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    Transformer to Reduce Line Voltage for Amp

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    Kramer

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    Transformer to Reduce Line Voltage for Amp

    Post by Kramer on Sun Mar 04, 2018 5:45 pm

    I recently tested my incoming line voltage in my outlets having ignored this until I had a issue with a output tube. It's shifting between 123-124 constantly which I understand is high as well. After looking into the options I found this product.

    https://www.amprx.net/store/p29/2018_Brownbox.html

    The price is high compared to other options but American made. I read quite a few posts of people using Chinese variacs and not them not lasting more than a year. I would rather spend a little more and have something that will go the extra miles and not need to constantly worry about possibly damaging the amp.

    Another option is to build a buck using a transformer and that would by far be the cheapest option but would be more difficult to adjust should I move in the future and have a different voltage altogether.

    Any opinions on the best route to reduce my line voltage reliably.
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    Bob Latino
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    Re: Transformer to Reduce Line Voltage for Amp

    Post by Bob Latino on Sun Mar 04, 2018 5:51 pm

    Kramer wrote:

    Any opinions on the best route to reduce my line voltage reliably.

    Check out the relatively inexpensive variacs from Circuit Specialists at the link below

    Variacs at Circuit Specialists

    The 5 amp one is good for any ST-70 amp. It also works well for the VTA ST-120. The 20 amp will run 2 X VTA M-125 amps.

    Bob
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    PeterCapo

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by PeterCapo on Sun Mar 04, 2018 6:15 pm

    An NTC thermistor rated accordingly and soldered in series with the power transformer primary winding will also work and is very inexpensive.
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    Dave_in_Va

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by Dave_in_Va on Sun Mar 04, 2018 6:32 pm

    I built this...

    https://robrobinette.com/5e3_Modifications.htm#Bucking_Transformer

    I built a simpler version of the "simple" version. I figured I didn't need a light and I didn't need the 12% reduction (I don't need to run anything at 108 volts).

    Really inexpensive. I think I had to spend about $35 but I had to buy everything including a project box. I think if you have some parts laying around you could get by with just buying the transformer.
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    Kramer

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by Kramer on Sun Mar 04, 2018 6:59 pm

    Dave_in_Va wrote:I built this...

    https://robrobinette.com/5e3_Modifications.htm#Bucking_Transformer

    I built a simpler version of the "simple" version. I figured I didn't need a light and I didn't need the 12% reduction (I don't need to run anything at 108 volts).

    Really inexpensive. I think I had to spend about $35 but I had to buy everything including a project box. I think if you have some parts laying around you could get by with just buying the transformer.

    Awesome, this looks like a great option. Thanks for the link.
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    sKiZo

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by sKiZo on Mon Mar 05, 2018 12:33 am

    My lil bucker cost nothing, as I found everything I needed in the parts bins ...



    Lot of folk use a power strip to start as they already have a power switch, output socket, and fuse. Make sure whatever transformer you use can handle the load.

    wildiowa

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by wildiowa on Mon Mar 05, 2018 10:52 am

    This topic comes up every few weeks. Many techies assemble a simple bucker. Others, like me, get a Variac, set it with a VOM for accuracy (don't trust device readouts) and forget it. Yes your voltage will vary slightly day to day and float with your input voltage, but the goal is to knock it down from the 125 range to somewhere under 120. I like 118. Don't be concerned with the Chinese units Bob endorses their use just check the actual output to be accurate. I blew my Cit II twice then got the Variac...no problems since.
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    deepee99

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by deepee99 on Mon Mar 05, 2018 12:43 pm

    Got a question for you electron geniuses:
    Is line over-voltage a problem only for output tubes, or do signal tubes suffer, too?
    Enquiring minds want to know.


    Last edited by deepee99 on Mon Mar 05, 2018 12:58 pm; edited 1 time in total (Reason for editing : added a word)
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    Peter W.

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by Peter W. on Mon Mar 05, 2018 12:58 pm

    deepee99 wrote:Got a question for you electron geniuses:
    Is over-voltage a problem only for output tubes, or do signal tubes suffer, too?
    Enquiring minds want to know.

    No item with a filament likes excessive voltages. Shortened life is the major issue, as performance is not affected, perhaps even enhanced in some cases. Then, there is the issue of heat.
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    deepee99

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by deepee99 on Mon Mar 05, 2018 12:59 pm

    Peter W. wrote:
    deepee99 wrote:Got a question for you electron geniuses:
    Is over-voltage a problem only for output tubes, or do signal tubes suffer, too?
    Enquiring minds want to know.

    No item with a filament likes excessive voltages. Shortened life is the major issue, as performance is not affected, perhaps even enhanced in some cases. Then, there is the issue of heat.
    Peter, do you use a Variac or are line fluctuations not an issue where you live? We have a pretty steady 121-123VAC out of the wall here.
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    Peter W.

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by Peter W. on Mon Mar 05, 2018 1:11 pm

    Peter, do you use a Variac or are line fluctuations not an issue where you live? We have a pretty steady 121-123VAC out of the wall here.[/quote]

    We are a fairly steady 118V these days. Ever since PECO gave us a double-ended service (due to excessive failures), the voltage has dropped and remained steady. And, as the recent storm has proven, a good idea. Our block and south is OK. For several blocks to the north, they have had no power since about 4:00 pm on Friday.
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    deepee99

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by deepee99 on Mon Mar 05, 2018 1:56 pm

    Peter W. wrote:
    deepee99 wrote:Got a question for you electron geniuses:
    Is over-voltage a problem only for output tubes, or do signal tubes suffer, too?
    Enquiring minds want to know.

    No item with a filament likes excessive voltages. Shortened life is the major issue, as performance is not affected, perhaps even enhanced in some cases. Then, there is the issue of heat.

    What a conundrum. Electric motors hate undervolts, as they require extra amps (and concomitant heat) to haul their mud. OTOH, light bulbs and presumably tube filaments love lower volts. I have a Swiss lamp from years ago whose bulbs are 240VAC and on 120VAC never burn out. I picked up a few spare bulbs in Zurich and have never needed them. This is going on six years.
    I lived on boats for years whose house voltage was 32VDC. Can't recall ever needing to replace a bulb. AC is murder on filaments but they'll live forever on DC.
    Sorry about the thread drift here.
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    LeGrace

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by LeGrace on Tue Mar 06, 2018 8:54 am

    This forum is littered with a sad litany of posts by me describing multiple failures I've experienced with my M125's. A bucker was easy and inexpensive to fabricate, wish I had stumbled upon this cool little gizmo sooner. Amazing the difference 4 lousy volts can make. Not one issue since, knock on wood.
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    Peter W.

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by Peter W. on Tue Mar 06, 2018 9:40 am

    This is when a true-RMS line-conditioner comes into play. Good ones are not cheap, and cheap ones are not good, but they do the job and will address many issues.

    HOWEVER!! A properly designed bucker allowing a conservative throughput at the prevailing voltage is far less expensive, and is pretty simple-minded, with the only serious issue being its capacity. Were it up to me, I would design it to 115 - 118 VAC out at 124 VAC in. At a 9-VAC drop, tariff-max voltages of 130 V may be accommodated. And, in some over-built neighborhoods with lots of central AC, this is a common condition in the summer months as the utility is trying to push more current through already-maxed-out lines.

    Where line-conditioners come into their own is with brown-outs, blinks and surges. Writing of blinks, we had about an hour of multiple blinks last Friday due to the nor'easter that blew through. And most of our neighbors lost power until yesterday. For some reason, we did not - but you can bet that the sensitive electronics got unplugged *pronto*.

    Our emergency generator got a 3-day work-out serving two neighbors. 70 hours on its clock.

    wildiowa

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by wildiowa on Tue Mar 06, 2018 11:05 am

    My daughter and son in law moved Wednesday night from a Brooklyn apartment to a new country home near Patterson NY...and the power went out within a few hours...and they are still out five days later. They are losing their minds. In Iowa on the farm I have a generator and told them that was the first thing they needed for rural living. I did not get there soon enough. If the Martians or Boris and Natasha want to take over the country in one day, cut the power grid. Chaos and mayhem will ensue. And another nor'easter is on the way....
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    deepee99

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by deepee99 on Tue Mar 06, 2018 12:10 pm

    Peter W. wrote:This is when a true-RMS line-conditioner comes into play. Good ones are not cheap, and cheap ones are not good, but they do the job and will address many issues.

    HOWEVER!!  A properly designed bucker allowing a conservative throughput at the prevailing voltage is far less expensive, and is pretty simple-minded, with the only serious issue being its capacity. Were it up to me, I would design it to 115 - 118 VAC out at 124 VAC in. At a 9-VAC drop, tariff-max voltages of 130 V may be accommodated.  And, in some over-built neighborhoods with lots of central AC, this is a common condition in the summer months as the utility is trying to push more current through already-maxed-out lines.

    Where line-conditioners come into their own is with brown-outs, blinks and surges. Writing of blinks, we had about an hour of multiple blinks last Friday due to the nor'easter that blew through. And most of our neighbors lost power until yesterday. For some reason, we did not - but you can bet that the sensitive electronics got unplugged *pronto*.

    Our emergency generator got a 3-day work-out serving two neighbors. 70 hours on its clock.
    We get by on a crystal set and Aladdin's Lamps during times such as those.
    On the spendy side of protection and steady RMS output at ~120VAC regardless of what's coming out of the wall, Peter's prolly talking about something like this Furman, which I have:
    http://www.furmanpower.com/product/ref-voltage-regulator-20a-SPR-20i
    Not cheap, but well worth it. You never see any used ones on the market.
    Even so, I have a manual-reset GFCI upstream of it and a dedicated 20-amp breaker at the box. It has never failed me, and it's nice to know the toobs will only see 119-121VAC within an input voltage range of 113-126VAC, and it's a pure sine-wave coming out. Makes a nice master-switch, as well, although I do the old fart's start-up routine of pre-amp(s) first, then power amp(s) a few minutes later; shutdown in reverse order, in order to eliminate any unexpected speaker-harming transients. In my experience, pre-amps are the noisiest on start-up, so leaving the power amp off till they settle down is a good way to go.


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    gktamps

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by gktamps on Wed Mar 07, 2018 11:39 am

    Having no shelf space for a Variac, I had previously made a 15A bucker for my M125s, but stole it for a vintage amp, so just built this twin 8A version with two voltage drop levels. Each transformer serves its own outlet/amp. Since using the buckers, the M125 power transformers run much cooler. I know - nothing new to the group here, but it's sometimes nice to see a variety of ways something is implemented.


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    jfine

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by jfine on Wed Mar 07, 2018 12:53 pm

    deepee99 wrote:
    On the spendy side of protection and steady RMS output at ~120VAC regardless of what's coming out of the wall, Peter's prolly talking about something like this Furman, which I have:
    http://www.furmanpower.com/product/ref-voltage-regulator-20a-SPR-20i
    Not cheap, but well worth it. You never see any used ones on the market.

    Yea used to have one of these, got it cheaper than this,

    https://www.pcliquidations.com/p6318-powervar-abc-1200-11

    also kept things steady ~120VAC, hospitals apparently use these.

    I never liked amps plugged into them though, somethings lost. Lucky for me each time I measure I'm around 116-118.


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    deepee99

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by deepee99 on Wed Mar 07, 2018 12:59 pm

    jfine wrote:
    deepee99 wrote:
    On the spendy side of protection and steady RMS output at ~120VAC regardless of what's coming out of the wall, Peter's prolly talking about something like this Furman, which I have:
    http://www.furmanpower.com/product/ref-voltage-regulator-20a-SPR-20i
    Not cheap, but well worth it. You never see any used ones on the market.

    Yea used to have one of these, got it cheaper than this,

    https://www.pcliquidations.com/p6318-powervar-abc-1200-11

    also kept things steady ~120VAC, hospitals apparently use these.

    I never liked amps plugged into them though, somethings lost. Lucky for me each time I measure I'm around 116-118.


    Jeff, is that your weight or your dB level you're talking about? Very Happy
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    jfine

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by jfine on Wed Mar 07, 2018 1:01 pm

    gktamps wrote:Having no shelf space for a Variac, I had previously made a 15A bucker for my M125s, but stole it for a vintage amp, so just built this twin 8A version with two voltage drop levels. Each transformer serves its own outlet/amp. Since using the buckers, the M125 power transformers run much cooler. I know - nothing new to the group here, but it's sometimes nice to see a variety of ways something is implemented.

    Hmm looks like a great idea, wish I had the chops to figure stuff like this out.
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    jfine

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by jfine on Wed Mar 07, 2018 1:06 pm

    deepee99 wrote:Jeff, is that your weight or your dB level you're talking about? Very Happy

    That's what she said cheers
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    deepee99

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    Would someone please post, or direct to a website . . .

    Post by deepee99 on Wed Mar 07, 2018 1:11 pm

    . . . a detailed schematic of a bucker xformer for up-powered VTA amps, along with a parts list and destructions even an English major can understand?
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    gktamps

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by gktamps on Wed Mar 07, 2018 3:38 pm

    Plenty available online. This one is very clear. You can use a 5Vac or 6Vac filament transformer, or the 12Vac shown in the schematics.
    http://www.geofex.com/Article_Folders/vintvolt/vintvolt.htm
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    sKiZo

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by sKiZo on Wed Mar 07, 2018 4:06 pm

    Main thing is to use a transformer that's got the beef to handle the peak load of the amp.

    Also - careful, as it is possible to hook it up backwards and BOOST the line out. Best to double check the output with a VOM before hooking up your equipment.
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    deepee99

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    Re: Transformer to Reduce Line Voltage for Amp

    Post by deepee99 on Wed Mar 07, 2018 5:38 pm

    gktamps wrote:Plenty available online. This one is very clear. You can use a 5Vac or 6Vac filament transformer, or the 12Vac shown in the schematics.
    http://www.geofex.com/Article_Folders/vintvolt/vintvolt.htm
    A 5VAC filament output would definitely prolong heater life. What about impact on performance? I use 7-volt 6922s, which are dirt-cheap compared with the 6-volt varieties, at no detriment to sound, but would going from 6 to 5VAC be too much of a step?
    I guess the absurdist in me wonders if putting a diode and a filter cap in the filament circuit would make life even better for toobs.

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