Low Voltage

I have started to check my line voltage three times a day to give me some perceptive on fluctuations in degrees regarding the safety and usage of tubes burning unnecessarily quicker in my m125's.
This mornings reading was low....107.9

Any thoughts on how this reading would affect tubes and there performance.
I would think that this reading (which I checked in more than one outlet) and after biasing in triode mode .600 would put a strain on the output and driver tubes while also causing a high heat issue with the transformers potentially over time damageing both...power & output.

Thanks,
Frank

I'm not an expert but that seems really low. First thing I'd check is the battery in your meter.

In these amps B+ bias and filaments are all unregulated and follows each other. Thus when
mains is low both B+ and bias voltages will be reduced, so will the current through the tubes ( the measured bias). In effect keeping performance up.
Adjusting bias should be done at nominal ac ( 120V ?) and one should not readjust every time
AC changes. It should not bee needed , the only thing one could / should do is check that
measured bias is approximately equal on both tubes in each channel.
If bias changes much, the output tubes are faulty and should be replaced.

Line voltage of 107 is uncommonly low. You might consider requesting your electric company check the transformer on the pole that serves you. My own experience with this is that the provider actually appreciates the opportunity to improve your service. Without your input, they have no apparatus in place to monitor the voltages in every neighborhood.
As far as your concerns about your amps' bias, my method, which is based not on expertise but on pure logic, is to bias your outputs when the line voltage is at its maximum (in my case the max is 118VAC, for example). Bias on my ST-120 can vary, but not by any great value. It may drop down to .50 at times (I use the standard of .55 recommended by Bob) but I know of no reason why a slightly LOW reading would cause any damage to anything. In short, I believe that once set under the greatest possible stress conditions, there should be no need to worry. Someone correct me if my logic is flawed, please.
I'm assuming that you are running KT-120s, since you are jacking up the bias to .60. Word has it that, even at this level, the tubes are not breathing heavily. What may be stressing is the rectifier. And I'm guessing that you use Weber SS units. Watch your temps on these. They are apparently fairly easy to melt down. But they are inexpensive. So keep an extra pair just in case (???).

Thanks everyone.
The battery in the meter is new.
I checked at noon and the voltage spiked up to 118.9 a constant level for over an hour.

Kent I am using the KT88's biasing at .600 although there are variances in that number. You are correct about the Rectifier. Weber wz68

Don't hesitate -- cal your electric provider right away. I don't think a 10% variability in your line voltage is acceptable. I would be shocked (!!!) if they didn't agree with me. More than likely, they aren't even aware of the fluctuation. Good luck.

That line level is dangerously low ... browning out your electronics can be worse than running them at higher levels. +1 on the WTF call to the electric company.

That said, you'd be better served investing in a Kill-A-Watt meter to monitor your AC levels. That can give you min/max and average over time. Just plug it into any available socket. That's also handy for finding out whether the problem is with the service, or just a particular circuit.

You HAVE tried checking other circuits? You'd be surprised what all can happen to what was once a well balanced power panel over time. This Old Hovel has been added on and recycled several times and it's fun pulling a fuse and finding scattered bits of the house and yard going dark. I got around that by running a dedicated circuit for just the stereo.

PS ... remember this one?



https://www.youtube.com/watch?v=QBDrRl7d5ZA

Just for the record I had tried three other outlast in the house besides my dedicated room and they all had the same LOW reading.
Having said that I have been moderating the line voltage for a few days now and will for another four-five but I believe the readings that morning was an isolated incident.
The afternoons and evenings have been normal readings even the day of the morning I had a reading of 107.9.
That said I will take Kent advice and call PECO my utility provider and ask a few questions.

Having been down this road, I learned that utilities are required by law and regulation to supply voltage at 120VAC plus or minus 10 percent. Which means between 108 and a quite scary 132VAC. Low volts are nice on light bulbs but murder on motorized electric appliances because of the extra amps they must draw.
You might back down your bias a bit. .6VDC seems a little hot for KT-88s. Try going down to .5 and see if you can hear any degradation -- betcha can't, and your tubes will thank you for it.

Just fyi, Bob's instructions call for .600v in an M125 with KT88's, but a little less won't hurt.

audiobill wrote:Just fyi, Bob's instructions call for .600v in an M125 with KT88's, but a little less won't hurt.

Quite so. But my advice from personal experience is to start at .45 and work your way up.

Once I got to 45, it was all down!

audiobill wrote:Once I got to 45, it was all down!

To like 33 and 3/d? Or were you shooting for 16 and 78ths?

it's probably been 40 years since I've lived in a house that was older than I was, but variations in the AC power greater than +/- 5% are totally unacceptable.
I'd invest $300-600 in a AC power conditioner that automatically keeps the voltage within 5%, that's a super cheap investment for your stereo system.

this is the least expensive power line conditioner I've found that will maintain the voltage within +/- 5vac of 120vac
Panamax M5400 $441
http://www.amazon.com/gp/product/B000SXWGAG

tubes4hifi wrote:this is the least expensive power line conditioner I've found that will maintain the voltage within +/- 5vac of 120vac
Panamax M5400   $441
http://www.amazon.com/gp/product/B000SXWGAG

That you for your input. As mentioned I have the Furman Elite which is more than adequate to handle the job. The unit cost was $600.00 a few years back.
I have been monitoring the voltage in my house this entire week, which by the way, five years ago I had a new circuit breaker box and some additional in house wiring added. At the time I asked for a system check to assure me that everything was up to date and within code.
Getting back to the monitoring, my voltage levels everyday, three times a day have been normal...between 116.9-119.5.
While I have not called PECO about the sudden decreased line voltage a few days ago I was talking to a PECO worker some eight blocks from my location working on lines due to new construction of a new WAWA. I was told they had on and off moved transformers in the area due to the extension and moving new lines for WAWA. I mention to him about the decline in voltage in my area not to far away and he said it was possible but not likely.
Despite his answer I have found no unacceptable readings since that day.
Coincidence?

Tech support at the local power company ...

PECO!

WAWA!!



They gotta work on their acronyms ...