Second build issue

[lpd]

Ok I have sorted out my voltage issue on my amp and have a pt on order but I noticed with guitar at 3 on bridge (les paul) I get feedback and a note that crackles afterwards on the g and b strings it sounds like the cone is crackling or rattling after I hit a note on the g or b string very noticeable on the g. If I hit notes on the d string above 9th fret same issue. Higher frequencies cause a rattle tone in my speaker.

I've rolled tubes and tried different guitars and speakers. So I'm certain it's inherant in the circuit. Thoughts of where to start looking?

[geetarpicker]

It howls with the guitar on 3, but does it then stop if you turn off the guitar?
Last week a thread on an Express that howled went nuclear...so we need more info here for sure...

Potted pickups are just about required with these amps, and just because the pickups may have come potted doesn't mean they are potted well enough and may need to be done again. If your humbuckers have covers the pickups may need to be potted with the covers on also.

A very non musical breakup on all notes when playing clean sounds like the amp is self oscillating. Might need some pics to go further there with perhaps lead dress suggestions. Also some builds may not be stable at all without a bottom ground plate, but some are ok without it.

You may have to go through a BUNCH of preamp tubes to find ones that work well. That said, if you DO NOT stack the amp on the cab the preamp tubes will be much less finicky. I've even seen output tubes go microphonic in TW builds and even vintage Marshalls so don't rule that out also. Typically though, output tubes that go microphonic ring at a much lower howl than preamp tubes which can be more of a screech.

[lpd]

It howls with the guitar on 3, but does it then stop if you turn off the guitar?
Last week a thread on an Express that howled went nuclear...so we need more info here for sure...

Potted pickups are just about required with these amps, and just because the pickups may have come potted doesn't mean they are potted well enough and may need to be done again. If your humbuckers have covers the pickups may need to be potted with the covers on also.

A very non musical breakup on all notes when playing clean sounds like the amp is self oscillating. Might need some pics to go further there with perhaps lead dress suggestions. Also some builds may not be stable at all without a bottom ground plate, but some are ok without it.
You may have to go through a BUNCH of preamp tubes to find ones that work well. That said, if you DO NOT stack the amp on the cab the preamp tubes will be much less finicky. I've even seen output tubes go microphonic in TW builds and even vintage Marshalls so don't rule that out also. Typically though, output tubes that go microphonic ring at a much lower howl than preamp tubes which can be more of a screech.

Sorry it's more of a buzz that rings through the speaker the higher up I go on the neck the worse it gets where you can't hear the note at all. Just a buzz/cone rattle (kind of like a blown voice coil rattle for reference on sound) I've tried different cabs and guitars rolled tubes with no avail. I'm sure it's the circuit. It was put into a traynor head and not exact same dress lead. The howl was a microphonic tube I replaced. I will post a pic open to feedback. On bridge dined it's psychotic. Lots of controllable feedback. The problem I have is clean. Volume on three/four. Lower volume sounds starved and thin. At three it's got lots of texture but there is some sort of issue on higher frequencies. Pics to follow.

[geetarpicker]

Kind of sound like an oscillation issue. I've heard problematic amps that would oscillate at such a high frequency that it was above the range of hearing so you wouldn't even hear a noticeable squeal. What you would hear however was your cleans would be really thinned out and garbled, as the high frequency would saturate the OT tubes and OT and would make the amp always sound dirty no matter how far you backed the guitar down. One check for this is to look at the output tubes in a dark room. With the amp in play mode see how much blue glow each power tube has, then turn it up a bit (without playing) and see if this blue glow really get's brighter. Anyway, you are looking for signs that the output stage is actually running away into clipping (without a guitar signal) and is really pushing the output tubes, even if it isn't audible to anyone....except nearby dogs. Hmmm...Hey Rover!

[lpd]

Kind of sound like an oscillation issue. I've heard problematic amps that would oscillate at such a high frequency that it was above the range of hearing so you wouldn't even hear a noticeable squeal. What you would hear however was your cleans would be really thinned out and garbled, as the high frequency would saturate the OT tubes and OT and would make the amp always sound dirty no matter how far you backed the guitar down. One check for this is to look at the output tube in a dark room. With the amp in play mode see how much blue glow each power tube has, then turn it up a bit (without playing) and see if this blue glow really get's brighter. Anyway, you are looking for signs that the output stage is actually running away into clipping and really pushing the output tubes, even if it isn't audible to anyone except nearby dogs... Hey Rover, listen to this!

Haha thanks. I appreciate the insight. I have an extra diode on the output tubes for fly back not sure what impact that has overall but I will darken the room and experiment. Btw I use your clips as a benchmark for tones I'm after sans 1959 les paul and original wreck :/ I really dig the warmth you get on a bridge clean with your LP on your wreck. Mine is a bit bright lots of chime even with darker character tubes.

[lpd]

Not exact to kens layout but a good start.


[IMG:768:1024]http://i796.photobucket.com/albums/yy247/jeeping/photo1_zps216e9a41.jpg[/img]

[lpd]

Ok I cleaned up the output section a little. I had this built for me by a local hifi builder, but wasn't too thrilled with some of the dress leads ect. I pulled the diodes and pulled one, now I have three, and strapped to the octal socket, which was grounded to the same point as the bias ground...should these be separate? I also cleaned up the dress leads of the resistor to the power supply for b+ on the outputs.

I am curious should I ground the flybacks to a separate point? Also wondering if I should separate the grounds on the power supply ie: B1/B2/B3/B4/B5? I've noticed the B1 is grounded on the chassis but also strung onto B2 preamp filtering. Is two grounds necessary?

Now I have clean notes on clean guitar volume at 3-5 (at 5 its starts to break up but much smoother and doesn't drown the notes), but now have a ghost or buzz note on each note, mostly noticed on the g string and a notes especially past the 12th fret I get feedback on a notes guitar volume at 3-4.

Any ideas are welcomed.

[geetarpicker]

It is hard to say if you will ever get the amp to behave with such a different lead dress, layout, and longer lead length just about everywhere.

Still... as long as you are totally sure the feedback and issues you describe are not simply natural note feedback, or loose pickups winds (needing more extensive potting) I'd try one other thing. Get the amp playing and acting up on the bench where you can access the circuit, maybe have someone else play the guitar. Make sure you follow all common sense about the high voltages, but the take a wood drums stick and poke around at some of the wires. You may find moving some wires slightly may seem to change the feedback issues when you push them (worse, less, different frequency, etc) and that might at least localize where you may need to work on lead dress. Be careful, and only try this with a non-metallic object like a chop stick or drum stick. To be extra careful you could keep one hand in your pocket while poking around in the amp.

It's always hard when someone builds one of these amps with a totally different layout and lead dress. You are then in uncharted territory, but you might get lucky and figure it out.

[lpd]

It is hard to say if you will ever get the amp to behave with such a different lead dress, layout, and longer lead length just about everywhere.

Still... as long as you are totally sure the feedback and issues you describe are not simply natural note feedback, or loose pickups winds (needing more extensive potting) I'd try one other thing. Get the amp playing and acting up on the bench where you can access the circuit, maybe have someone else play the guitar. Make sure you follow all common sense about the high voltages, but the take a wood drums stick and poke around at some of the wires. You may find moving some wires slightly may seem to change the feedback issues when you push them (worse, less, different frequency, etc) and that might at least localize where you may need to work on lead dress. Be careful, and only try this with a non-metallic object like a chop stick or drum stick. To be extra careful you could keep one hand in your pocket while poking around in the amp.

It's always hard when someone builds one of these amps with a totally different layout and lead dress. You are then in uncharted territory, but you might get lucky and figure it out.

Yep it's not at all the same in layout :-/ I have managed to remove some of the noise issues but can seem to squeeze much clean out of it. Could be a combo of lower voltages (about 40 volts each stage) and a 5.2k transformer.