Plexi type amp owners....

Discussion in 'Marshall Amps' started by purpleplexi, May 26, 2019.

  1. purpleplexi

    purpleplexi Well-Known Member

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    Do you feel yoiur amp is particularly voltage sensitive? Think I might get a variac - not to do the EVH thing but just to ensure I' m getting consistent power. Either that or new ears.
     
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  2. Len

    Len Well-Known Member

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    A variac won’t provide “consistent” power. It’ll just drop the AC voltage by a certain amount. If the main AC fluctuates then the voltage your amp sees will fluctuate too.

    You need a “regulator”. Not the cheap ones for computers that don’t hold one output level, but a Furmann that will provide one consistent AC voltage level to your amp.
     
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  3. steveb63

    steveb63 Well-Known Member

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    I have the 1962 converted to a head, and definitely behaves differently depending on where it's plugged in at.

    My new house is terrible for power- noise.

    Way different than the last place we lived, absolutely could be the condition, or amount of power. The variac idea is food for thought.

    Hope this helps.
     
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  4. Obi Plexi-nobi

    Obi Plexi-nobi Active Member

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    I have an issue of Guitar Player where Neil Young's tech always uses a variac & a Fluke multimeter to ensure 110VAC for Neil's old tweed Fender at any venue. Len's correct about the regulator. But if you have a tech on the payroll, he can keep an eye on it during the gig. :metal:
     
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  5. Michael Roe

    Michael Roe Well-Known Member

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    I second this!
    A variac will not help.
    At my rehearsal space we have problems with varying AC voltage. A Furman like Len posted is the way to go but very expensive. A new one will run you like $1000 or more.
    I went with one of these:
    https://www.newegg.com/tripp-lite-l...VB9bACh3PtAPrEAQYASABEgK1tfD_BwE&gclsrc=aw.ds

    It doesn't hold at a constant voltage but steps it when needed. It's better than nothing and gives me at least some piece of mind.
     
  6. ampmadscientist

    ampmadscientist Well-Known Member

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    What you should ask is: how do you know the mains voltage is inconsistent?
    If you really do have un-stable power, it should be fixed by a professional.
    A power conditioner does not fix defective electricity.

    If the Plexi is 110 volt, you can use a variac to drop the voltage from 120 or higher down to 110 volts again.
    Power should not fluctuate under normal conditions.
    If the power is fluctuating, call the utility cause it shouldn't fluctuate. Or an electrician to fix bad connections in the building.

    Normally: this is detected with a chart recorder.
    The last time we saw this, it turned out to be corroded connections at a transformer on the utility pole. The utility fixed it quickly after we called them.
    Another case I looked at: the power panel had oxidized aluminum connections, causing the voltage to drop out.

    A variac does not regulate AC power.
    It will only adjust the voltage up, or down to a fixed manual setting.

    Do most applications require a power conditioner or power regulation? No. And that includes pro sound / tube amps.
    99.5% of all the guys who install these things: don't need them at all....and the device is there needlessly.
     
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  7. Metroman

    Metroman Well-Known Member

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    I use a Furman P1800 AR Voltage Regulator and AmpRx BrownBox Variac type device when I take my amp out, and I use the Furman SPR 20i at home. LTD ED Metro GMP45 head into, with all NOS glass, and Blackfaced/ODS mod 69 Dual Showman Rvb… Not only do I get consistent clean voltage,...…. Ive noticed it extends tube life, much less noise, and my amps run very noticeably cooler .
    I use the Furman to stabilize the volts at 120v, and then reduce it to 110v with BB. My wall voltage at home is consistently 125+, and sometimes 129v at the wall. I burned up an NOS 56 coated glass Marconi Osram KT66s, and my tech said I may try running the amp at lower voltages, considering it is all but an exact replica and may not like the higher voltages, and while voltage has never been consistent, its never been higher than it is now. But I know for sure my amps run a lot cooler at lower voltage, and less noise, and haven't burned up a tube in 5 years.
    Product description - BrownBox
    https://www.amprx.net/product.html
     
  8. purpleplexi

    purpleplexi Well-Known Member

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    I have checked the voltage and it doesn't seem to change that much although I haven't done it methodically. I'm in the UK and it's usually within a few volts of 240. I ask because I was playing at home the other day and the tone was absolutely quintessential - best sound I ever had at home. It was a Friday afternoon and I guess most people in the area were out. Played again later in the evening when all the neighbours were cooking/watching tv/surfing etc and the tone was just mush.I hadn't touched any eq. Today I turned on a load of electrical stuff in the house, played, turned it all off, played again, no change.
    I sometimes think it's just me but the DSL is definitely far less sensitive. That said we rehearse in a warehouse where the power is all over the place and even the DSL suffers there. I also have to say that our consumer unit at home is overdue for a change. Could be an issue.
     
  9. Obi Plexi-nobi

    Obi Plexi-nobi Active Member

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    Failed quotation- lol
     
  10. Obi Plexi-nobi

    Obi Plexi-nobi Active Member

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    I once had 136VAC at my wall outlet, following a transformer replacement in my neighborhood. I'd keep having light-bulbs burn out like crazy & my Furman PL Plus stopped working right- It just kept flashing LEDs. After MONTHS of issues, I thought to check my wall-voltage. Immediately called Light & Power company & told them they'd better get it fixed FAST. They did. WOW. I usually never get my way. lol

    Oh, and my Furman started working perfect after that. Turns out it was just a 'trouble' indicator & I was too dense to get what the tech support guy was trying to explain. In my defense, he wasn't very clear either.
     
    Last edited: May 26, 2019
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  11. Len

    Len Well-Known Member

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    I’ve read sooo many threads about how many variables change so that an amp seldom sounds the exact same twice:

    - AC voltage level
    - Where you stand relative to the speakers
    - How long the amp warmed up for
    - Your prevention of the tone (Fletcher Munson effect)

    It might not be AC voltage variation you are hearing.
     
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  12. aResilient1

    aResilient1 Member

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    I used to use a rack mounted Furman Power Conditioner in my Bass Rigs (Mesa Boogie and Ampeg Rack mount amps) but rather than go that way I went with the Furman PST-8 for my guitar amps. Basically a rack mounted Power Conditioner in a power strip. So far no issues with spikes, drops, or noise in my house or other places I've used it.

    https://www.sweetwater.com/store/detail/PST8--furman-pst-8-power-station
     
  13. JimiRules

    JimiRules Well-Known Member

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  14. BftGibson

    BftGibson Well-Known Member

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    Bogner La Grange has the variac switch, I know its not doing what a messed up current will..but,,it totally changes the amp feel & level ..you can slam much more gain at the amp with the switch on & it does change the tonal character completely. The overall volume reduces soon as you switch it on & using gain-structure-blend options..a whole new tone comes out..really good for leads cause you can juice the crap out of it and come up with lead tone that is definitely different than the amp strait up
     
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  15. purpleplexi

    purpleplexi Well-Known Member

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    Checked the juice 3 times yesterday and it was 242v every time. I'll do all the other stuff - check bias, swap cables, new strings and if that don't work swap some tubes although I think they're all pretty new.
    The plexi does this to me sometimes. When it's good it's awesome but sometimes it just throws me a curve and I end up changing everything. I always get it back somehow.
     
  16. tallcoolone

    tallcoolone Well-Known Member

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    All that is is a $150 extension cord. “Power conditioner” is a fancy sounding term that doesn’t mean anything. For true “power conditioning” you need voltage regulation.

    I have an Eaton PS800 that does regulate but that’s b/c I’m in the industry and was able to sample the thing. It is 35lbs and costs a lot more than $150.
     
  17. dro

    dro Active Member

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    Furman regulator P-1800ar to get constant power then AMP RX Brown Box to drop to 112v.
    But this is US current.
     
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  18. fifteenohms

    fifteenohms Well-Known Member

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    Buy a Variac.
     
  19. KelvinS1965

    KelvinS1965 Well-Known Member

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    More just FYI:

    UK mains voltage is specified as being 230 volts AC with the tolerance of -6% to +10% so this gives a range of 216.2 to 253 volts. Your reading of 242 volts is therefore 'within spec', so might not get much response from the supplier in terms of fixing it as some other posters have.

    Information at the bottom of the page in this link:
    https://www.spenergynetworks.co.uk/pages/voltage_changes.aspx
     
  20. purpleplexi

    purpleplexi Well-Known Member

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    I did a lot of stuff - swapped strings, cables, checked bias, fiddled with pickup heights and scratched my head till I got splinters. In the end I think one of 2 things did it. I cleaned the ppimv pot which sits in the same position a lot and I set the amp up differently. I like a tight bottom so I usually get the bright channel to where I want it and add the jumpered normal channel to give enough body to tame the brightness. This time I started with the normal channel and added enough bright channel to give it an edge. Currently loving it with normal at 12 o clock and bright at around 10 o clock. Thorpy gunshot in front. Don't think in all the time I've had this amp I've set it like that.
     
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