I have acquired some time ago an Engl Savage 120 (built in 2011) which I guess never sounded "right", just kinda average. I have retubbed it, re-biased, tried all kinds of tubes in, but it never sounded as brutal as I would like it to be. And I am mostly talking about the high gain distortion on channels 3 and 4 (CrunchII and Lead). It always felt as missing something to sound full/right. The Clean and CrunchI channels sound alright, but I rarely use them. I also own an Engl Fireball 60 which is just great.
Now I have come to think that there might be something wrong with the actual distortion or something else is faulty. I have a general understanding of electronics and tube amps and I am able to repair faulty components, but it is a pain to remove the main PCB to check all the components one at a time. I could also add that the PCB is of very poor quality, thin traces and the like, easy to destroy. Therefore I am hoping someone might be able to chime in on this.
Engl Savage E610 Schematic: engl-savage-120-type-e610-schematic.pdf
I have done some tests with the oscilloscope, applying a 1KHz, 150 mV input signal to see what kind of output do I get across the speaker output. I have tested channels 2 and 3 (Crunch I and Crunch II) on roughly everything set to noon and this is where I can see some interesting results.
- On CrunchI I get a good distorted sound which has the fundamental frequency as well as 3rd harmonic quite high and so on. I assume this is good, as the signal looks symmetrical.
Output waveform as well as frequency components in purple (1KHz, 3KHz peaks):
- On CrunchII I get a distorted sound which has the 2nd harmonic very high and as far as my knowledge goes, it appears the preamp tube is cold biased somehow (not properly biased by the cathode resistor + capacitor) as it is kinda clipping/distorting on the low level input.
Output waveform as well as frequency components in purple (1KHz, 2KHz peaks):
Looking over the schematic, I can see that V2b preamp tube is responsible for Crunch II and there is a switch S11b which adds the capacitor in parallel to the cathode resistor. I do not know where that switch is located and maybe there is something about it that changes the waveform or there is something faulty in there. Following the schematic I can see that switching to lead channel adds the V3b gain stage. I have tested the output on the lead channel and it is actually symmetrical with just fundamental + third harmonic, not much content in the second harmonic. If there is something faulty at the V2b stage, I assume is roughly affecting the subsequent gain stage as well, which might explain the sound lacking full body, but could it be that V3b might correct any misbalance further on? I am a little puzzled.
Basically I have a few questions. Is anyone able to judge if this asymmetrical waveform is the way it is supposed to look on Crunch II compared to the symmetrical Crunch I?
If this is not how it is supposed to look like, should I then look at replacing the V2b cathode resistor and bypass capacitor/switch? Or could there be other issues to look for?
Also, maybe it is worth mentioning, but when the amp is turned on with Master Volume set to MIN, I get a 400 kHz sine output (range over a few Volts) that goes away when I turn up the volume. Is this normal?
Appreciate any suggestions/advices.
Now I have come to think that there might be something wrong with the actual distortion or something else is faulty. I have a general understanding of electronics and tube amps and I am able to repair faulty components, but it is a pain to remove the main PCB to check all the components one at a time. I could also add that the PCB is of very poor quality, thin traces and the like, easy to destroy. Therefore I am hoping someone might be able to chime in on this.
Engl Savage E610 Schematic: engl-savage-120-type-e610-schematic.pdf
I have done some tests with the oscilloscope, applying a 1KHz, 150 mV input signal to see what kind of output do I get across the speaker output. I have tested channels 2 and 3 (Crunch I and Crunch II) on roughly everything set to noon and this is where I can see some interesting results.
- On CrunchI I get a good distorted sound which has the fundamental frequency as well as 3rd harmonic quite high and so on. I assume this is good, as the signal looks symmetrical.
Output waveform as well as frequency components in purple (1KHz, 3KHz peaks):
- On CrunchII I get a distorted sound which has the 2nd harmonic very high and as far as my knowledge goes, it appears the preamp tube is cold biased somehow (not properly biased by the cathode resistor + capacitor) as it is kinda clipping/distorting on the low level input.
Output waveform as well as frequency components in purple (1KHz, 2KHz peaks):
Looking over the schematic, I can see that V2b preamp tube is responsible for Crunch II and there is a switch S11b which adds the capacitor in parallel to the cathode resistor. I do not know where that switch is located and maybe there is something about it that changes the waveform or there is something faulty in there. Following the schematic I can see that switching to lead channel adds the V3b gain stage. I have tested the output on the lead channel and it is actually symmetrical with just fundamental + third harmonic, not much content in the second harmonic. If there is something faulty at the V2b stage, I assume is roughly affecting the subsequent gain stage as well, which might explain the sound lacking full body, but could it be that V3b might correct any misbalance further on? I am a little puzzled.
Basically I have a few questions. Is anyone able to judge if this asymmetrical waveform is the way it is supposed to look on Crunch II compared to the symmetrical Crunch I?
If this is not how it is supposed to look like, should I then look at replacing the V2b cathode resistor and bypass capacitor/switch? Or could there be other issues to look for?
Also, maybe it is worth mentioning, but when the amp is turned on with Master Volume set to MIN, I get a 400 kHz sine output (range over a few Volts) that goes away when I turn up the volume. Is this normal?
Appreciate any suggestions/advices.
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