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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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Bob Latino
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    122v and above - why not address the issue?

    dalemurray
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    • Post n°1

    122v and above - why not address the issue? Empty 122v and above - why not address the issue?

    Post by dalemurray Mon Dec 31, 2018 1:33 pm

    I am very happy with my ST 120 but have line voltage over 124v nearly 24/7.

    Now that I am doing some other projects I am learning on other forums that voltages of 124-127 are quite common around the country.

    Is there a reason the ST-120 cannot have a transformer that can deal with voltages over 122v?

    I am using a variac but find I am endlessly adjusting it to be at 199.5-120.
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    • Post n°2

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    Post by Guest Mon Dec 31, 2018 3:40 pm

    the power transformer can be wound to suit the higher mains voltages present these days. In fact, most are these days.
    Small variations in mains voltages, in my experience, are not a big issue with modern gear, but is in older amps where the transformers were generally wound for around the 115VAC mark.
    I would guess that the VTA ST120 and ST70 power transformers are wound for higher mains voltages, but Bob is the only one that can confirm this.
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    Peter W.
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    • Post n°3

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    Post by Peter W. Mon Dec 31, 2018 4:10 pm

    The permanent solutions are either a) A true RMS line conditioner and voltage regulator (Fixed at 120 V-out) or b) a permanent bucking transformer. The latter of the two will drop input voltage by a constant, which you may determine, and may take you well below 120 Vi if that is what you want. The former is user-adjustable with the high-dollar options, but at the lower levels, are fixed at 120 V.

    We are blessed with a fairly constant 118 V, with some sagging in the hottest summer months, but seldom below 115 V. So, a transformer wound to higher input voltages would not be a good option here.
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    dalemurray
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    • Post n°4

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    Post by dalemurray Mon Dec 31, 2018 7:22 pm

    I imagine Rogue Audio, McIntosh, PrimaLuna, and insert some other tube amp manufacturer here, does not have such limitations. I could be totally wrong.

    I am not upset with the product, just wonder how manufacturers deal with this issue and is there a way to apply such a solution to this amp.
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    • Post n°5

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    Post by Guest Mon Dec 31, 2018 7:29 pm

    some transformers have multiple primary winding taps which enables the user to set it up for say 110/115/120/ etc VAC. The 'drawback' is it costs more to produce and is usually a bit larger as well.
    To a certain extend, I can 'set' B+ to a given mains supply level with my builds by adjusting the value of the dropping resistor in the power supply, but again, should the supply voltage drop or even go higher, B+ will of course follow that variation trend.
    The only way, up to a point, is to have a regulated B+ using a voltage regulator, which sets B+ at the desired level and will remain there, within the regulators circuit limits/specs, irrespective of what is happening at the power outlet.
    As for the filament supply, well tubes will work just find, usually a +/- 3V, some can take even a bit more variation. I've had tubes work just fine with 5.5V filament supply...but I would not like it to be that level for too long.
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    sKiZo
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    • Post n°6

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    Post by sKiZo Mon Dec 31, 2018 8:33 pm

    The ST120 iron is rated for a nominal 120v, and I've not heard of any catastrophic failures due to "reasonable" overvolt situations. I would think as long as your B+ stays within the specs you should be good.

    That said, I've been using a bucker here since day one to drop the line in to a more comfortable 117vac, which was pretty much average back in the day for these designs and doesn't create a brownout problem. I just think the amp sounds more natural and relaxed at those levels, but it just may be me trying to justify building the bucker ... ;-}

    Also helps that I built the bucker out of "found" items in my big ol' pile of whatever at virtually no cost.
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    Bob Latino
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    • Post n°7

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    Post by Bob Latino Mon Dec 31, 2018 9:01 pm

    It is not the AMP that can't handle the voltage, it is the TUBES in the amp that have trouble with the higher voltages. Years ago all the tubes were made in the USA, Great Britain and Germany. Today all the tubes are made in China, Russia and the Slovak Republic. Today's tubes are not as "robust" as those of 40 - 50 years ago. They use cheaper metal alloys in the filaments, plates and screens of today's tubes. Quality control is not as good. They let by marginal tubes that should never have gone out the factory door. As such, the TUBES don't stand up to higher than normal voltages as well. Over the past 13 years I have found that about 122 VAC is the upper limit for decent tube life in the VTA amps. At or above that level, tube life will be reduced and that is why I recommend a variac if you have to run your amp at voltages of 122 VAC or higher. Set the output of the variac to 117 - 118 with whatever line voltage you have coming in and you tube life will be normal. I had someone in TX with a VTA ST-120 earlier this year who had an incoming line voltage of 126.4 VAC. His DC B+ which should be normally about 500 VDC was about 565 VDC !! That is 15 volts over the limit of the quad cap. He lost a few rectifiers and had a couple of output tubes have short lives. He put in a variac and set it to 117 - 118 VAC and as far as I know, he hasn't lost a tube since. At least he hasn't Emailed me since he installed his variac in the Spring of this year.

    Bob
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    • Post n°8

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    Post by Guest Mon Dec 31, 2018 9:10 pm

    well strictly speaking, the amp is the tubes or the tubes are the amp..... Wink
    But yes, it is all about the tubes, and sometimes the caps, and as has been pointed out here, keep an eye on your particular line voltage and take the necessary actions to extend the life of the amp...or tubes...or caps.... clown
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    • Post n°9

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    Post by Guest Mon Dec 31, 2018 9:16 pm

    .


    Last edited by PeterCapo on Mon Nov 30, 2020 8:40 pm; edited 1 time in total
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    • Post n°10

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    Post by bbqjoe Tue Jan 01, 2019 2:04 am

    I just spent what I consider a small fortune building my ST120, and if Bob says to control the voltage, then by God, I'm gonna control the voltage.

    I'm completely off grid. Not a power pole for miles.
    Solar panels and forklift batteries inverting 24 volts to household current is my daily diet.
    I just put in a new 4000 watt PURE sinewave inverter.
    It isn't adjustable, and runs right at 122.
    I'm not going to chance anything, and besides, those big red variacs are kinda cool, and a great conversation piece. Smile
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    • Post n°11

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    Post by Guest Tue Jan 01, 2019 3:18 am

    .


    Last edited by PeterCapo on Mon Nov 30, 2020 8:40 pm; edited 1 time in total
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    dalemurray
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    • Post n°12

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    Post by dalemurray Tue Jan 01, 2019 6:11 pm

    I appreciate the feedback and apologize for my ignorance. I suppose I am just being anal about maintaining 119.5-120v from the variac.

    I have a "Kill a watt" on the output of the variac and the amp plugs in to the "Kill a watt". I use the variac as a power switch to the amp so I do not need to reach over hot tubes to turn it off later.

    A couple weeks back I looked and the variac was putting out 115v, I adjusted to 119v. Last week I powered it up and it was putting out 127v and I quickly turned it down. That incident is what put my question and quest in motion.
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    • Post n°13

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    Post by bbqjoe Tue Jan 01, 2019 6:18 pm

    dalemurray wrote:I appreciate the feedback and apologize for my ignorance. I suppose I am just being anal about maintaining 119.5-120v from the variac.

    I have a "Kill a watt" on the output of the variac and the amp plugs in to the "Kill a watt". I use the variac as a power switch to the amp so I do not need to reach over hot tubes to turn it off later.

    A couple weeks back I looked and the variac was putting out 115v, I adjusted to 119v. Last week I powered it up and it was putting out 127v and I quickly turned it down. That incident is what put my question and quest in motion.

    Personally, if I saw it running at 115v, I'd just leave it right there, and not bring it up any.
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    Bob Latino
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    • Post n°14

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    Post by Bob Latino Tue Jan 01, 2019 6:54 pm

    dalemurray wrote:I appreciate the feedback and apologize for my ignorance. I suppose I am just being anal about maintaining 119.5-120v from the variac.

    I have a "Kill a watt" on the output of the variac and the amp plugs in to the "Kill a watt". I use the variac as a power switch to the amp so I do not need to reach over hot tubes to turn it off later.

    A couple weeks back I looked and the variac was putting out 115v, I adjusted to 119v. Last week I powered it up and it was putting out 127v and I quickly turned it down. That incident is what put my question and quest in motion.

    A variac will alter the incoming line voltage for your amp but it won't by itself adjust the voltage UP or DOWN when your line voltage changes. What you should do is figure your highest voltages by monitoring your line voltage at various times during the day. If it did go up to 127 VAC, you should adjust the variac to output maybe 119 VAC when the incoming line voltage was 127. That way the line voltage output on the variac will float between about 115 VAC to 119 VAC as your line voltage changes. Note that as your line voltage goes up and down, the bias will also go up and down. Don't be anal about the bias on your ST-120. There will always be line voltage changes which will alter the bias somewhat. You won't hear any difference if the bias on your 6550's are .45 VDC  to .55 VDC.

    Bob
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    • Post n°15

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    Post by Guest Tue Jan 01, 2019 6:57 pm

    of course if you REALLY want STABLE AC, consider the Furman P-2400 AR. Not the cheapest, but pretty much a guaranteed 120VAC @ 20A load, there is also a 15A model, the P-1800 AR
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    • Post n°16

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    Post by sKiZo Wed Jan 02, 2019 12:15 am

    Not to forget the potential of brownout if you set a variac too low. 114vac or below is considered rough on amp life as well. Short excursions from nominal aren't really an issue - it's consistent over/under exposure that can do damage. A Kill-A-Watt is nice as you can get an average of line in over time.
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    • Post n°17

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    Post by jwb474 Wed Jan 02, 2019 3:48 am

    Here is a link to a Constant Voltage Transformer article. This is for interesting reading, not practical today.

    http://www.aelgroup.co.uk/faq/faq001.php

    Back in the day we used this technology to provide a fixed voltage to linear regulators. Today this is not necessary.
    Nowadays it is hard to find a CVT pre-designed and packaged in the power range where most of us operate with our tube amps and they are expensive


    Last edited by jwb474 on Wed Jan 02, 2019 3:50 am; edited 1 time in total (Reason for editing : spelling blunders)
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    • Post n°18

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    Post by cci1492 Sun Jan 06, 2019 10:47 pm

    PSE&G extra generous tonight...VAC = 129.1 Nuts!
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    • Post n°19

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    Post by bbqjoe Sun Jan 06, 2019 11:15 pm

    cci1492 wrote:PSE&G extra generous tonight...VAC = 129.1 Nuts!

    I'll bet your toaster can crank it out tonight!!!!
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    • Post n°20

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    Post by mikescaggs Mon Jan 07, 2019 10:34 am

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    • Post n°21

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    Post by Peter W. Mon Jan 07, 2019 10:45 am

    jwb474 wrote:Here is a link to a Constant Voltage Transformer article. This is for interesting reading, not practical today.

    http://www.aelgroup.co.uk/faq/faq001.php

    Back in the day we used this technology to provide a fixed voltage to linear regulators. Today this is not necessary.
    Nowadays it is hard to find a CVT pre-designed and packaged in the power range where most of us operate with our tube amps and they are expensive

    It is also the case that some CVTs are quite noisy (physically, not electrically) - especially if operated close to their rated capacity. Good practice would be to install it near the electrical panel to isolate that noise to where it creates no hardship.

    I am seeing 1,000-watt units for under $200 in that auction place, tolerant of a variety of input voltages and a variety of output voltages.

    Enjoy!

    https://www.ebay.com/itm/Sola-23-25-210-Harmonic-Neutralized-Constant-Voltage-Transformer-Used-/272762316350?_trksid=p2349526.m4383.l4275.c10#viTabs_0

    https://www.ebay.com/itm/SOLA-CONSTANT-VOLTAGE-TRANSFORMER-CAT-20-13-112-120VA/323606873633?_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D20131227121020%26meid%3Db073156db7cc4b2fabc4c928c77048ff%26pid%3D100009%26rk%3D1%26rkt%3D1%26sd%3D273209618492%26itm%3D323606873633&_trksid=p2047675.c100009.m1982

    There are more.
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    • Post n°22

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    Post by bbqjoe Mon Jan 07, 2019 10:54 am

    I went with this one at 20a.
    https://www.amazon.com/gp/product/B07JV8ZCG8/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1
    I put almost my whole electronics line through it.
    TV, Stereo, computer, VCR, etc.
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    • Post n°23

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    Post by cci1492 Mon Jan 07, 2019 11:24 am

    I have the one bbqjoe has but went with a 6.3 filament TA setup as a bucker after the variac started tripping my breaker. Thermister took care of the problem, the bucker no longer cuts it at almost 130VAC.
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