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!!


    Output dropped to near nothing but I can hear faintly. Tubes ?

    Share
    avatar
    John_M

    Posts : 22
    Join date : 2016-03-11
    Location : New England

    Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by John_M on Tue Sep 13, 2016 7:58 pm

    Gents. So I guess it was inevitable. Sunday I fired up the GM36 after 2 gigs, sounded great. Same as always. Just fired it up (touched nothing since) and now the sound is faint. If I crank the master I can hear it louder but still faintly. Output tubes? Tried cycling the power a few times. Still the same.
    avatar
    namklak

    Posts : 185
    Join date : 2015-01-30
    Location : Denver, CO

    Re: Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by namklak on Tue Sep 13, 2016 10:54 pm

    John_M, I saw you posted in the other thread and I admit your data mixed with the other guy's data confused me.  Please post here what you have tried, with results?
    I believe you said you swapped EL84s with no help.  
    Guitar with overdrive box with some gain into fx return with FX loop engaged?
    Do you have another amp?  Can you take the GM36 fx send and connect it to the fx return of another amp?
    Got any spare 12AX7s?
    Did you buy it from GC in the last 45 days?

    Edit: what does TSC report on the output section?
    avatar
    John_M

    Posts : 22
    Join date : 2016-03-11
    Location : New England

    Re: Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by John_M on Wed Sep 14, 2016 6:36 am

    Sorry and thanks for the response. I started this thread, did searches and then found that thread which had similar symptoms, so I posted there - sorry for the confusion. I will have to test the send and return as you stated. I replaced all the power tubes. No help. Will do the preamp later tonight.  - -I have an old Zoom G2 that I can run direct into the return. The TSC did some flashing things, but I didn't record the sequence so I will have to get back to you all here. I contact H&K on FB and they were super quick to respond and point me to Yorkville in NY to find a tech if need be. Bummed because on Sunday I was literally thinking how fantastic this amp has been and how great it sounds. Oh well, things happen.

    So far -
    • Turned up master - can hear the channels and all are consistent, just about 1% of the normal volume, so clean is clean, all dirts are consistent, FX loop is audible, and built in FX are as well.
    • ran guitar direct into the return - nothing. Not sure what I was thinking, obvi need a preamp but seems like the other thread did this and it worked so gave it a shot.
    • replaced all the power tubes, same result
    • changed speaker cables same result
    • went direct to amp, jumpered FX loop - same result
    avatar
    bordonbert

    Posts : 815
    Join date : 2015-01-28
    Age : 97
    Location : Southern England

    Re: Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by bordonbert on Wed Sep 14, 2016 9:10 am

    Duuuhhh! Confused me too Namklak. I just posted there and then found this. Still, no worries now.

    In your case John_M you took the right action. Running a signal into the Fx Return checks out the power amp stages in isolation from all of the preamp circuitry. If you genuinely get absolutely nothing then your problem is there. You could also try taking the signal out of the Fx Send and treating that as an input to another amp's Fx Return if you have one available. I would think you would find that the amp works fine in that way which would prove there is nothing wrong with the preamp stages.

    Have you tried swapping out the Phase Splitter/Inverter valve V3? That's the 12AX7 on the opposite end to the metal can shielded one. This is configured so it would affect both sides of the output stage. If you don't have a spare 12AX7 at hand then swap it out with the 12AX7 next to it in V2, (you need to be specific about which one so you can replace them in the same sockets!), and retest with a signal into the Fx Return socket. If it is that PI valve at fault it should then give an output. Even if it still doesn't work replace the valves in their original order afterwards.
    avatar
    John_M

    Posts : 22
    Join date : 2016-03-11
    Location : New England

    Re: Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by John_M on Wed Sep 14, 2016 9:58 am

    thank you bordonbert - I have not tried the 12ax7s. I will tonight and report back - here's hoping!
    avatar
    John_M

    Posts : 22
    Join date : 2016-03-11
    Location : New England

    Re: Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by John_M on Wed Sep 14, 2016 7:34 pm

    That was it!!!!!! The PI must have flamed out. New JJ in there and BOOM! Bordonbert, Namklak- pm me your shipping addresses and I will send a care package along. So happy this amp is still going. Love this thing!
    avatar
    namklak

    Posts : 185
    Join date : 2015-01-30
    Location : Denver, CO

    Re: Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by namklak on Wed Sep 14, 2016 8:53 pm

    No need for a care package, but if you are in Denver, you can buy me a coffee or beer.  Or come see my band.  I owe bordonbert many beers/coffees, but a few miles and some water are probably keeping that from happening.

    On a side note, this debugging is fun and good.  But the tubes are the only user-serviceable parts.  Realistically, it anything goes wrong, swap the tubes.  If that doesn't fix it, it really doesn't matter what the problem is, off to the shop it goes.   No matter what tube amp you own, you should own a set of output tubes, and some pre-amp tubes. Tubes are cheap and are almost brainless to swap, especially on a self-biasing amp like the GM.
    My $.02
    avatar
    bordonbert

    Posts : 815
    Join date : 2015-01-28
    Age : 97
    Location : Southern England

    Re: Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by bordonbert on Thu Sep 15, 2016 5:43 am

    I'm with you on all of that Namklak. The valves are a no-brainer to check and having a set on hand as spares makes absolute sense. (Now where did I leave mine? I must put them in the gigbag. Embarassed ) There are a couple of things I would also say could be tackled by someone with genuine experience but they are few and far between and are more mechanical than electronic. As I said, for my money Namklak is spot on though, in a highly compact PCB based amp with major digital portions based on SMD devices you are up against it in repairing at the component level. Most guitar techs are nowadays reduced to board replacement as the only way they can fix things in amps like this. The upside of that is that it doesn't take them too long to complete a repair, the downside is that the manufacturers can charge what they like for a replacement board. I'm lucky, nowadays I have the time and the curiosity to look into stuff for the sake of it but they don't, being on the clock in their work.

    As to the coffee/beer.... I like a beer but have been known to imbibe nature's nectar, an ouzo, in hot weather. I'll make sure to raise my glass on your behalf (later today). drunken Do stick around and get used to us here, we're really a genuinely nice group without too much ego and the advice you get from the likes of Hwystar, Namklak, Voodoo Jeff and the rest of us is honest, from personal experience or technical correctness and bullshit free. We weed out the bullshitters pretty quickly so what you are told will really have merit and be worth considering. There's a lot you can contribute from your own playing with the GM too which we can all benefit from.
    avatar
    John_M

    Posts : 22
    Join date : 2016-03-11
    Location : New England

    Re: Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by John_M on Thu Sep 15, 2016 3:11 pm

    yeah - I guess I should have just changed all the tubes and see if that did it, since it was all I could really do anyway. I bought this used off the interweb so it would likely be off to Niagra Falls, or wherever they told me to send it local to me. Good to know that symptom = PI issue. Hope these old matched set of GT EL84s are still good that I put in there. Didn't get to really put it thru its paces last night, son was sick asleep upstairs so only could check for a few seconds.
    avatar
    John_M

    Posts : 22
    Join date : 2016-03-11
    Location : New England

    Re: Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by John_M on Mon Sep 19, 2016 12:20 pm

    So got the new JJ set coming soon. Funny that a couple days later, my Crunch and ultra channels went quiet. Replaced the other 2 12AX7s and all is well. Once the JJ kit gets here will replace all the tubes with those.

    Sponsored content

    Re: Output dropped to near nothing but I can hear faintly. Tubes ?

    Post by Sponsored content


      Current date/time is Wed Nov 22, 2017 2:37 am