Hi,
I need to repair the guitar amp in the title. I'm new on tubes, it's the first time for me. Usually I repair keyboards.
After a time from 10 to 25 seconds about from power-on, the amp start randomly with one of the following issue:
-some intermittent little pop/cracking sounds on the speaker followed by a “uuuuuhmmmmm” continue sound
-a continue big big distorsion sound, like a big noise (with the volume and master to zero, see the video)
Yesterday I powered on the amp and all went well without crack sounds and with no audio distorsion for about 30 minutes. The sound was very good. I thought that the amp was repaired just moving the valves but I was wrong. Today the distorsion was back again.
Some notes:
-When the little crack sound appears, touching the first 3 gray ribbon cables (starting from left) with a plastic pencil, each touch is a crack sound on the speaker. The same on the EL84 valves.
-The first EL84 is immediately very very hot compared with the near one. The preamp valves are not hot.
I checked the diodes and are OK. To check the capacitors I have to remove the board.
Where I can start to do some measures?
One of the example above:
https://www.youtube.com/watch?v=kTSnM-uoD3k
Thanks a lot.
I need to repair the guitar amp in the title. I'm new on tubes, it's the first time for me. Usually I repair keyboards.
After a time from 10 to 25 seconds about from power-on, the amp start randomly with one of the following issue:
-some intermittent little pop/cracking sounds on the speaker followed by a “uuuuuhmmmmm” continue sound
-a continue big big distorsion sound, like a big noise (with the volume and master to zero, see the video)
Yesterday I powered on the amp and all went well without crack sounds and with no audio distorsion for about 30 minutes. The sound was very good. I thought that the amp was repaired just moving the valves but I was wrong. Today the distorsion was back again.
Some notes:
-When the little crack sound appears, touching the first 3 gray ribbon cables (starting from left) with a plastic pencil, each touch is a crack sound on the speaker. The same on the EL84 valves.
-The first EL84 is immediately very very hot compared with the near one. The preamp valves are not hot.
I checked the diodes and are OK. To check the capacitors I have to remove the board.
Where I can start to do some measures?
One of the example above:
https://www.youtube.com/watch?v=kTSnM-uoD3k
Thanks a lot.
Comment