It's not a real bother as I have heard that it is best to run these radios either on DC or as I mentioned on a reduced voltage due to the delicate 1.4V tube filaments. They are very easy to open and one of the tubes is pretty pricey.

[roundscreen]

Series resistors are the safest way to do it. I installed a 5 ohm 25w resistor in the CTC 9 and it works fine. Fell a sleep with the set on many times and she is still working.

[ChrisW6ATV]

The resistors are probably cheaper, but I am going to build a bucking-transformer box with this transformer:

http://www.jameco.com/webapp/wcs/sto...0001_102121_-1

In your case, I would go down the whole 12 volts.

[DavGoodlin]

This seems to be an issue for most of us and even 120 is too high IMHO.

It used to be if you were in an older neighborhood, with many other homes sharing a transformer, you were always running less than 120.

Thanks for the feedback!

[maxhifi]

I have a "little bear" tube phono preamp I bought on eBay, the primary of the power transformer is rated at 110V like most mainland China stuff. On our 121V it saturated a bit and got hot... I used a 10W 100 ohm ceramic resistor on a terminal strip in series with the primary and its happy now, the transforner gets about 109V which is a lot closer to 110 than 121 is . I wouldn't use a reaistor in series with something with varying current draw, it could have an impact on performance, but something with all class A amplification like an aa5 radio it just makes sense.

I wonder how much a TV varies in current draw during all possible conditions of operation. I would guess not too much, the dominant factor is the horizontal output cathode current which is fairly constant and then the tube heater draw. I would think resistors would be the best bet.

I don't really like adding transformers if it can be avoided - for one thing if the core saturates it can add some buzz to the audio, and if not placed properly can inductively couple 60Hz to whatever is near. I guess a big 15A bucking transforner which is used to power all the vintage electronics in a room may make sense, but I would definitely say the resistor option is preferred where it's practical.

[TUD1]

Interesting. My problem is just the opposite. I have lower line voltage than most people - never gets above 120. I used my space heater last night, and it got down to 107. The CTC-25 did -not- like that. Lots of picture shrinkage. It is currently on the high line voltage tap.

[teevee]

Using a bucking transformer is the way to go. Select the secondary voltage and current for the amount you want to drop, and the load current. Little heat, stable output.

[wa2ise]

I put the secondary in series with the primary, so the transformer will run a little cooler, and allows a higher input voltage without the transformer core saturating.

When putting it together, be prepared to reverse the secondary wire connections. Test the output to see if the voltage in fact is lower. If higher, reverse the secondary connections, but not the primary.

[rca2000]

Go and grab THIS..

It WILL keep your line voltage to about 117 or so..EVEN IF the input reaches about 130 or MORE.

it is rated at 350W...BUT a few members hav ethem and have used them on 5'S and 7's..with NO ill effects..

Know ONE thing...it is NOT isolated though...if that matters. but for line cotrol...it will NOT.

http://www.ebay.com/itm/SOLA-ColorVo...IAAOSwFMZWrP9Z

[Electronic M]

Originally Posted by rca2000

Go and grab THIS..

It WILL keep your line voltage to about 117 or so..EVEN IF the input reaches about 130 or MORE.

it is rated at 350W...BUT a few members hav ethem and have used them on 5'S and 7's..with NO ill effects..

Know ONE thing...it is NOT isolated though...if that matters. but for line cotrol...it will NOT.

http://www.ebay.com/itm/SOLA-ColorVo...IAAOSwFMZWrP9Z

There are isolated line voltage VRTs too. I use three on m main sets, though I use them to deal with low line voltage and annoying spikes, but they will work with high line too.

I've got 2 250VA (W) units each serving serving a 300-340W set and a 500VA unit serving a 500W set. They work very nice ( but they do get kinda hot especially after 3-5 hours on) and even if something like a fridge on the same line kicks on there is no blooming.

[dieseljeep]

Originally Posted by TUD1

Interesting. My problem is just the opposite. I have lower line voltage than most people - never gets above 120. I used my space heater last night, and it got down to 107. The CTC-25 did -not- like that. Lots of picture shrinkage. It is currently on the high line voltage tap.

That's a lot of voltage drop, for a 1500watt load! Three volts, maybe, but not thirteen!
It depends on the age of the home and the wiring methods used. It could be bad connections in junction boxes, etc.
In newer homes, it could be "backstabbed" connections used on the receptacles. When using a high current device, portable heater or window air conditioner, it's best to check to see if the plug or receptacle is running hot.
Maybe best, to get an electrician involved.

[rca2000]

A VRT will work for BOTH situations !!--HIGH V and LOW V...

[DavGoodlin]

Originally Posted by dieseljeep

That's a lot of voltage drop, for a 1500watt load! Three volts, maybe, but not thirteen!
It depends on the age of the home and the wiring methods used. It could be bad connections in junction boxes, etc.
In newer homes, it could be "backstabbed" connections used on the receptacles. When using a high current device, portable heater or window air conditioner, it's best to check to see if the plug or receptacle is running hot.
Maybe best, to get an electrician involved.

Yep, those lousy push-in or e-z wire receptacles suck. UL made a HUUUGE blunder listing those
Pull 'em out and pigtail thru-wiring if your box is big enough or replace with back-wired/screw-tightened receptacles - do not use anything that cost less than $1.50