PSA for tube amp owners, yes this means you....

Discussion in 'Marshall Amps' started by Michael Inglis, Aug 18, 2019.

  1. Michael Inglis

    Michael Inglis Active Member

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    Please pass this info along if you see someone post about a related issue, i think this issue is more common than we think and is being overlooked. Thanks MI

    Ever have a problem Biasing your Power Tubes? Maybe the pot is maxed out and your bias is too low or you set the bias at an average setting only to come back later and see that the bias is now running hot? You might get on this forum and people are quick to tell you that you need to change a resistor etc. But a recent experience of mine has revealed a new source of this problem. Line voltage fluctuations outside what is considered normal. In other words your outlets in your home are fluctuating voltage more than is deemed "normal". I have a brand new 100w Marshall DSL100HR that kept going through the V5 power tube. The tubes would sometimes bias high enough and other times wouldnt. I have the bias set between average an hot at about 78mv a side. Considering what my plate voltage had been reading, 78mv was closer to average than hot. And at times i had the bias even lower and still had tubes go bad. So it turns out my line voltage in the am is about 118v but in the daytime it has dropped as low as 100v. It never made sense that i needed to change a resistor cause this is a new amp using the tube type (EL34's) it was designed for. So this is what was happening. Id set the bias during the day when my line voltage was likely low say 105v and id have a hard time getting the bias up to my preferred 78mv so id settle on the highest i could get them while still being matched. Sometimes id have to roll the tubes to get them to bias higher. So then my bias pots would be maxed out. Then the next morning before work id go power up my amp for my morning practice routine and at this time of day my voltage is closer to the 120v i should be seeing. Because of this my bias has now skyrocketed and im marching my Power tubes to their early demise. CHECK YOUR LINE LEVEL AT SEVERAL TIMES THROUGHOUT THE DAY. This problem went over my head cause the few times i checked the outlets in my home they were "close enough" its only when you zoom out and look at the bigger picture that what was happening becomes clear. In my case i believe it could be a few things causing above average voltage fluctuations but after checking the breaker box voltage i believe my next move is to call the power company and have them come out an see if this is an issue on their end (EDIT: It was an issue on their end, they said they'd fix it but my voltage at the box is still too low. I found a solution though and I posted about it. And I won't cost you $1000, more like $35. It's the opti ups 2000 regulator.). If not ill have to track down where this power is getting lost. In this case i believe its a power company problem not a wiring in my home problem. Anyways this info should be suggested alongside the "you should lower the bias resistor" advice. If the amp is new and the tubes being used are what the amp was designed to handle you shouldnt need to change a resistor. That advice is likely just so common its being suggested without any consideration to the fact that a new amp not biasing high enough is likely not due to a resistor. If your amp is new and your using good tubes that are the type the amp was designed for you should never have to change a resistor or a bias pot(infact doing so when voltage fluctuations are your problem would just make things much worse as your bias would then be jumping even higher when your line voltage goes back to normal). Anyways, please pass this info along so others in this situation might avoid burning through power tubes as i did or worse!

    -M. Inglis

    Edit: This has fixed my voltage problem and keeps my voltage much much closer to 120v. It boosts your voltage if the line voltage goes below 116v (on my unit, this may vary by +/- 1v). So when my line voltage is at 116v or below the regulator boosts it by about 10v. And if your voltage ever gets too high it will do the same thing. This unit is more precise than the more expensive units but it won't work if your line voltage drops dramiticaly(under 100v for example). More expensive units like a Tripp Lite can handle greater fluctuations but won't regulate until your line voltage is below 102v so it requires greater fluctuations to be useful. Anyways I'll post the specs for this unit now since I've already left a comment describing the pros an cons in detail in another thread of mine. Last thing I'll say is this unit is exactly what I was looking for an so far it works great, many not as good of quality as others but there's nothing else in this price range that actually works. Screenshot_20190825-062954.png Screenshot_20190824-013724.png
     
    Last edited: Aug 26, 2019
  2. Lance Chambers

    Lance Chambers Well-Known Member

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    Been there, done that...........got a t-shirt! :dude:

    My home outlets are a consistent 125 SI units of electromotive force (in my sound room) and I bias all of my amps hot.:jam:
     
  3. CraigP

    CraigP Well-Known Member

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    Line conditioner with voltage regulator are expensive but very helpful with preventing this. Expensive and not "fun" but worth the investment IMO
     
  4. Michael Inglis

    Michael Inglis Active Member

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    Certainly will be investing in a line conditioner/regulator but theres no way it will be a Furman right now. I know the less expensive ones are nowhere near the efficiency of a Furman but whats generally accepted as the best option without spending an arm and a leg. Im sure there will be a Furman in my future cause i seriously dream of a day when i can plug into my amp and have a consistent sound. When my voltage is good that amp sounds incredible but when its off not as much. Im aware the big draw with units like the Furman is having the correct impedance for a guitar/audio application but right now id settle for not too loud and able to keep my voltage whiten regulated voltages. In other words 120v ±10v.
     
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  5. ampeq

    ampeq Well-Known Member

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    I own a machine shop and I can watch the RPM on my CNC machines go up and down a couple hundred RPM's. I'm the only 3-phase power on my road to, so nobody else is sucking the power down, it just plain sucks. (On a 3-phase power line you only get 208v anyway) This place would kill an amp, but my home seems ok. A power conditioner is the way to go if you have a lot of fluctuation.
     
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  6. Michael Inglis

    Michael Inglis Active Member

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    Honestly i think thats true but i cant afford a $1,200 power conditioner. Even if i could how would i convince the GF that we need to spend $1,000 on something that to her probably would seem like an incredibly unnecessary expense lol. But i have been looking into cheaper units for now. But most of them dont regulate as much as "cushion" and keep the voltage in a more consistent range. Ive noticed that anything below 110v and my amps bias drops too low and my tone is mush. And the only time we get above 110 is early morning an late night. If anyone else has any suggestions other than sell a kidney for a Furman im all ears???? Im still waiting on the power companys response. But i have a feeling theyll say that they are supplying enough as per their terms of service. It would be just my luck that they only guarantee at least 100v at a minimum. But at the same time that seems unsafe, we will wait and see.....
     
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    A fluctuation of more than a couple volts is not normal.
    100 volts AC is not normal.
    If the voltage fluctuates more than 118-120 (2 volts) the power company should fix the problems.

    But you may get a power company which does not maintain, in which case you can use AC line voltage regulation but this can become expensive.

    [​IMG] Input 89-147 volts AC output = 120 volts. Rated 10 amps. About $160.00
    VOLTAGE REGULATION
    Voltage Regulation Description Maintains usable 120V nominal voltage during brownouts as low as 89VAC and over-voltages as high as 147VAC. Input voltages between 114V~127V are passed through unchanged.
    Overvoltage Correction Input voltages over 128V (+/-3V) are reduced by 10%
    Brownout Correction Input voltages between 113V (+/-3V) and 103V (+/-3V) are boosted by 9%.
    Severe Brownout Correction Input voltages below 102V (+/-3V) are boosted by 19%.
     
  8. Micky

    Micky Well-Known Member VIP Member

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    This does not apply to me.
     
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  9. ampeq

    ampeq Well-Known Member

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    I designed test & assembly fixtures for APC (Now Schneider Electric) years ago and they had a battery backup unit that ran off the battery full time and kept itself charged. I don't know if they still have stuff like that but it was only about $125 and worked ok on computers. Never tried one on an amp though so make sure whatever you buy will take the draw. You should be able to get one for your amp for under $200, those big ones you probably looked at are whole house units or for banks of computers, 1 amp will require a lot less.
     
  10. Adrian R

    Adrian R Well-Known Member

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    Just bias conservatively and you should be okay....assuming your tubes are well broken in and stable at idle...
     
  11. Lance Chambers

    Lance Chambers Well-Known Member

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    I tested the outlets again today with a load on my house current (air conditioning, etc) and they were a consistent 123 - 124 SI units of electromotive force throughout.

    :band:
     
  12. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    "If your amp is new and your using good tubes that are the type the amp was designed for you should never have to change a resistor or a bias pot..."

    Changing the resistor is common and frequent, depending on which tubes you can buy.
    If you can buy factory spec tubes then you won't need to change resistors.
    Most tubes you buy probably won't match the original factory tube, this is normal.
    Not all tubes are the same, there is wide variations.
    This is why tubes are matched into sets. If the tubes were all the same there would be no need for matching into sets.

    Power fluctuations are rare. Power is pretty consistent over most of the country but there is probably 1% where it is out of spec.
    Most people will not need voltage regulation or power conditioners...
    But where you do have this problem, then it can cost some money to stabilize bad voltage.
     
    Last edited: Aug 19, 2019
  13. anitoli

    anitoli Well-Known Member

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    When you stop letting someone else control YOUR money, it all becomes crystal clear..............
     
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  14. ampeq

    ampeq Well-Known Member

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    That should be fine. My single phase voltage at the shop runs about 118v but goes up and down a little. The biggest thing this hurts are TIG welders, I had a new $4000 machine and it worked great. I switched to 3-phase power, went to use it and it would not jump the arc. I said here we go... then it dawned on me what I did. Inside of them is a jumper you change and BANG, it works again. Going from 220v or so down to 208v is a big deal. I have played a couple amps at the shop but never noticed anything wrong.
    AMS showed one above that might work for you, or look up "line conditioners" as well.
     
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  15. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Use a power conditioner. Problem solved.

    Incidentally, with all other voltages being stable, if you INCREASE the bias voltage, the tube runs COLDER. If your bias supply cap should fail, that's when your tubes red plate and before long your output transformer dies screaming.

    However, bias voltage does not track perfectly with plate voltage if you have a line voltage variance. It's close, but not close enough if your bias is already on the critical edge.


    When biasing an amp, you SHOULD use a variac and set the line voltage to what the amp is going to be living with on the road. Since you don't actually KNOW that without a power conditioner that regulates line voltage to your amp, it's a guessing game. When in doubt, bias a bit cold.
     
  16. Michael Inglis

    Michael Inglis Active Member

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    They FIXED IT they fucking fixed it!!! Last night the guy from the PC went and adjusted the Capacitor Bank....lol which didnt do shit. But he said he was gonna have the power company up the voltage for this time of year. I woke up like a kid on Xmas and checked the voltage. And it was still as it always was, dropping by the hour. It had gotten down to about 110v but then the next time i checked it.....122v!!!! I dont remember the last time we got 122v. Now with that said it will still likely fall/rise with the demand but at least it will be within reasonable levels now. My amp sounds so fucking good when its biased just right at 78mv and now that i have better voltage ill have it at 78mv or close more often. Damn im so happy!!!!

    EDIT: Ill check the Plate voltage later once i find what time of day im at the average line voltage and set my bias accordingly.
     
    Last edited: Aug 19, 2019
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  17. Exojam

    Exojam Well-Known Member

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    Ahhh, I just run all my gear through 2 EquiTech Balanced Power Transformers.
     
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  18. Michael Inglis

    Michael Inglis Active Member

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    I still work as a welders helper from time to time. Ive always meant to do it full time and take the community colleges classes so i could get a job as a welder full time a little quicker. Thats gotta be a pain in the ass dealing with low voltage trying to weld. Hell it can be hard enough stacking dimes with good voltage, i cant imagine trying to do it with low voltage/fluctuations. Im sure im not telling you anything you dont already know but on the job sites I typically work on we use generators for everything (grinders, sawzall, etc.). Most of the time its stick welding water lines in summer time in trenches that get up to 115 degrees lol . Anyways like someone else said it might not be a bad investment to get you one. Hell theres tons of them on the used market that are still in great shape and much more affordable.
     
  19. Michael Inglis

    Michael Inglis Active Member

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    I have no doubts that is an excellent solution that exceeds anything a Furman could do but those Equitech units are 2-3x as much as a Furman unit and the Furmans are already too much at $1,200. Im not saying i could never afford one, it just wont be anytime soon. I also have no doubt it would be an excellent investment considering my goal is to get as consistent a tone as possible regardless of where im playing. You run those Equitechs at home only or take them with you when your gigging/jamming?
     
  20. Michael Inglis

    Michael Inglis Active Member

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    I saw a few of those Tripplite's but the ones i was looking at were only activated at about 105v. That one is perfect, i seriously think its the winner. 114v isnt "perfect" but its still in the range of usable (within the +/- 5% that the amp was designed to operate with) and worth the investment considering the specs. Im surprised i missed that one cause the triplites were thpe ones i was looking at the most. Thanks for posting the specs, if you hadnt i would have assumed its just like the ones I already looked at. $160 is just about what im comfortable paying right now too.
     

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