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Amp cramping...

Discussion in 'Amp Central Station' started by Matt Sarad, Oct 9, 2018.

  1. Matt Sarad

    Matt Sarad TDPRI Member

    18
    Apr 29, 2003
    I have two Tweed Deluxes. One us a beat up original from the late 50s. It has original Tung Sol tubes in the power section. The preamp tubes have been replaced. Last week the original capacitors finally gave up the ghost and were replaced. The other is a Victoria. It has NOS GE tubes for the most part. A newer 12ax7 was put in after a preamp tube died.

    These Amps sound spectacular at rehearsal with my new Tele, a butterscotch 2018 MIM with Fender Noiseless pickups added by the seller. The cramping begins about 45 minutes into outdoor gigs with both amps. They lose volume and clarity, getting a brown sound that lacks definition. I started my outdoor Sunday gig with both amps singing: tone at 9 and volume at 3. I use a Reverb and Tremelo pedal along with a tuner. After about 45 minutes, both Amps lost their vitality.

    As far as I can tell, extension cables, the classic orange found in most garages, offer too much resistance and give voltage under 120, which seems to be the new standard. The other possibility is ?

    I tried my 19 year old Tech21 Trademark 60 at rehearsal last night and it sounded very nice. While it lacks the tube round, warm sound, it cut through without any hesitation. I was using my ‘65 Melody Maker with T Top PAFs I bought back in ‘72 when I was a junior in High School. I will plug in the Tele next time and see what I get.

    Thanks for reading.
     

  2. schmee

    schmee Friend of Leo's

    Jun 2, 2003
    northwest
    I can't use those small amps outdoors or big venues. Too nasty. Doesn't matter if you mic them or not. All you get is louder nasty. I think it has something to do with SPL, sound pressure level or something. I cant even use a BF Deluxe at an outdoor event.
     
    Jakedog, Matt Sarad and brookdalebill like this.

  3. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    I can run my Coc Ultimate 5e3 all night long without any difference in it’s ‘vitality’.

    Maybe your ears are just getting fatigued? It happens. I get tired of listening to any of Hot Rod amps for an evening. Whatever frequency it is, that they produce differently than my amps, just kills me after about a set or so.
     

  4. JD0x0

    JD0x0 Poster Extraordinaire

    Age:
    28
    Feb 22, 2009
    New York
    'brown sound' suggests some sort of voltage drop or sag. Possibly a resistor getting hot, then drifting up in value causing more voltage drop. Could be something wonky with the tube rectifier dropping more when it's up to temp.

    You did say these amps were original.. Carbon comp resistors tend to drift a lot, and tend to be more sensitive to temp and humidity conditions.
     

  5. sliberty

    sliberty Tele-Afflicted

    Mar 19, 2007
    East Brunswick, NJ
    Might need to replace the rectifier tubes
     

  6. nojazzhere

    nojazzhere Friend of Leo's

    Age:
    66
    Feb 3, 2017
    Foat Wuth, Texas
    You say you were at an outdoor gig....could you have experienced a long extension cord voltage drop? Outdoor gigs can be notorious for unreliable/inconsistent power.....
    At rehearsal, does it occur after 45 minutes?
     

  7. Matt Sarad

    Matt Sarad TDPRI Member

    18
    Apr 29, 2003
    All the tubes have been checked and are good. Caps were replaced in the Fender.

    At rehearsal yesterday my amp turned into the Neil Young sound after an hour+/-, so we learned Cinnamon Girl.
     

  8. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    These amps need to be analyzed...voltage charts and biasing...over the period of time it takes for their operation to degrade...beginning measurements with following up measurements every 10-15 minutes.
     
    Silverface and H. Mac like this.

  9. Matt Sarad

    Matt Sarad TDPRI Member

    18
    Apr 29, 2003
    I would mostly agree with that statement. It is my understanding that Tweed Deluxes don’t get biased. Too darned simple in construction.
     

  10. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    All amps get biased. Cathode biased amps do not usually have the basic biasing resistance value changed in order to bias the amp. However, every time a different power tube/tubes is/are installed, the amp gets biased by the interaction of those static circuit components and the variance in the performance parameters of the actual tube/tubes that are installed. I once looked at about 12 NOS 6V6’s in a BF Champ. There were no close matches. I observed plate dissipation numbers from 80% all the way to 150%. I have also adjusted the bias in a SF Champ from a very high 20 watts of plate dissipation down to 14.7 watts of plate dissipation. Big sonic changes along the way....and I put it back stock with the original 470ohm bias resistor that was still dead on in its value. Magnificent amp...best BF/SF Champ I have ever heard.
    I prefer to know the numbers when I install tubes whether the amp is cathode biased, non-adjustable fixed bias, or adjustable fixed bias. In the case of the OP’s amps, it is very important, imho. Voltages are important, ime, as are Resistance, and Current. I would also want to observe the wall voltage even though I don’t know if there is any correlation since the amps are acting strangely in more than one location. I still want to know the wall AC anyway....it is a habit that has its purpose for me. The amp can get reviewed by a change in the wall voltage, too. Some people prefer to run amps at the voltage that was ‘normal’ for the time of the design. Some are said to run amps below that AC voltage for sonic reasons????
     
    H. Mac likes this.

  11. Matt Sarad

    Matt Sarad TDPRI Member

    18
    Apr 29, 2003
    Thanks for the clarification. Exactly how does one bias a Deluxe? I have been in conversation with my luthier who also builds and works on amps. He tells me his house voltage is 127.

    My amps sound fine at home with all new wiring that has replaced knob and tube, but I don’t play them for extended periods of time. I guess I should get a voltage meter and start checking what I get in two other rehearsal locations and live gigs.

    I can get voltage regulators for about $80.
     

  12. flatout9

    flatout9 Tele-Holic

    816
    Aug 6, 2009
    Houston, TX
    An idiot chiming in, here... Since it's an outdoor gig, would humidity have any effect on the speaker cone?
     

  13. JD0x0

    JD0x0 Poster Extraordinaire

    Age:
    28
    Feb 22, 2009
    New York
    Neil Young sound is largely 'blocking distortion' an unwanted effect when there's too much bass.. Pretty common on tweed amp when pushed hard..

    http://www.aikenamps.com/index.php/what-is-blocking-distortion


    Something is wrong if this is happening over time. IME, most amps tone don't really change much, when they're in healthy working order. You can play for 10 minutes or 2 hours and the amp will basically sound the same. You may have a leaking coupling cap or something.


    Also, please ensure ALL the original electrolytics were replaced. I have to mention this, because there's been enough times I've heard 'Serviced' or 'New Caps' and then the bias caps aren't done, and/or the bypass caps in the preamp aren't done. They should have ALL been replaced, not just the big filter caps..
     

  14. JD0x0

    JD0x0 Poster Extraordinaire

    Age:
    28
    Feb 22, 2009
    New York
    Huh? More resistance would DROP voltage, not increase it... Also, your problem sounds like too little voltage (somewhere), not too much.. Too much voltage (in a tweed) would likely give a cleaner tighter sound, up until components started cooking from over voltage (if it's extreme enough).
     
    nojazzhere likes this.

  15. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Tech time.... live circuits are not the safest places to be. Without experience, one might seek out help...experienced help. Or...start doing some reading. Learn to understand schematics, tube pinouts and functions, etc.... on a simple side of things, learn how to read current draw. Buy a bias metering kit that also reads plate voltage. That keeps one away from direct contact with voltages for safety reasons. I use the transformer shunt method which is the quickest...and the most dangerous..method.
    Matt, it is not that you need to set the bias in these two cathode biased amps but rather that all voltages and bias situations need to be understood. One can rebias that amp installing different tubes that yield different operational parameters.....they draw different current levels.
    As noted by JDOXO earlier, there is likely to be a voltage sag/current draw increase going on during prolonged use that needs to be pinpointed and dealt with. The problem may not be directly connected to the power tubes...
     

  16. Matt Sarad

    Matt Sarad TDPRI Member

    18
    Apr 29, 2003
    Thanks for the in-depth education regarding my amps.

    I will not be purchasing anything other than the voltage ohm meter( if that’s what it’s called.) electricity may be your friend, but I take no chances with death anymore after a stay in ICU and rehab facilities after a crippling bicycle accident 5 years ago.

    I will discuss this with my Tech.
     
    Wally likes this.

  17. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Matt, you may need to sit and play the amp while the tech does more productive things. The tech can take measurements occasionally along the way until the amps start to be ‘drawn down’.....then the measurements taken at that time can be compared to the baseline figures taken earlier. Or.....You might do this before going to the tech. Put the amp in play mode and play to ascertain that all is normal. Then, let the amps sit for a while....as long as it takes when playing for them to exhibit the symptoms. Plug in and see if the amps have changed. This info would be helpful to the tech...especially if the symptoms appear without playing. You won’t have to sit there playing, right?
    Have you ever taken a look at the power tubes at the time that the amps change their output? Hav you ever taken note of the heat produced by the power transformer?
     

  18. Matt Sarad

    Matt Sarad TDPRI Member

    18
    Apr 29, 2003
    I thought I had spotted the problem a few weeks ago when amp lost volume and the rectifier tube looked like it was dying. The other tubes were nice and bright while the rectifier looked like the last, fading embers of a campfire. It tested out fine and five caps were replaced.
    I haven’t thought about checking the transformer.
    At our gig last Sunday both the Fender and the Victoria lost volume, sparkle, and clarity. My Tele went from ice pick in the forehead to dull pencil on binder paper.

    I will talk to my tech about sitting down for an hour( $40-$80 depending on what happens). He is in a bit of a slow period. He could retire since he has a million in Apple stock he bought since the beginning, but he like to stay busy.
     

  19. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Testing of tubes with a tube tester is not indicative of how the tube works in a live circuit. At best, most tube testers are good for indicating that a tube will NOT function at all.
     
    Silverface likes this.

  20. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

    Age:
    66
    Mar 2, 2003
    Lawndale CA
    That doesn't sound right, and if true he needs to contact the utility company. Something is wrong. I just had new 200-amp service installed and discussed supply voltage with my electrician - the current standard in most areas is 121VAC, and he won't work on systems where normal equipment does not limit voltage to a constant 121 - he calls the utility company, which fixes the problem for free. Most major utility companies are upgrading to digital meters, which also control the voltage and limit spikes. You don't note where you're located but I'd be very hesitant to use a tech that hasn't had his supply voltage issue taken care of.

    However, tweed Deluxe at 112-121 VAC or so will work fine. Performance will be a little different - but not anything like what you are talking about. Those are heat related transformer issues, power supply parts failing, or bad tubes.

    I'm concerned that the ender Deluxe may have a damaged power transformer. The original filter caps should have been charged decades ago -and more than once. They may work for a long time, but the service life is about 15 years and after that they can fail without warning. One issue that can occur when one fails is damage to the PT - I've several tweed PT's that burned out for exactly that reason. They are not parts that are changed because they fail - they are parts that are changed because of age.

    And FIW if a vintage amp sits unused for years the electrolytic caps usually crystallize fully or partially - there's no way to know, so general practice among techs around here is to recommend changing them in any amp that has not been powered up in over 5 years.

    Many filter caps have date codes that make it easy to check age; but I change undated ones in any amp 15+ years old unless there's documentation showing recent replacement.

    It sounds like the amps are not being serviced regularly, if at all. Tube amps are not designed to be played until they break - they need some parts replaced periodically. Filter and bias (in fixed bias) caps every 15 years or so and at the same time cathode bias caps and coupling caps tested and replaced as needed, voltage tests run (and records kept for future reference), noisy or off-spec resistors replaced, and pots & jacks cleaned and lubed. I always check for loose tube sockets and retension them as required when regular service is being performed.

    This is all normal "periodic service" work that is needed by all tube amps. It's no different than changing oil or tires on a car.

    IMO the Fender Deluxe needs to go to a qualified tech for service - have the other "normal" things checked out & serviced, the power tube cathode cap checked to electronic leakage, the bias checked and parts changed to adjust it if necessary, and - very important - have the power transformer tested, with it powered up for at least an hour to see if there's a heat related failure (obviously not that long if it shows signs of weakness/failure earlier).

    If the Victoria is close to 15 years old it's about time for it to be fully serviced as well - no matter how the caps look or test. Unfortunately, many techs only perform work as requested, so you have to specify filter cap replacement. It's one issue the amp manufacturers have sadly ignored IMO - they figure 15-20 years is past warranty so it's not their problem anyway.

    You mentioned that the tubes were checked, but as Wally mentioned a typical tube tester is pretty much useless.

    Common tube testers can only weed out bad tubes and test preamp tubes, but don't use high enough plate voltages to test the quality or comparative bias of power tubes. They also have to be calibrated every 5-10 years to even test preamp tubes. Otherwise, they are only good for weeding out defective tubes. Unless a tech has a high-voltage tester like a new one made by Orange, a custom-built one or one of the rare (and very expensive) military testers that supply amp-like high plate voltages "testing" is usually done by using a tube tester to check for shorts and gas leakage, and all other tests performed in an actual amplifier - checking voltages, the balance of the phase inverter and performing tests for microphonics.

    Good luck.
     

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