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H folks, this week I have been working on a 5F2A clone that I built a few years ago. I recently did some work. I replaced a few resistors that had been overheated when originally installed. They had signs of cracking and I found them chirping when I did a chopstick test. I replaced with same values. I also added some Zener diodes to get the voltage down to vintage schematic values. That all seemed to work as I am at a steady 364V B+ now.
When I fire up the amp now, the amp makes noise with a guitar but it's quiet. It almost sounds like the OT signal is grounded or something. I have been racking my brain for hours over this symptom. Trying different things to no avail. I have got myself worked stupid over it and need to take a break and a fresh new look after a rest.
I've tried swapping in known good tubes.
Lifted board several times to look underneath and inspect & check wiring
Checked and rechecked all wiring many, many times.
I replaced 2 coupling caps and the 2 cathode caps.
Checked all my contacts for grounds or not as required.
I have tried different speakers and cords and guitars to eliminate those variables
Chopstick entire circuit when on, it's all nice and quiet
I have switchable NFB. I hear a little crackle when I switch it on and off. Same as before. I also removed NFB completely to eliminate that option. No improvement.
I lifted board and tested amp. To make sure nothing under the board was touching ground. No improvement.
Tone and volume knobs work as they should.
Just the amp is quiet. It breaks up, as I crank the volume, like it used to. It just puts out what sounds like about a 1/4 of a watt of power.
Schematic and voltage checks are next. think I need a break for a bit.
Any tips on getting to the bottom of this are appreciated.
Thanks. Keith
When I fire up the amp now, the amp makes noise with a guitar but it's quiet. It almost sounds like the OT signal is grounded or something. I have been racking my brain for hours over this symptom. Trying different things to no avail. I have got myself worked stupid over it and need to take a break and a fresh new look after a rest.
I've tried swapping in known good tubes.
Lifted board several times to look underneath and inspect & check wiring
Checked and rechecked all wiring many, many times.
I replaced 2 coupling caps and the 2 cathode caps.
Checked all my contacts for grounds or not as required.
I have tried different speakers and cords and guitars to eliminate those variables
Chopstick entire circuit when on, it's all nice and quiet
I have switchable NFB. I hear a little crackle when I switch it on and off. Same as before. I also removed NFB completely to eliminate that option. No improvement.
I lifted board and tested amp. To make sure nothing under the board was touching ground. No improvement.
Tone and volume knobs work as they should.
Just the amp is quiet. It breaks up, as I crank the volume, like it used to. It just puts out what sounds like about a 1/4 of a watt of power.
Schematic and voltage checks are next. think I need a break for a bit.
Any tips on getting to the bottom of this are appreciated.
Thanks. Keith
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