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How do I know my amp has to be serviced?

Discussion in 'Glowing Bottle Tube Amp Forum' started by nosuch, Sep 3, 2017.

  1. nosuch

    nosuch Friend of Leo's

    Apr 4, 2008
    Hi Folks, in another thread I read that tube amps have to be serviced like every 10 or 15 years. Not only the power amp tubes should have to be changed but also some other parts.

    My Blues Jr. is like 10 or 12 years old now. I have the impression that lately it sounds a bit compressed and has less volume than it used to have.
    Time to change power amp tubes?
    Can i do this myself (what tubes would I have to buy?) or does it need to go to a tech?
    Also – given the age of the amp – is it time for a full service by a tech?

  2. Dacious

    Dacious Poster Extraordinaire

    Mar 16, 2003
    If it's never had tubes changed it may well require new ones depending on how much/loud it's been played.

    It would probably be prudent to get it checked out. A tech can fit new tubes and assess if the power filters and other electros are sound.

    If it's been played somewhat regularly and has no other issues it should be OK with a 'grease and oil change'.

  3. JD0x0

    JD0x0 Poster Extraordinaire

    Feb 22, 2009
    New York
    You wont always know. An amp can have major issues going on and sound amazing.

    Based on the age of your amp, it may also be time for new electrolytic caps. Resistors should be checked for heat stress, too.
    Cam likes this.

  4. Milspec

    Milspec Tele-Afflicted

    Feb 15, 2016
    It might need a cap job and it might not depending on how much it has been played and pushed. It is sort of like mileage on a car more than age these days. Could also just be your power tubes dying.

    A Blues Jr. has a fixed bias, so you don't need to worry about having to adjust anything when you change the tubes. Buy a set of JJ tubes and replace the tubes and see what you have. It might just be as simple as that.

    If you choose to take it to the tech, it will cost you new tubes anyway, so start there yourself and see what happens. If things don't recover from the tube change, then take to be serviced. You will already have the tubes, so you will be out nothing at that point and keep the old ones as spares.

  5. nosuch

    nosuch Friend of Leo's

    Apr 4, 2008
    Oh I play it a lot – at home, small gigs, in the studio. I think I'll take it to a tech after next weeks gigs.

  6. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

    Mar 2, 2003
    Lawndale CA
    As mentioned it likely needs new power and driver tubes. When those are replaced the amp should have the bias checked at minimum and likely adjusted.

    Electrolytic filter caps have a service life of appx 15 years, so you're right on the edge. You could have it done now while it's at a tech for the bias adjustment or you should be safe for a few years. It's unusual for caps to fail right at 15 years and they usually go longer - but as they get older there's nmore of a chance of failure, so the idea is to get the work done before then. Failure can cause very expensive damage to other parts. It's not common but it happens enough that it's wise to get it taken care of. That work *generally* runs $100-200. Don't quote me - if extra work is involved it can be more and some techs charge more for work on PCB amps.

    If you talk to a tech don't have him just "check" the caps, as caps about to frail often check out fine. Either get the electrolytic filter and bias cap replacement done or don't (plus bypass caps if the test bad - those undergo less strain, don't damage things if they fail and are usually replaced only when they test bad) .

    I strongly recommend getting it done within the next few years as those amps usually don't have the best parts to begin with. Glad you are thinking about it though!

  7. thickwood

    thickwood TDPRI Member

    Dec 6, 2011
    hampton virginia
    Replace power tubes now and phase inverter and the best tube in my opinion is a balanced sovtek 12ax7 lps
    long plate special and chords hold together under heavy clipping overdrive when other PI tubes turn OD into garbage !
    Tungsol 12ax7 tubes in the other 2 sockets are good !

    Get matched power tubes with a plate current reading of at least 32 milliamp and sturdy tough tubes JJ or Sovtek are good and cheap.
    I have a set of el84 gold lion tubes that sound good but my other sovtek el84 tubes sound similar !

    Do not let a eager tech guy start replacing caps if you have no problem !


    MMARSH Tele-Meister

    Jun 21, 2015
    Here's a clue:

  9. thegeezer

    thegeezer Tele-Holic Gold Supporter

    Jul 5, 2010
    West Michigan
    Silverface is right but I'm of the run them until they sound funny school of thought. It took about 30 years the first time for my Twin Reverb to need service (it's 43 years old now and sounding a little off again). Tubes? When they go bad. The RCAs in my Twin Reverb still test well and sound great.

    My '54 Deluxe was re-capped shortly before I bought it, five or six years ago. A couple of the Astron bias caps are still in it. I swapped out the modern TAD power tubes for some GE 6v6s I had but the 5y3, 12ay7 and 12ax7 are RCAs of unkown age and hours of use.

    I'm sure a good going over once in a while optimizes amp performance but you know what they say: your amp always sounds best right before it blows up;)
    Fiesta Red likes this.

  10. ranjam

    ranjam Tele-Holic

    Dec 29, 2015
    Big difference. YOUR amplifiers are from a time when Fender knew what the f@ck they were doing, as did RCA. Now? :lol:
    The Blues Junior has no bias control, is almost always biased hot, and the Russian tubes aren't noted for lasting like your RCAs. It's the reality.
    thegeezer and SnidelyWhiplash like this.

  11. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Fender bought a truckload of really crappy Illinois Caps years ago, and some of them have shown a really short service life - as short as 5 to 7 years in some HRDlx amps.

    I'm with Silverface here. You're at the short end of the typical service window, and aging caps and tubes can make an amp sound anemic.

    If you can spare the amp and money for the service call, go for it. It's preventative maintenance, and will keep your amp running strong for another 15-20 years, minus tube changes.

  12. Frank'n'censed

    Frank'n'censed Doctor of Teleocity

    Mar 27, 2011
    Parts Unknown
    "How do I know my amp has to be serviced?"

    When it no longer services you
    Big tuna likes this.

  13. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

    Mar 2, 2003
    Lawndale CA
    Dude, you owe me for a T-shirt, carpet cleaning...and for the pain & suffering when hot coffee shot out of my nostrils!

    Big tuna likes this.

  14. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

    Mar 2, 2003
    Lawndale CA
    And how should an amp neophyte like the OP determine that? Or even know what it is? Should he look on the box? Ask the GC clerk?

    Big tuna likes this.

  15. muudcat

    muudcat Tele-Holic

    Jan 3, 2010
    Fountain City, Wi
    I get tubes from Dougs Tubes and he measures the plate current and writes it on the tube box

  16. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

    Mar 2, 2003
    Lawndale CA
    Honestly, I've never heard of Doug's Tubes. I'd wager most buy tubes either from major sellers like,, etc online or at local retailers. Places like GC and guitar stores don't have that info and online sellers don't list "current readings" - because it's a subjective number that is only meaningful in some sort of context. Example - "32ma" at what plate voltage - and in what amp? Because that would be a specific bias setting at a specific plate voltage that might or might not sound good in a specific amp. It's not a "tube measurement".

    Interestingly I just looked up "Doug's Tubes". none of his listings appear to have any such "current readings". So do you know what he's actually selling you?
    Nickfl likes this.

  17. MMARSH

    MMARSH Tele-Meister

    Jun 21, 2015
    So sorry, send the bill please! I've seen those pics around the net and that it might be a funny :) not that the op's post doesn't deserve a serious answer, though...which you eloquently gave!
    Silverface likes this.

  18. Sweet Lou 275

    Sweet Lou 275 Tele-Meister

    Nov 24, 2016
    My experience is usually the preamp tubes wear a little faster. Power tubes usually last a bit longer without really affecting tone or volume much. You can swap the preamps easily and see if it helps. If they're original they need done anyway. If you play it somewhat regular, you really shouldn't be getting 10-12 years out of your tubes. Definitely take it to someone who knows what they're doing. Incorrect bias kills tubes and more. Tubes and a decent tech are much cheaper than new transformers. Opinions will vary, and I do have some amps with very old tubes, but I check them regularly and don't play on them much. Definitely might need a cap job, but I'm not familiar with the quality of the components Fender used then.

  19. Indian Joe

    Indian Joe Tele-Meister

    May 21, 2017
    Ramona, California, U$A
    Those amps MMARSH posted pics of look about like some amps I had to play thru as a teen, maybe better! No wonder I sounded so bad on that 2-p/u Kay. Played a big pow-wow up in Quebec c.1971 and a guitar player had an amp looking about like the Fender in the pic, no-name, fiber-board guitar, somehow he sounded amazing. Must have been the smoke in the air....

  20. DaveKS

    DaveKS Friend of Leo's

    Oct 21, 2013

    Sorry but no. In BJ with reg use you can expect to burn through a set of el84 every 3yrs max, el84 are the Bic lighters of power tubes. Preamp tubes should be good for about 5-7yrs.

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