tube heater voltage, how much is too much?

[rdf]

Agreed...we all seem to providing solutions for a problem that shouldn't be happening in the first place...IE line voltage variations.

Most large utilities post their acceptable range of voltage variance online, you'll be surprised. For BC Hydro the acceptable voltage range at the service entrance is set by CSA Standard CAN3-C235-83 at between 110VAC and 125 VAC.
Yet more disconcerting aspects, the utility in my municipality no longer seems to provide sine wave power. Much closer to a clipped triangle appears every place it's been measured across the city.
Add to that transformer manufacturers who haven't retooled old and established designs in response changing voltages. I don't own a single Hammond power transformer that delivers close to 6.3VAC filament power at rated current. It's always (dangerously in my opinion) high.

 

[wa2ise]

Here's an even easier solution:

Take a filament transformer... anything with 5 amps secondary rating, or more.

Connect the primary across the voltage from the wall... with a wall cord.

Connect one lead of the secondary to one lead of the primary, and measure the voltage difference between the other secondary lead and the other primary lead. If the voltage is HIGHER than the wall voltage, REVERSE the secondary leads until the voltage is LOWER (and it should be by the voltage rating of the secondary of the transformer... i.e, if it's a 6.3 volt filament transformer, it should be lower by about 6.3 volts or so). Once you've done this, connect the second secondary lead to one side of an outlet socket, and the second primary lead to the other side of said outlet socket.

I do this slightly differently: I have the transformer's primary winding connected to the load, and then I connect one end of that winding and the load to the powerline neutral (white wire), and the powerline hot (black wire) I connect to one side of the 6V secondary winding, and the other end of the secondary connects to the "primary" winding and load. And of course the secondary winding must be phased to not buck the "primary". This creates an autoformer that has, on the input side, 6V + 117V AC windings, and the load sees just the 117V AC winding. Here you do not want 117V - 6V as seen by the incoming powerline. This way lets the transformer run cooler, and gives it extra margin before excessive powerline voltage would cause core saturation.

crude ASCII art diagram:
.................................../-----------load-------------------\
powerline--------eeeee--+-eeeeeeeeeeeeeeeeeee------- neutral
........................=======================

Where e's are windings, === are the lams, and ... are just spacers, as this web site ignores multiple spaces.

 

[randytsuch]

So, I ebayed a used 10a variac yesterday, should have it in a week or so, which works out since I am on vacation this week.

I may only do this as a temparary solution, with either a buck transformer or the step down balanced transformer as a permanent solution, have not decided yet.

Thanks again for all the help, and the ideas.

Randy

 

[shermanr]

rush2112

I have used a Variac with success. despite the claims that it affects the sound. Too high filament voltage shortens tube life while too low may cause distortion, a hissing sound and other not so friendly side effects. Let me know what you decide and I can draw-up a very simple and effective Balanced Power schematic and send to you.

Equitech is the leader in Balanced Power, but their products are $uperb....

www.equitech.com

Good luck,
Rich

 

[speakerfritz]

There are isolation transformers called isotaps that have options on them that result in lowering the voltage to your gear. You just have to check the power rating of the gear and make sure the isotap covers the wattage.

 

[kmaier]

As line voltage and sine-wave quality is an issue in most places, why not bite the bullet and get a CVS setup... they're not that cheap but maintain about 1% regulation, provide a clean sine-wave and will do more to isolate and protect your expensive gear than anything else beyond your own power company.

http://www.sola-hevi-duty.com/products/powerconditioning/cvs.htm#Specifications

A 500VA retails for about $900, but a pair of WE300B triodes is about the same. And they do come up on ebay from time to time for much less.

Regards, KM

 

[TonyTecson]

Hi,

you can series connect a 1 ohm, 5watt resistor for the 6SN7, and a 0.75 ohm, 5 watt resistor for the 300B and you should be safe....