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Protecting Vintage Tube Amps From Wall Amps

Discussion in 'Glowing Bottle Tube Amp Forum' started by keithb7, Jun 18, 2017.

  1. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    I have a buddy with some pretty nice vintage gear. Original great looking and sounding caps still in there. No noise, no blistering, nothing. The amps sound great but have me cringing when he plugs them in to 120V every once in a while to play them.

    What can he do to minimize damage if an e-cap decides to take a short cut to ground? It scares the h e l l out of me. I don't recommend plugging a 1959 100% original amp in to sample once in a while.

    I was thinking, what if I built him a light bulb limiter? The stock 5F1 had a 2 amp fuse. If I used a 60W light bulb that would limit him to 2 amps in total. Right? 120/60 = 2. The amp would play and sound as it should. 100W bulb would deliver 1.2 amps total.

    Besides talking him into new e-caps, what method can I help him set up, to protect his 2 very fine 100% stock tweed amps. A Tweed Champ, and a Tweed Harvard. Something must be done....I hate the thought of blowing a transformer.
     
    Last edited: Jun 18, 2017
    Jugador, JohnnyWahlroos and 24 track like this.

  2. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    Pics for those interested:

    1959 Champ
    [​IMG]

    1959 Harvard
    [​IMG]
     
    bryan83, Chicago Matt, Dan R and 6 others like this.

  3. gordon schumway

    gordon schumway TDPRI Member

    13
    May 5, 2011
    Canada
    Wow, those look impossibly clean!
     
    Chicago Matt and Piggy Stu like this.

  4. dsutton24

    dsutton24 Poster Extraordinaire Gold Supporter

    Dec 29, 2010
    Illinois
    Wall amps? What is your recommendation based on?

    You've got some things mixed up. A current limiter built out of a lightbulb will deliver what voltage to the amp's plug? That's the problem, it's going to depend on a lot of factors. Line voltage, the current draw of the amp, the impedance of the light bulb. That last one will change depending on temperature. And so on. If you limit current without regard to voltage the amps aren't going to sound right.

    If your concern is his line voltage, what is his line voltage? You know it's going to vary, maybe considerably.

    What is his attitude about the amps? If they're players to him, then let him play them. If he prizes them as all original, talking him into new caps will be doing considerable harm to the value of the amps.

    Here's the deal as I see it. The amps are coming up on 60 years old. Their days as 100% original amps are numbered. In fact, their condition is something close to miraculous.

    Amps that are used a lot tend to stay healthy better than amps that are pulled out of the closet once a year. Electrolytic capacitors that aren't used deteriorate.

    If you need to lower the line voltage to the amps think about a pair of transformers set up to buck the secondary voltage down a bit. A Variac is also a possibility. Bear in mind that ground integrity is a concern through any boost / buck transformer, but since the amps are 100% original I'm guessing that safety is going to be a secondary concern.
     

  5. JustABluesGuy

    JustABluesGuy Tele-Afflicted

    Age:
    60
    Sep 2, 2016
    Houston, TX
    I was thinking the same thing. Either rarely used closet queens, or professionally restored.
     

  6. charlie chitlin

    charlie chitlin Doctor of Teleocity Silver Supporter

    Age:
    56
    Mar 17, 2003
    Spring City, Pa
    You know the answer to that.
    You can have an all-original amp, or an amp to be played.
    You can geek out on your original thing, take the back panel off, post pics on the internet, and show it to your gear geek friends, or you can service and play it.
    Anything else is irresponsible.
    Someone who respects this stuff so much should be aware of what it means to take a rare transformer out forever.
    You can keep the original caps in a baggie and put them back in.
    Anybody who thinks you can't duplicate original solder joints isn't very handy with the iron.
     

  7. String Tree

    String Tree Doctor of Teleocity

    Dec 8, 2010
    Up North
    It all depends on why he bought the Amp.
    Investment or, player?
    If it was as an Investment, he should never plug it in again and, pack it so it never gets any Humidity it, dust.
    Player, replace the Caps and let it Rawk.
     
    OlRedNeckHippy likes this.

  8. jackinjax

    jackinjax Friend of Leo's Silver Supporter

    Sep 11, 2016
    Jacksonville
    I wouldn't recommend using a lamp (light bulb) in place of a fuse. The 2 amps you arrived at is what the lamp itself draws. And, whereas, lamps are sensitive to voltage, seeing a higher than rated voltage only makes it burn brighter for a shorter period of time, but, not nearly fast enough to protect the amplifier.
     

  9. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    I'm no electronics guru and I was thinking I could somehow protect the current that could get into the circuit. In my own silly way, maybe limiting wall current in would help somehow.

    I suspect his wall voltage is 120 to 122V. As mine is.

    I know what the correct answer is. Re-cap, re-cord and rock out another 50 years. They are not mine, so I won't be doing this.

    These are both closet queen amps. Bought from original owners. He pulled the rear panel off the 5F1 for the first time since 1959 he figures, yesterday. The rear panel was still partially stuck to the tweed cab covering, from assembly.
     
    24 track likes this.

  10. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    As dsutton mentioned, a light bulb limiter isn't going to work for playing; the voltage drop is going to be large. Besides, you've got the math backwards: it's 60/120 to get the current, which is 1/2 amp. (.5a x 120v = 60w).
     
    mitchfinck and jackinjax like this.

  11. MrGibbly

    MrGibbly Tele-Holic

    529
    Apr 19, 2014
    SATX
    Beautiful amps! I use a Brown Box to bring the voltage down and an APC line conditioner to reduce noise and protect against surges.
     
    nocastermike likes this.

  12. 24 track

    24 track Poster Extraordinaire Silver Supporter

    Nov 6, 2014
    kamloops bc

    Hey Keith, If you need to borrow a variac let me know you can use mine if you need it, its Identical to the pic above PM me if you need it!

    ( I think my batteries are going in my keyboard it keeps dropping letters)
     
    Last edited: Jun 18, 2017

  13. MrGibbly

    MrGibbly Tele-Holic

    529
    Apr 19, 2014
    SATX

  14. Frontman

    Frontman Tele-Meister

    436
    Jul 10, 2014
    Tokyo
    A bit of epoxy will keep your settings locked in.

    Where I live, wall socket voltage is 100v, and when buying an American amp, many people change the internal transformer. It's a common mod which most shops here can do quickly.

    If the amps are too nice or valuable to mod, then they may be too nice or valuable to play. I have occasionally bought a piece of classic gear intending to use it, but found to to be too good to use. As I am not a collector, I sold these things to collectors, usually for a tidy profit. My own gear gets played hard, and it shows.

    Three years ago I got a 57 Tweed Champ which still had the tag on the handle. A guy in Portugal offered me big money for it, sight unseen. I never plugged it in, but sold it for 5 times what I paid for it.
     
    keithb7 likes this.

  15. charlie chitlin

    charlie chitlin Doctor of Teleocity Silver Supporter

    Age:
    56
    Mar 17, 2003
    Spring City, Pa
    The film production house I worked for years ago had at least a dozen variacs.
    It sees to me they had a stop that the pointer hit.
    It may have been adjustable or just a sheet metal screw to stop the pointer
     

  16. FenderLover

    FenderLover Friend of Leo's

    Jun 11, 2009
    Minnesota
    The amps may sound good, or even great, but it's probably safe to assume that a 60 year old amp doesn't sound anything like it did when it was new. No one would drive a car that old with its original tires and oil. The amps should be maintained or left on the wall for a museum.

    Since he is willing to roll the dice and turn them on occasionally, the impending damage is no different than the jump to maintaining them, unless he intends to sell them soon to another collector.

    Let's be honest, they're nice amps, but they're not priceless. Educate him, and he'll do what he wants. He'll soon have two non-original amps worth half of what they were, or two maintained amps that most collectors would still want.
     
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  17. slider313

    slider313 Tele-Holic

    Age:
    60
    942
    Jan 6, 2011
    NC
    No variac will protect the amp if an original electrolytic cap in the power supply shorts. Talk him into replacing the electrolytics and bagging the originals!
     
    RLee77 likes this.

  18. xafinity

    xafinity Friend of Leo's Silver Supporter

    Dec 24, 2015
    my Mom's basement
    The variac is not to 'protect' the amp although it can keep some out of spec voltage damage down..
    If a chassis is built on the 107-110 volt spec then it will sound way different at modern American 120-125 volts. Remember the transformer does not offer what the rest of the chassis expects unless it is fed the expected primary voltage.
    Likewise if your DRRI built to function at 120volts is browning out because the best you can get out of your mains or a venue mains is 100-105v then just crank up the volts to 120 on the variac.
    --- all together now in chorus with a high pitch
    variac, variac, variac..
     
    Last edited: Jun 18, 2017
    David Barnett likes this.

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