The Hughes & Kettner User Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.
The Hughes & Kettner User Forum

The Unofficial guitar amp and cabinets forum for users of Hughes and Kettner products. We are not affiliated with Hughes and Kettner!!


3 posters

    TM20 Deluxe dropping volume

    Pankow
    Pankow


    Posts : 2
    Join date : 2021-03-28

    TM20 Deluxe dropping volume Empty TM20 Deluxe dropping volume

    Post by Pankow Thu Apr 08, 2021 6:42 pm

    After a few minutes of playing, my volume drops dramatically. Sometimes it comes back. TCS doesn't show any issues with the power tubes. Preamp tubes were replaced last week but the problem was happening before then and still persists. I changed the preamp tubes to improve the sound which they did nicely
    smurf211
    smurf211


    Posts : 9
    Join date : 2017-12-27

    TM20 Deluxe dropping volume Empty Re: TM20 Deluxe dropping volume

    Post by smurf211 Sat Apr 10, 2021 8:57 am

    Edited hadn't had my coffee yet: Check you power, hopefully running through a filtered power rack, something similar to a Furman, they help filter and somewhat regulate the ac your plugged into. Surge suppressor would help in the interim but it may be an issue with you ac fluctuating. I have an UPS in my studio for all of my protools equip and I can see the ac vary occasionally. Of course if it get s to be too much I stop and save everything and check the weather make sure there isn't a thunderstorm in the area. 2c -hth


    Last edited by smurf211 on Sun Apr 11, 2021 9:01 am; edited 1 time in total
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    TM20 Deluxe dropping volume Empty Re: TM20 Deluxe dropping volume

    Post by bordonbert Sat Apr 10, 2021 9:41 am

    This does sound like it should be a valve problem but that isn't cast in stone.  I notice you did mention that the problem was there before putting in new preamp valves which should rule that out.  There are one or two other things you can try and there is a sensible set of simple tests to perform to start getting to grips with what is the problem.

    First, take a jack plug and short out its contacts then plug it into the Loop Return socket.  A signal lead with the other end shorted with a bit of wire will do.  The signal chain is passed through the switch wafers of this socket.  I don't mean the contact area of the plug and the socket, I mean the side switch which is opened when a plug is inserted.  These do occasionally corrode in any amp with a loop wired like this.  Putting the jack plug in simply bypasses those switch wafers and should clear up any problem of this type.  If it does you know you only have to clean the switch contacts of the socket.

    Second, feed a signal into the Loop Return from another amp's Loop Send.  If the volume is stable then the problem isn't in the power amp stage which rules out the output valves and V2b (T2b) the phase inverter.  (The TM only has a single triode set up as a Cathodyne Phase Inverter rather than the two triode Long Tailed Pair which its big brothers have.)

    Third, feed the TM20's Loop Send into the Loop Return of another amp and check out the preamp in the same way.  This will show whether V1 (T1) or V2a (T2a) are the culprits.

    If you don't have a second amp with which you can do this then swap in one of your old 12AX7s for each of V1 and V2 one at a time in turn.  If you don't have a spare valve you can even swap the two preamp valves around inside and just see if the nature of the problem changes. Make sure to swap them back to their original positions after testing.  Swapping the output valves will achieve nothing in the 20W amps as they only have a single pair and the fault is just swapped from one side of the signal to the other which is pretty much inaudible in most cases.



    Try these simple tests and let us know what you find.  (My money is currently on the Loop Return socket being the culprit.)


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    smurf211
    smurf211


    Posts : 9
    Join date : 2017-12-27

    TM20 Deluxe dropping volume Empty Re: TM20 Deluxe dropping volume

    Post by smurf211 Sun Apr 11, 2021 9:04 am

    Mr. BB thanks for the heads up. Morning fog I guess, anyway, great troubleshooting scheme, don't know if the OP has the equipment available to perform the tests but still your methodology is definitely sound.
    Rsp/
    -sm
    Pankow
    Pankow


    Posts : 2
    Join date : 2021-03-28

    TM20 Deluxe dropping volume Empty Re: TM20 Deluxe dropping volume

    Post by Pankow Sat Apr 17, 2021 7:11 am

    Changed the power tubes.  problem solved. Mine is a simple setup. Just an amp and a speaker cabinet. No UPS, no spare amps
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    TM20 Deluxe dropping volume Empty Re: TM20 Deluxe dropping volume

    Post by bordonbert Sat Apr 17, 2021 5:42 pm

    Hahaha! In my own defence I did say "This does sound like it should be a valve problem but that isn't cast in stone." So it was all along. Good to remember those simple tests though. With just a guitar cable and another amp, (don't we all have a muso friend?), or by replacing with an old valve or swapping the valves around carefully you can tie down the problem to which part of the amp it is and even identify a duff preamp valve without any test gear or expensive "guru intervention". Especially remember the Loop Socket problem. That one appears regularly all over the music web.

    Glad it was fixed so easily. Enjoy the relief of playing as normal, even if you can't do anything else as normal nowadays. Very Happy


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie
    smurf211
    smurf211


    Posts : 9
    Join date : 2017-12-27

    TM20 Deluxe dropping volume Empty Re: TM20 Deluxe dropping volume

    Post by smurf211 Thu Apr 22, 2021 5:41 am

    The UPS is on my Protools PC, I check it occasionally for power status. All of my amps and other gear are filtered with a stable power distribution units.

    Glad you got it sorted. Usually when I change tubes I change all of them and keep the old ones for spares. Just a thought.
    bordonbert
    bordonbert


    Posts : 1772
    Join date : 2015-01-28
    Age : 72
    Location : Southern England

    TM20 Deluxe dropping volume Empty Re: TM20 Deluxe dropping volume

    Post by bordonbert Thu Apr 22, 2021 7:21 am

    I can see where you are coming from there Smurf.  I take a different view myself based on a career in electronics design.  I'll generally keep a set of brand new spares and keep on using the ones I have in the amp until there is a reason to change them.  After all they are the ones giving me my current sound which I am presumably happy with.

    Preamp valves do not "wear out" as most people think they do.  The internet is an appalling source of electronics misinformation, everyone is an expert just by repeating things they have heard from others who are also just repeating them and so on.  You should get many thousands of hours of use out of a decent 12AX7 in a good circuit design.  In a well designed stage even under heavy overdrive preamp valves are running under no stress.  When they eventually go they go and you know it.  Power amp valves do go soft earlier but even so you get lots of life out of them if you treat them sensibly.

    Of course that is most definitely "in a well designed stage" and there are some around which are anything but that.    And don't get me started on the crap talked about electrolytic capacitors and how bad they are...


    _________________
    Newcastle Brown, can sure smack you down
    You take a greasy wh*re, and a rollin' dance floor
    You know you're jailhouse bound!

    Rock On Humble Pie

    Sponsored content


    TM20 Deluxe dropping volume Empty Re: TM20 Deluxe dropping volume

    Post by Sponsored content


      Current date/time is Thu Mar 28, 2024 3:39 pm