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Dirty-South Blues Harp forum: wail on! >
Inquiry on step down transformer
Inquiry on step down transformer
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LittleJoeSamson
130 posts
Nov 21, 2009
12:51 PM
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I am wondering if any here know of a simple ( i.e., "cheap" ) solution.
Most older electronic equipment is set to run on 110 Volts AC, but today, the output at the wall is higher...120V where I am. This could damage expensive and many times hard to find components in vintage unite.
I know that I could pick up a variac ( and if an inexpensive one were available, I would go that way ), but really, being a variable transformer is superfluous. All I need is a step down from 120V to 110V, or a 90% reduction in voltage.
Does anyone have any suggestions?
Thanks, LJS
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Andrew
755 posts
Nov 21, 2009
2:30 PM
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Yes, I suggest you don't worry about it.
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Kinda hot in these rhinos!
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LittleJoeSamson
131 posts
Nov 21, 2009
7:17 PM
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Thanks for the words of wisdom, Andrew.
I take it your amps aren't worth much, or you don't give a hoot.
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Randy G. Blues
105 posts
Nov 22, 2009
10:56 AM
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Most electronics are designed to operate within a range of acceptable voltage input. 120 is only about 9% over 110, so if the 110v amp was designed to operate within +/-10% then it should be fine.
While I am not an electronics guy, I would be more worried about running a device at lower than rated voltage since the device would then be forced to draw more amperage.
Since you did not mention what amp it is or its design it's hard to say whether you should worry or not. If it has an input transformer then you are probably fine. If not, maybe it's time to add one...? Dropping voltage through a regulator circuit is not that difficult. You should be able to find plans for such a device that can be added in the amp's cabinet and even add a small voltmeter to monitor the output.
Check eBay for Variacs. They come in various output wattage so be sure to get one that will cover the amp you are using. A lot of my coffee-roasting buddies get them to control their home roasters.
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Tuckster
268 posts
Nov 22, 2009
5:14 PM
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LJS I'm not sure if that 10 volts is worth worrying about. To be sure,I think you'd want to measure plate voltage and see if it's in safe operating area for that tube's specs. I would think it could shorten tube life if doing no other harm. If the caps are of not a high enough voltage rating, it might take them out.A transformer seems like overkill and one more thing to lug along.It seems its been working well so far. Barring component aging,it should continue to keep giving you good service.
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Jim Rumbaugh
109 posts
Nov 22, 2009
6:36 PM
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From my electronics training in the 60's I also say, "don't worry about it". I would be surprised if it the lable saying 110 volts was an EXACT recomendation.
An intresting note on a similar subect. If I take a 12 volt power supply that powers some small apliance and measure the voltage, I'll typically find the voltage to be 14 to 16 volts (no load). Precision is not always a factor on these lables.
Granted, I am sure there will be someone that says any variation in original design can effect the performance, but I have not experienced it.
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LittleJoeSamson
134 posts
Nov 22, 2009
10:03 PM
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The main amp in question is almost 70 years old, and quite valuable. There's one just like it in "Cadillac Records", the first one Muddy Waters is hauling around.
I was advised by another musician that has about two dozen vintage amps to do this. He didn't say, "Don't worry about it".
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Andrew
758 posts
Nov 23, 2009
2:47 AM
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I understand your concern perfectly. And for peace of mind, if for nothing else, I'd say, OK, get a transformer if you want to, at least it can't harm.
But you must realise that you can't necessarily rely on your collector friend for objective advice!
Also, I'd ask you, are you familiar with the components in the amp, or are you assuming they'd be difficult to replace?
To put it another way, if you haven't yet started collecting spare parts, then you should begin now (and hoard as many as you can). But I'm guessing your collector friend will already have told you that.
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Kinda hot in these rhinos!
Last Edited by on Nov 23, 2009 2:50 AM
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congaron
294 posts
Nov 23, 2009
11:44 AM
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Have you asked an electronics repair technician who works with tube amps this question? If not, I will ask mine via e-mail. My first inclination is not to worry about it. Here's why:
Voltage is the available "push" for current. Current draw is determined by the resistance of the load. Having a little extra voltage doesn't force more current through the circuitry, within reason...not talking about doubling here...just a few percent. If you have a battery charger for your car, you'll find a trickle charge setting that only "pushes" hard enough ( around 14 v) for the battery to draw around 2 amps. When you select the 40 amp setting, you'll find the measured voltage to be around 18 volts, allowing the battery to "draw" up to 40 amps if the charge state of the battery (it's internal resistance, if you will)requires it. As the state of the battery improves, the charge rate will reduce to 10 amps after awhile and the charger will shut off or you need to shut it off to avoid boiling out the water. This all varies with the amount of charge already in the battery. It is somewhat inexact, but i will ask my friend Jim at little dawg amps if you don't have a guy.
Last Edited by on Nov 23, 2009 11:51 AM
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congaron
295 posts
Nov 23, 2009
11:50 AM
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Another example..My electret mic experiments really only "require" 1.5 volts. I run them on 9v batteries because they last longer and this voltage is within the range specified in the data sheet. Here' we're talking about a huge percentage of acceptable increase without damage.
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Tuckster
274 posts
Nov 23, 2009
1:46 PM
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70 y.o.?!! If it's a valuable piece of vintage gear,you'd be better off spending your $$'s on a good technician specializing in vintage amps.Pay him to give it a thorough going over. Filter caps dry out and don't last forever. A shorted cap can take out both transformers. You don't want that to happen! At that age,I'd worry about ageing components more than 120 volts.
Last Edited by on Nov 23, 2009 1:50 PM
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LittleJoeSamson
135 posts
Nov 23, 2009
3:41 PM
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@ Tuckster --- Oh yeah, I've done all that. First thing I did when I acquired this museum piece is to have my tech check everything out. He replaced several filter caps with Mallory's, and the pair of 6SQ7's with metal Mullards.
This guy is not only an amp wizard, but is fastidious. I would just give him old stuff I couldn't use, and then when I would have him do work for me he would invite me down for a BBQ and say to just bring a twelve pack.
His wife was quite the looker and he was used to guys hitting on her, but I always showed due respect...to both of them. When my friend would go up to play bass or git, I was one that he would ask to sit with the wife and even dance with.
I've babied the amp since then, but there are special occasions where I want that sound.
I have a special project coming up...recording many of my originals, and I want that raw Chicago sound: Big Walter/Jerry McCain gritty, for certain numbers.
Because of this, I have been experimenting with the pair of drive tubes. The 6V6GT's that were in it were 1952 Magnovox. At low volume, everything was fine; but to get that fuzzy distortion at higher volume, it sounded kind of mushy.
I pulled them and took them to my new tech.
( I miss my old one, but he lives 3,000 miles from me now ).
Sure enough, there was an imbalance. One was like new, the other was barely usable ( although no shorts or leaks! )
I picked up a quad of CBS greyglass from 1953, and picked the best sounding pair.
My new tech GAVE me a pair of Raytheon for DELCO (1964) that simply scream....rated the highest distortion ( 1.57 ) in Vacuum Tube Valley. These were most likely among the last audio tubes designed for automtive application.
This is another reason I want to tone it down with a variac.
BTW, I also ran this by my new tech, and he was supportive of the idea...and he even said he would give me a variac if he had one ( so no ulterior/financial motive ).
Quite naturally, my primary consideration is to not damage my vintage amp.
Secondarily, is the sound.
I am discovering that by voicing my recent addition, the Blackheart Handsome Devil BH-15H; that the tone, sound, and presence is coming darn close to my specs.
My query was if there were a simple solution for a step-down transformer...and I have found out much more!
Many thanks to all... LJS ( New stage name is "Joey Five & Dimes" )
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Preston
550 posts
Nov 24, 2009
6:04 AM
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As an electrician, I have to deal with this on a regular basis.
Alot of stuff still comes from the factory rated at 110volts, even though 120volts is the standard rating from the utility companies.
There is also something called voltage drop. The farther away you are from the power source, the more volts you drop off if your wire is not oversized to compensate. You may put a meter in the receptacle and it reads 120 volts, but as soon as you plug the amp in and turn it on the amperage draw may drop the voltage down a few volts, depending on the circumstances of the install. I'm guessing most of the receptacles you plug into at a show has not been sized to accomodate voltage drop, but rather sized to accomodate the owners check book.
Further more, the actual voltage produced by the power company varies. If you are close to a sub station you may be running hot and have around 125volts. If you are the last house down an old forgotten road leading out of town you may only have around 115 volts.
So, yeah, don't worry about it!
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