DIY Valve Guitar Amp Head

[Marcel]

You often see comments like that on videos called "Repairing my Brand XYZ tube amp" where viewers see the video as a detective hunt...

My giggles come mostly from what those guys do during their 'detective hunt'. Particularly when they go off on a tangent chasing some clue to nowhere as they more often than not they have failed to understand what the circuit is doing or should be doing, or they misinterpret a meter reading, or they fail to take any readings with a meter at all. They just jiggle and swap tubes, tap away all over the chassis, and start swapping other bits until finally after 45 minutes of video they go back to what they discovered 10 minutes in and replace the real culprit. Entertainment with a bit of learning thrown in.

My fault finding usually follows the half split rule. This is where you view the faulty whatever as a complete system with an in and a out, or a start and a finish, and you divide it in half. If what you are getting at that point is okay then you know everything before that point is fine and your fault lies in the other half. You then repeat the process on the 'faulty' half, and keep repeating until you get to a point where you can't split it any more. At this point you need to know what that part is doing and also know from the schematic and your experience what it should be doing, and the research any differences. There is a lot more to it but that is the essential basics I follow.

Did you know that EVERY component adds noise. Active devices like tubes and transistors add the most, but resistors and caps and coils and even wire add their fair share too..... all those electrons randomly bouncing from atom to atom in every component....

On another note, A video you might like to watch.... Mullard tube manufacture film from the early '60's... https://www.youtube.com/watch?v=GDvF89Bh27Y

[DrNomis_44]

You often see comments like that on videos called "Repairing my Brand XYZ tube amp" where viewers see the video as a detective hunt...

My giggles come mostly from what those guys do during their 'detective hunt'. Particularly when they go off on a tangent chasing some clue to nowhere as they more often than not they have failed to understand what the circuit is doing or should be doing, or they misinterpret a meter reading, or they fail to take any readings with a meter at all. They just jiggle and swap tubes, tap away all over the chassis, and start swapping other bits until finally after 45 minutes of video they go back to what they discovered 10 minutes in and replace the real culprit. Entertainment with a bit of learning thrown in.

My fault finding usually follows the half split rule. This is where you view the faulty whatever as a complete system with an in and a out, or a start and a finish, and you divide it in half. If what you are getting at that point is okay then you know everything before that point is fine and your fault lies in the other half. You then repeat the process on the 'faulty' half, and keep repeating until you get to a point where you can't split it any more. At this point you need to know what that part is doing and also know from the schematic and your experience what it should be doing, and the research any differences. There is a lot more to it but that is the essential basics I follow.

Did you know that EVERY component adds noise. Active devices like tubes and transistors add the most, but resistors and caps and coils and even wire add their fair share too..... all those electrons randomly bouncing from atom to atom in every component....

On another note, A video you might like to watch.... Mullard tube manufacture film from the early '60's... https://www.youtube.com/watch?v=GDvF89Bh27Y

I think that a lot of those Youtube service techs probably fail to realize that the actual fault-symptoms can be a very valuable clue to where the fault is most likely to be, I'm currently working on tracing the source of some crackly noise in my Moen Pretty Dolly Delay pedal, so far what I've done is given the pots a spray with some contact cleaner, it didn't fix the crackly noise but it eliminated one cause, I'm starting to suspect that the noise is being generated by a JRC4558 IC, but I may be wrong, I'm going to try substituting a TLO72 IC for it, I know that JRC4558 ICs are inherently noisy, and since the TLO72 is a low noise pin-for-pin compatible IC, it should work fine, other than the noise issue the pedal works fine, it's just a bit too noisy for use on my pedal board, my Boss RE20 Space Echo is much quieter in comparison, but I might just do some tracing with my Oscilloscope first though.

Actually, I didn't know that even wires generate noise, I guess if it has moving electrons in it, anything in the circuit can generate noise regardless if it's active or passive, even reverse-biased silicon diodes will generate noise, that's the classic way of generating noise in Synthesizers, either a reverse-biased diode or Transistor B-E junction.

I'll check out that link you posted, cheers.