Hey mates, I'm in need of some ideas to debug my Laney TI-15...
It's been a while that I'm perceiving that, eventually, it begins to oscilate de output 'til it stops the sound... after a while without any output (which varies time to time), it starts to work again, oscilating 'til it reaches the normal operation point!
I'm not an expert, but in spite never had worked directly, I have some knowledge about tube circuits (studied it by myself during my EE graduation)... I have analyze superficially, and here are some points I observed:
- the amplifier turns on, with status lights working normally, without oscilation;
- the fuse presented no problems;
- the tone, when the amplifier is working normally, comes unaffected (so, I believe that the EL84's still have some life span);
- the filaments seems to be fed normally (I can't see the preamp tubes because of the metalic shields, but the power tubes cathodes lights, meaning that the cathodes' wiring is operational);
- never used the amplifier above half of its full power (5 was the max during a 2h gig);
- when the amplifier oscilates and turns down the volume, if I start to open the master volume, it presents some audible sounds (not the full output, but loud enough to bother the neighbor).
I didn't do a test that could help me with the debugging, but I'll do it the next time it happens: use the phone output, to see if it continues (what could help me point where in the circuit the problem could be).
The tubes was the original Ruby's, but I changed the entire preamp for JJ's as the first test of the debugging... another thing to say is that this amplifier is made in the "newer standard", full of SMDs (which I'm not experienced with)!
Thanks in advance!
Cheers
It's been a while that I'm perceiving that, eventually, it begins to oscilate de output 'til it stops the sound... after a while without any output (which varies time to time), it starts to work again, oscilating 'til it reaches the normal operation point!
I'm not an expert, but in spite never had worked directly, I have some knowledge about tube circuits (studied it by myself during my EE graduation)... I have analyze superficially, and here are some points I observed:
- the amplifier turns on, with status lights working normally, without oscilation;
- the fuse presented no problems;
- the tone, when the amplifier is working normally, comes unaffected (so, I believe that the EL84's still have some life span);
- the filaments seems to be fed normally (I can't see the preamp tubes because of the metalic shields, but the power tubes cathodes lights, meaning that the cathodes' wiring is operational);
- never used the amplifier above half of its full power (5 was the max during a 2h gig);
- when the amplifier oscilates and turns down the volume, if I start to open the master volume, it presents some audible sounds (not the full output, but loud enough to bother the neighbor).
I didn't do a test that could help me with the debugging, but I'll do it the next time it happens: use the phone output, to see if it continues (what could help me point where in the circuit the problem could be).
The tubes was the original Ruby's, but I changed the entire preamp for JJ's as the first test of the debugging... another thing to say is that this amplifier is made in the "newer standard", full of SMDs (which I'm not experienced with)!
Thanks in advance!
Cheers
The output transformers are a known issue. They have intermittent short circuit primaries.
Here is a link for a replacement;
Valve Transformer VT1576
Here is a link for a replacement;
Valve Transformer VT1576
My mistake, mate! Didn't payed the necessary attention... is there any way to transfer this thread to there?
Didn't know that this amplifier had a buged output tranny... thanks for the answer!
Just click on the red warning triangle at the bottom left of your post and ask a Mod to move it. They are quite friendly!
- Status
- Not open for further replies.