High AC line voltage solutions

Variac, posted on March 23, 2015 at 10:49:30
richardl Audiophile Posts: 3555 Joined: September 5, 2002	It will lower the voltage. It is an expensive solution for separates though.

RE: Variac, posted on March 23, 2015 at 10:56:42
lugnut1 Audiophile Posts: 132 Location: Austin,TX Joined: September 24, 2011	Which solutions mess up the AC waveform least?

RE: High AC line voltage solutions, posted on March 23, 2015 at 11:03:46
DAK Audiophile Posts: 2712 Location: PACIFIC Joined: August 8, 2010	You can install some current limiters on the AC input, one per each leg. It should knock off 3 or 4 volts maybe more if you install the higher resistance ones. regards, Dak

RE: High AC line voltage solutions, posted on March 23, 2015 at 11:10:50
DAK Audiophile Posts: 2712 Location: PACIFIC Joined: August 8, 2010	Also a line conditioner, which usually set the voltage at 117v. They are sometimes noisy, and seem to limit current delivery. The expensive ones meant for audio probably are better than the ones for computers.

RE: High AC line voltage solutions, posted on March 23, 2015 at 12:32:44

Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000

Properly designed equipment intended for use in North America will run with the AC mains anywhere between 105 and 125 volts. That's been the standard for a VERY long time. Average mains voltages are higher in today's environment.

Problems can occur when the mains get above 125 V. Unfortunately, the mains frequently do get above 125 V., these days, during off peak usage hours. Let's say the power companies are not as vigilant as they should be. ;>)

Adding a "6" VAC transformer wired in the "buck" configuration is a good way to bring operating point voltages down, in older gear. Do you have the space needed? AnTek has some inexpensive toroids that can get the job done.

Eli D.

AnTek

+1 Buck transformer (nt), posted on March 23, 2015 at 13:30:03
gusser Audiophile Posts: 3649 Location: So. California Joined: September 6, 2006	q

RE: What makes you think you need a solution?, posted on March 23, 2015 at 16:18:57
Russ57 Audiophile Posts: 3754 Location: South Florida Joined: November 16, 2001	You are talking around 5.86% difference. Chances are your tubes, resistors, capacitors, etc. (all taken together) don't have a tighter tolerance (not to mention your power provider). If you are experiencing a problem please state what it is. Do include brand/model# of equipment and maybe we can help. To assume you must address this could lead to a fix that is worse than doing nothing.

RE: High AC line voltage solutions, posted on March 23, 2015 at 19:47:20
Tre' Industry Professional Posts: 17303 Location: So. Cal. Joined: February 9, 2002	"Adding a "6" VAC transformer wired in the "buck" configuration is a good way to bring operating point voltages down, in older gear." Also, a 12 VAC transformer works well in modern cheap Chinese gear with 110vac primaries. Tre' Have Fun and Enjoy the Music "Still Working the Problem"

RE: What makes you think you need a solution?, posted on March 23, 2015 at 20:25:25
lugnut1 Audiophile Posts: 132 Location: Austin,TX Joined: September 24, 2011	Filament runs high at 6.7-6.8 and B+ is about 25v high on a 400v rail.

sorry, terrible advice, posted on March 23, 2015 at 22:46:24
unclestu Dealer Posts: 5851 Joined: April 13, 2010	Transformers are voltage multipliers. A 5 volt line difference can translate to 25 + at B+. Caps fail, bias points shift, etc. ,etc. If using a tube rectifier easiest way use a less efficient tube: say 5ar4 to 5r4....

Solution?, posted on March 24, 2015 at 03:27:20

Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005

You don't need a solution IMO (and others here). I'd be shocked if anything is under rated to the extent that it would pose a problem, caps etc.

As for heaters, an inrush current limiter will drop the few tenths of a volt you need and limit current on startup as an added advantage.

Seriously, save your money, high voltage is generally your friend in tube gear unless the design is absolutely on the limit, which I doubt.

Naz

RE: High AC line voltage solutions, posted on March 24, 2015 at 06:49:01

FenderLover

This is why it is better to use higher voltage rated caps in the amp, if possible. Higher rated than the OEM ones. Like 500+ VDC rated main filter caps. 100VDC rated caps in the bias supply. 50-100VDC rated cathode-bypass caps. I like Mills or Ohmite WW resistors in the power rail. 10 and 12-watt ones. 5-watt in screen grid position.

Coupling caps of 600VDC rating and disc caps at or above 1KV.

I don't know of any consumer grade step-down tranny that doesn't color the tone of the amp. Maybe, there are industrial grade ones that may work well. These can be big house warmers and can use a lot of electricity.

I've had good luck just upgrading the components of vintage amps. Seems to make them stable with the higher wall voltages.

Filament Failure!, posted on March 24, 2015 at 10:08:42
gusser Audiophile Posts: 3649 Location: So. California Joined: September 6, 2006	I lost three KT88's over a year due to 6.6-6.8v filaments. Filament burnout was virtually unheard of in the old days but the new Russian and Chinese tubes seem very critical about filament voltage. What i did was to bring out the filament transformer primary to a separate AC connector ad used a Sola transformer to feed it.

RE: Filament Failure!, posted on March 24, 2015 at 10:14:39
vinnie2 Audiophile Posts: 4481 Location: North Carolina Joined: September 28, 2013	If that is happening I would use a different brand of tube. That's less than 10% over and there is no way they should burn out from that.

RE: Filament Failure!, posted on March 24, 2015 at 10:42:00

DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010

If I test the filament voltages and find them above 6.5v I install 2 watt metal oxide dropping resistors to bring the voltage down. I found that about .22 ohm to .33 ohm in each line will bring the voltage from 6.5 to about 6.1 with the .33 ohm resistors. Works great. cheers, Dak
PS, this was for a SE amp running 2 7591 and 1 12ax7. For an amp running higher filament currents you may need to use higher wattage dropping resistors.

+1 Buck transformer, posted on March 24, 2015 at 13:55:20
wheezer Audiophile Posts: 4309 Joined: January 24, 2001	Been doing it for many years.

Thta's no longer a problem!, posted on March 24, 2015 at 14:27:20
gusser Audiophile Posts: 3649 Location: So. California Joined: September 6, 2006	Svelanta (sp?) is gone AFAIK. I am currently running Gold Lions. But that experience made me gun shy about anything over 6.3v.

And yet ..., posted on March 24, 2015 at 15:28:58

Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005

at the opposite end of the scale I once tested a 845 filament (on an otherwise dud tube) to destruction. 50V on a 10V filament for an hour did not break it!

I have amps rated at 220V-230V AC input running various tubes with my mains varying from 230-260V and have never had a single filament failure. Admittedly, these days I always use inrush current limiters.

FWIW, I've run Svetlana KT88 filaments happily at 6.8V.

Naz

RE: And yet ..., posted on March 25, 2015 at 00:38:23

DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010

While I admire your audacity in running your tubes under such challenging conditions, the tube manufacturers did stringent research into filament voltage and tube life and the results are not good once you move past the design center the lifespan starts taking a steadily steepening nosedive. Unless, one has deep pockets for buying tubes, keeping the filament voltage at whatever the design center is should be an important issue. cheers, Dak

I've done lot's of things to test the limits ..., posted on March 25, 2015 at 03:15:43

Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005

that's just me. Note that I said I run inrush current limiters these days and have done for years. The few tenths of a volt drop under normal operating conditions keeps all of my filaments well within spec even under elevated mains voltage conditions.

So, to clarify my response to the initial poster's question I don't think anything needs to be done to the rest of the amp to cater for slightly higher mains voltage but I would still add a few cheap inrush current limiters to the filaments.

I would of course check the ratings of caps and the like but I'd be surprised if anything needed to be done in that respect.

Naz

RE: High AC line voltage solutions, posted on March 25, 2015 at 07:28:19
hifipaul Audiophile Posts: 735 Location: NY Joined: December 22, 2008	The simple cheap and easy way to reduce your voltages is to place resistors in series with the primaries (120v) of your power xfmr. 20W in the range of 2-15ohms (trial and error) will do it. There are downsides to this too. But it works.

RE: I've done lot's of things to test the limits ..., posted on March 25, 2015 at 12:58:06
DAK Audiophile Posts: 2712 Location: PACIFIC Joined: August 8, 2010	Hey Naz, if you check in my first post, that was primary recommendation. I found that you can knock the primary voltage back 3 to 5 volts depending on the CL used. Dak

RE: High AC line voltage solutions, posted on March 27, 2015 at 06:00:33

TimeConstant

The solution is quite straightforward and should not cost more than $150-200 in parts plus some metalwork.

Implement the use of a 1KVA Toroidal Step-down transformer designed with a ratio very close to 1:1 but slightly less on the secondary than on the primary.

This helps shave off the extra pesky 3-5 volts AC some vintage amps just don't work well with.

An additional benefit is that you can create the solution with an inrush current limiter CL-70 for a soft start, a Slo-Blo 4 amps fuse on the primary so you operate the transformer safely at 50% rating.

On the secondary you can wire the unit as Balanced Power feed so each leg on the AC receptacle will have 60 Volts AC and produce

Vsec = 60V-(-60v)= 120VAC, the same three wire configuration as a standard utility U.S. Mains connection, except at half the voltage.

If you need a schematic and part list, let me know.

RE: High AC line voltage solutions, posted on March 27, 2015 at 11:34:51
TimeConstant	Yeah this works but they sure can warm up!

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High AC line voltage solutions

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