Lifting R56/54 made no difference. The trimmer pot seems OK...I've cleaned it and it swings properly between one end to the other.
I've discovered that the noise is actually hum (60hz?) as well as hiss. I've grounded some things in the preamp...
Grounding the Base of TR 2 or 3 stops the noises entirely.
Grounding the Base or Emitter of TR1, or the trimmer pot on either end stops the hum, but not the hiss. The noises are of about the same volume so there is no really improvement. So somewhere between TR1 and 2?
I've discovered that the noise is actually hum (60hz?) as well as hiss. I've grounded some things in the preamp...
Grounding the Base of TR 2 or 3 stops the noises entirely.
Grounding the Base or Emitter of TR1, or the trimmer pot on either end stops the hum, but not the hiss. The noises are of about the same volume so there is no really improvement. So somewhere between TR1 and 2?
Ok we're getting somewhere.
I was able to kill the hum by adding the a 3rd filter (.33uf) to the reed bar pickup as shown in later schematics. As for the hiss, the base of TR 1 and 2 are clean. The scope shows noise at the base of TR3.
Thank you so much for your help thus far, I appreciate it
I was able to kill the hum by adding the a 3rd filter (.33uf) to the reed bar pickup as shown in later schematics. As for the hiss, the base of TR 1 and 2 are clean. The scope shows noise at the base of TR3.
Thank you so much for your help thus far, I appreciate it
I've removed R54 and measured again...TR2 base is clean, TR2 collector is noisy just like the TR3 base as before. When R54 is installed I can hear the hiss modulate slightly due to the vibrato circuit, even though the vibrato pot is full CCW. Removing R54 reduces the hiss by about 10%, if that.
Hi,
Let's do another test since by R54 the hiss dropped 10 % and the hum it is gone. Removed again R54 and R51 these will eliminate completely the vibrato from the circuit. If the hiss goes away then the noises it is coming from the vibrato but if still there then noises it is coming from the +15 volts. The TR2 base it is cleaned and collector it is noisy it is possible that the noises must come from the +15 volts.
Let's do another test since by R54 the hiss dropped 10 % and the hum it is gone. Removed again R54 and R51 these will eliminate completely the vibrato from the circuit. If the hiss goes away then the noises it is coming from the vibrato but if still there then noises it is coming from the +15 volts. The TR2 base it is cleaned and collector it is noisy it is possible that the noises must come from the +15 volts.
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