variac on vintage amp

Discussion in 'Amps and Cabs' started by rocknrolldaniel, Nov 23, 2005.


  1. what are the benefits of running a vintage amp on a variac to set the voltage 110v? Does it change the tone at all? Is it simply let the PT run cooler?
     
  2. rockstah

    rockstah Member

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    in a vintage BRITISH amp that is...
    in all my reading it seems it would make the sound "browner" which makes sense alittle less juice would make it warmer.
     
  3. yeah I've heard that, I'm asking because the voltage coming off of an outlet when these amps were designed was 110v, the 120v of today.
     
  4. JWK

    JWK Member

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    I clip leads from my meter to the filament circuit. I adjust the variac until the filament voltage is between 6.0v and 6.3v. Then I adjust the bias voltage. Then I play the amp.

    You guys make this way too complicated.
     
  5. drbob1

    drbob1 Silver Supporting Member

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    My JTM45 sounds a little strident at 120v, but sounds great at 114 so I use the variac to keep it there. My 59 Bassman is biased a little hot at 120v, but sounds and works great at 110v. If the bias voltage is good at 120v, the filament voltage isn't too high and the amp sounds good, you don't need a variac BUT if you have one, why not use it to keep the voltage where it should be?
     
  6. sundaypunch

    sundaypunch Member

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    I agree with that. Also, in some places you can end up with as much as 124v or so out of the wall.
     
  7. drbob1

    drbob1 Silver Supporting Member

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    Yeah, since the wall voltage isn't consistent, I often check the voltage coming out of the Variac to make usre it's correct...
     
  8. SQUAREHEAD

    SQUAREHEAD Supporting Member

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    SO... let me get this straight here.
    You guys can here a difference in tone by varying the voltage just from 120 to 114??
    Wow!!

    I know I've tried it to 90 or so and adjusted everything accordingly... and yes a huge difference...
    But even little changes make a difference too!?

    Keith
     
  9. sundaypunch

    sundaypunch Member

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    I think that most people using Variacs aren't worried about tone as much as pushing old amp components with way more current than they were designed for. I have a blonde Bassman and don't worry about it. If I had a nice tweed Bassman I'd probably go the Variac route.
     
  10. what kind of variac do you need? Do the amps of it matter
     
  11. Damon

    Damon Member

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    Thanks JWK, makes perfect sense. On another forum someone said his filaments in his old amp were at 6.9V when plugged into today's wall. That's almost 7-volt ("P" rather than "E" for European tubes) range. Probably not good for optimizing tube life.

    I'll have to do this sometime with my old Altec and Ampex gear, to see where they like to run. I have a Hammond Line Voltage Regulator, which is basically an isolation transformer that has a tapped secondary, lets me go from about 100 to 130... should be good enough... one more thing to carry!
     
  12. chuby galoso

    chuby galoso Member

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    yes the amps mater. make sure the amperage of the variac is high enough to run all the stuff you will have on at the same time. and if you have a rig that uses old and new then you might need two variacs to run the rig. modern transformers have an industry standard 118 volt primary winding. old stuff is mostly 110 and sometimes 115 volts for the primary winding. this means if you put 120 or so volts on a 110 primary than you can wind up with ten or twenty more volts on the plate and your filement winding will be way high. it always cracks me up to see a tech bias an amp thats pluged right into the wall not even knowing what the primary winding is geting. and try to get one with a meter on it so you can walk back to your rig now and then and keep an eye on the voltage, than you can adjust the diel to compansate for the wall. or even beter get a power regulater to run the variacs off.
     
  13. daneswede1

    daneswede1 Member

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    I almost bought (And WiSH I did!) an all original 1 owner 1969 Marshall Small Box 50 Watt Tremolo head. THis amp was untouched since new. The cleanest Marshall I ever saw! it actually only sold for $2500! I couldnt believe it i dont know what the going rate on a 69 50 watt trem head is but im sure its more than $2500 bucks?

    I asked the guy who was selling it on Ebay if it needed a Variac or anything special to run the head according to voltage regulations in the USA? He said since he bought it new in 1969 he had always ran it in the USA without any variac or anything. It had a three prong chord installed in it! I am quite the novice when it comes to old Plexi type amps and being able to run them with or without a variac or special device according toi US voltage specs and such??

    Still wish I had bought it!
     

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