Dumble problem
Moderators: pompeiisneaks, Colossal
Re: Dumble problem
I'm willing to take a look at it, but distance...
Re: Dumble problem
So a friend borrowed your amp? And he played with it on his own for a while? Or where you present?
Is your Output Transformer secondary switched appropriate? For instance an 8 ohm speaker to the 8 ohm load? When your amp is on 4 ohm into an 8 ohm load you get a smoother sound. But please make sure it's not on the 16 ohm setting into a speaker with a lower load.
I have never heard of overdrive/boost pedals that can break down an amp. If you know how to check voltages, I presume you also know how to check the value of resistors? You can check the NFB resistor (as all the resistors) for all the values. You can also put your Digital Multimeter (DMM) on the lowest ohm setting (200 ohm's usually) and check for continuity (you can check then if connections are solid or if there is extra resistance added. usually the DMM adds a bit of resistance on its own which you can measure by putting the red and black together).
It would help if you post some results of the voltages (Plates on the end tubes, across the dropping resistors, and the anodes on the preamp tubes both before and after the anode resistors) Set the DMM on maximum DCV, put the black lead on the chassis (I usually put it in a screw hole) and then put the red lead with your RIGHT HAND on the appropriate spots. Might as well read the wall voltage as well as that might explain possible lower voltages (set the DMM on 750AC)
If all is correcto, then you can start reflowing solder joints that look suspicious. (If you know your way with the soldering Iron).
It is always possible that leads came loose or break off due to traveling and vibrations. Another possibility could be faulty preamp tubes, but then you usually would have a squeel or hum.
Veel succes!
Is your Output Transformer secondary switched appropriate? For instance an 8 ohm speaker to the 8 ohm load? When your amp is on 4 ohm into an 8 ohm load you get a smoother sound. But please make sure it's not on the 16 ohm setting into a speaker with a lower load.
I have never heard of overdrive/boost pedals that can break down an amp. If you know how to check voltages, I presume you also know how to check the value of resistors? You can check the NFB resistor (as all the resistors) for all the values. You can also put your Digital Multimeter (DMM) on the lowest ohm setting (200 ohm's usually) and check for continuity (you can check then if connections are solid or if there is extra resistance added. usually the DMM adds a bit of resistance on its own which you can measure by putting the red and black together).
It would help if you post some results of the voltages (Plates on the end tubes, across the dropping resistors, and the anodes on the preamp tubes both before and after the anode resistors) Set the DMM on maximum DCV, put the black lead on the chassis (I usually put it in a screw hole) and then put the red lead with your RIGHT HAND on the appropriate spots. Might as well read the wall voltage as well as that might explain possible lower voltages (set the DMM on 750AC)
If all is correcto, then you can start reflowing solder joints that look suspicious. (If you know your way with the soldering Iron).
It is always possible that leads came loose or break off due to traveling and vibrations. Another possibility could be faulty preamp tubes, but then you usually would have a squeel or hum.
Veel succes!
Re: Dumble problem
Thanks for your offer Erwin, it is quite a distance.
Thanks Kassie for your explanation, I guess this is also usefull for others that have amp problems. Coming weekend I have some time again to check things. I did measure a lot already, all voltages are OK ( exactly as when the amp was working perfect ) and I checked almost all resistors and they were also OK. I do hope I did not wreck the OT.
Is there a guide to check transformers? I did read something about that long ago, but seemed very difficult and was from just one source.
Thanks Kassie for your explanation, I guess this is also usefull for others that have amp problems. Coming weekend I have some time again to check things. I did measure a lot already, all voltages are OK ( exactly as when the amp was working perfect ) and I checked almost all resistors and they were also OK. I do hope I did not wreck the OT.
Is there a guide to check transformers? I did read something about that long ago, but seemed very difficult and was from just one source.
Re: Dumble problem
Thank you Kassi for the link!
Very usefull info how to test a OT.
Best
Hans-Jörg
Very usefull info how to test a OT.
Best
Hans-Jörg