Effect of high mains voltage?

rntlee · 20th January 2012, 07:28 PM

Hi,
I have recently received an MS-20L and it appears to be built for a mains supply of 115 VAC. I've measured my mains voltage at 126 VAC, so I checked the heater voltage at the socket and it's at 6.9 VAC. I searched through some old threads and found this graph:

Which shows that at 10% higher than rated heater voltage, tube life decreases by 10%...so I'm debating whether remediation is worth the effort...

I can get a variac for $100, but is that the way to go?

Alexontherocks · 20th January 2012, 07:45 PM

rather than getting a variac which I would rather use for developing projects try to source a custom (or prebuilt) transformer which will give you the desired voltage drop for 115VAC use.
An isolation transformer might be what you are looking for. It costs a fraction of an ordinary transformer (isolated windings) and will still support large power demands.

DF96 · 20th January 2012, 07:52 PM

A 10% change on a number (valve life) you only know to about one significant figure (at most) is not really a change at all. If you are worried either use a resistor to drop the heater voltage a bit, or a buck transformer on the mains supply.

Yvesm · 20th January 2012, 07:56 PM

Interesting to see that under voltage is much more objectionable . . .

DF96 · 20th January 2012, 08:14 PM

A cool cathode has less protection from ion bombardment.

aardvarkash10 · 20th January 2012, 08:55 PM

is your line voltage measurement accurate? Loaded or unloaded? It may be that you don't have a problem at all...

FullRangeMan · 20th January 2012, 09:08 PM

Quote:

Originally Posted by rntlee

Hi,
I have recently received an MS-20L and it appears to be built for a mains supply of 115 VAC. I've measured my mains voltage at 126 VAC, so I checked the heater voltage at the socket and it's at 6.9 VAC. I searched through some old threads and found this graph:

Which shows that at 10% higher than rated heater voltage, tube life decreases by 10%...so I'm debating whether remediation is worth the effort...

I can get a variac for $100, but is that the way to go?

I will agree with a previous poster, I do not like Variacs or external transformers, cause the new avaliable power to the amp, will be the only the max Variac power, which is smaller than a electric plant or building big transformer.
I would prefer re-winding the amp transformer to the right tension of the house.
Good luck

simon7000 · 20th January 2012, 09:15 PM

Try a 12 volt transformer in series with the line to buck the voltage. Place the buck transformer primary after the bucking secondary and you should be dead on. A 4 to 6 amp unit should do fine.

Speedskater · 20th January 2012, 11:11 PM

More on buck/boost transformers:

Bucking Xfmrs

rntlee · 20th January 2012, 11:59 PM

Would something like this work?

Acme T-1-81048 Buck Boost Transformer AT1467 - 120x240 Primary 12/24 Secondary - 0.1 kVA - 60Hz - 1 Phase - NEMA 3R Encapsulated

20th January 2012, 07:28 PM	#1
rntlee diyAudio Member Join Date: Jan 2012	Effect of high mains voltage? Hi, I have recently received an MS-20L and it appears to be built for a mains supply of 115 VAC. I've measured my mains voltage at 126 VAC, so I checked the heater voltage at the socket and it's at 6.9 VAC. I searched through some old threads and found this graph: Which shows that at 10% higher than rated heater voltage, tube life decreases by 10%...so I'm debating whether remediation is worth the effort... I can get a variac for $100, but is that the way to go?

20th January 2012, 08:55 PM	#6
aardvarkash10 diyAudio Member Join Date: Mar 2007 Location: Auckland, NZ	is your line voltage measurement accurate? Loaded or unloaded? It may be that you don't have a problem at all... __________________ Yes, conservatism thrives on low intelligence and poor information. But the liberals in politics... continue to back off, yielding to the supremacy of the stupid. It's turkeys all the way down. - George Monbiot, guardian.co.uk, 6 Feb 2012

20th January 2012, 11:11 PM	#9
Speedskater diyAudio Member Join Date: Sep 2002 Location: Lakewood, Ohio	More on buck/boost transformers: Bucking Xfmrs __________________ Kevin

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
In-depth analysis of effect of high-quality interconnects	halfgaar	Analog Line Level	7	9th January 2012 05:49 PM
What effect does a cabinet have when using a high-pass filter?	lazyfly	Full Range	1	22nd May 2010 03:49 PM
Mains hum on a guitar effect unit! Help (circuit enclosed)	HankMcSpank	Solid State	10	18th March 2009 11:44 AM
Effect of high efficiency speakers	mxv146	Multi-Way	9	9th April 2005 11:34 AM
does plate current/voltage effect tube sound????	benny	Tubes / Valves	10	7th July 2004 01:18 PM

20th January 2012, 07:45 PM	#2
Alexontherocks diyAudio Member Join Date: Jul 2009	rather than getting a variac which I would rather use for developing projects try to source a custom (or prebuilt) transformer which will give you the desired voltage drop for 115VAC use. An isolation transformer might be what you are looking for. It costs a fraction of an ordinary transformer (isolated windings) and will still support large power demands.

20th January 2012, 07:52 PM	#3
DF96 diyAudio Member Join Date: May 2007	A 10% change on a number (valve life) you only know to about one significant figure (at most) is not really a change at all. If you are worried either use a resistor to drop the heater voltage a bit, or a buck transformer on the mains supply.

20th January 2012, 07:56 PM	#4
Yvesm diyAudio Member Join Date: Jul 2004 Location: Ardeche	Interesting to see that under voltage is much more objectionable . . .

20th January 2012, 08:14 PM	#5
DF96 diyAudio Member Join Date: May 2007	A cool cathode has less protection from ion bombardment.

20th January 2012, 09:15 PM	#8
simon7000 diyAudio Member Join Date: Nov 2008 Location: Oakmont PA	Try a 12 volt transformer in series with the line to buck the voltage. Place the buck transformer primary after the bucking secondary and you should be dead on. A 4 to 6 amp unit should do fine.

20th January 2012, 11:59 PM	#10
rntlee diyAudio Member Join Date: Jan 2012	Would something like this work? Acme T-1-81048 Buck Boost Transformer AT1467 - 120x240 Primary 12/24 Secondary - 0.1 kVA - 60Hz - 1 Phase - NEMA 3R Encapsulated

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read