Tweet
Hi, first-time poster.
I've built a couple amps before, but I've never owned or even played a tweed. Built a Weber 5E5-A Tweed Pro clone with Heyboer transformers. It mostly works but there are a few problems. If this should be in another section let me know/move it.
Fender Schem:
http://music-electronics-forum.com/a...e5-a_schem.gif
Checked the voltages compared to the Fender schematic. The only one that was a concern was the cathode of the cathode-follower driving the tone stack, which was at 160V instead of 130V
Here are the problems/questions
1) Distortion starts at 3 on the volume knob with a P90-equipped guitar. Maybe this is normal? The distortion seems to come from the phase inverter. The PI grid is not very distorted, but it is quite distorted on the power tube grids. By 12 the distortion is crazy. I do have a 12AX7 in V2, as I only own one 12AY7 (which is in V1; the kit comes with all 12AX7s)
2) When the Bass control is turned all the way up, the volume cuts out almost entirely. Acts normal otherwise. Is this normal on a bass/treble knob tweed?
3) Oscillation when presence and tone controls are turned DOWN.
There is a serious ~16 KHz oscillation when the presence and tone controls are both turned down, when they are both around 2-3. The oscillation kicks in suddenly when turning either knob down, and then backs off gradually as the knobs are turned back up. They interact with each other; if one of them is higher, you have to turn the other lower to start the oscillation. It only happens when a speaker is connected, not with a resistive dummy load.
I've tried changing tubes, pushing the wires around, tried moving the OT leads around (did not swap them), tried running the treble-pot-wiper-to-grid wire away from the board and everything, but it always acts the same. Made sure the pots were the right value, checked board components /wiring a lot, can't figure it out. The treble pot and presence pot capacitors are grounded at the same joint on the brass plate, could this be the problem?
It goes away when the NFB wire is removed from the speaker jack.
Any thoughts/comments appreciated
I've built a couple amps before, but I've never owned or even played a tweed. Built a Weber 5E5-A Tweed Pro clone with Heyboer transformers. It mostly works but there are a few problems. If this should be in another section let me know/move it.
Fender Schem:
http://music-electronics-forum.com/a...e5-a_schem.gif
Checked the voltages compared to the Fender schematic. The only one that was a concern was the cathode of the cathode-follower driving the tone stack, which was at 160V instead of 130V
Here are the problems/questions
1) Distortion starts at 3 on the volume knob with a P90-equipped guitar. Maybe this is normal? The distortion seems to come from the phase inverter. The PI grid is not very distorted, but it is quite distorted on the power tube grids. By 12 the distortion is crazy. I do have a 12AX7 in V2, as I only own one 12AY7 (which is in V1; the kit comes with all 12AX7s)
2) When the Bass control is turned all the way up, the volume cuts out almost entirely. Acts normal otherwise. Is this normal on a bass/treble knob tweed?
3) Oscillation when presence and tone controls are turned DOWN.
There is a serious ~16 KHz oscillation when the presence and tone controls are both turned down, when they are both around 2-3. The oscillation kicks in suddenly when turning either knob down, and then backs off gradually as the knobs are turned back up. They interact with each other; if one of them is higher, you have to turn the other lower to start the oscillation. It only happens when a speaker is connected, not with a resistive dummy load.
I've tried changing tubes, pushing the wires around, tried moving the OT leads around (did not swap them), tried running the treble-pot-wiper-to-grid wire away from the board and everything, but it always acts the same. Made sure the pots were the right value, checked board components /wiring a lot, can't figure it out. The treble pot and presence pot capacitors are grounded at the same joint on the brass plate, could this be the problem?
It goes away when the NFB wire is removed from the speaker jack.
Any thoughts/comments appreciated
Comment