DIY Valve Guitar Amp Head

[Guvna19]

Cheers Marcel / Doc, no idea what the said 'glaring failure is'

My Dad was an electrician and i have 2 older brothers in W.A. one being an ex Navy electronics technician and the other a highly qualified sparky. unfortunately I dont get to utilize their skills as they both work heavy shifts in the mining industry and have little spare time.
They all used to chat electronics and engage in dozens of Dick smith projects at the dinner table, which at the time bored me to tears so I chose an alternate career beginning as an apprentice painter. Now aged 45 and still in the paint industry, i have a growing interest in the guitar-amp related electronics area and wish i paid more attention at the dinner table.
I will look into some jaycar projects as you suggest. Know of any projects that serve as usefull tools for future projects , (i dunno, like a voltage meter or somthing?)

cheers
Guv

[Marcel]

I've seen at my local Jaycar store some stomp box kits. Fuzz box type things. Never tried one as I have a TS9 and two other distortion pedals so never felt the need myself to build a fuzz kit. Some of the loud speaker audio amp kits look interesting. It is more a decision of what you have a need for at the time and is building a kit the less expensive way to go...

One kit I did build recently was a DC motor speed controller, with the aim of building a pickup wining machine. Runs on 12VDC so a small sealed lead acid (SLA) battery and a 12V plugpack would see you all powered up. Could even run it on a few D cells if you wanted. I'm still working out how to add a counter so I get the right number of turns on any pickups I may wind.

As for multimeter kits I think buying a complete digital meter is a cheaper and more reliable choice when first starting out as you need to be able to trust the meter you are using. But if you can find a cheap analogue meter then grab it as they are great for testing pickup polarities.

[Marcel]

That's the same approach I took to learning Electronics, I started off with the simple circuits and when I felt that I understood how they worked, I progressed onto more complex circuits, same with actually building them.

That is so right Doc. And I did the same...

Start with simple things with only a few components. learn a few of the laws like ohms law and the power law, then add things like how to calculate impedance of a cap or a coil, and so on... they are all steps that all who are interested must learn and follow,... step by step,, and all the while applying what you learnt to your build...

Not that much different in principal to building a guitar really....lol

[DrNomis_44]

That is so right Doc. And I did the same...

Start with simple things with only a few components. learn a few of the laws like ohms law and the power law, then add things like how to calculate impedance of a cap or a coil, and so on... they are all steps that all who are interested must learn and follow,... step by step,, and all the while applying what you learnt to your build...

Not that much different in principal to building a guitar really....lol

It was only when I started doing formal studies in Electronics that I was finally able to understand Impedance and how it varies with frequency in Inductors and Capacitance, I also learnt that you can cancel-out the effects of Inductive-Reactance and Capacitive-Reactance if you make both the Inductor and the Capacitor equal in value, at some frequency the two equal and opposite-phase Reactances will cancel each other out, and you will be left with pure DC resistance, which is usually a very low value, this is basically how a passive series LC bandpass filter works, my Fender Super Twin uses them in it's EQ circuit, each frequency band is determined by the relative values of the Inductor (L) and Capacitor (C), pretty interesting how they did things back then, nowadays circuit designers use a special Op Amp circuit to replace/simulate an Inductor, it's a circuit called a Gyrator, basically it inverts the behaviour of a capacitor so that it looks like the behaviour of an Inductor.

Hopefully I'm remembering my electronics theory correctly.

[Marcel]

Yeah Doc, can't fault what you wrote so your theory is up there...

Personally, I still can't get over the fact that some people (particularly on other forums) truly think that an active circuit using an Op-amp and a capacitor imitating and inductor is better than a real (passive) inductor made from simple copper wire.... True, the Op-amp circuit maybe more versatile, but still it amazes me...

But I do appreciate some of the wicked and awesome things than can be done with electronics (in all its forms) these days. I've worked on all sorts of gear, some that operate from DC all the way through to gear that works on damn near daylight yet there near isn't a day goes by where I don't encounter some new way of doing things with electronics... so it is refreshing to 'dive into' a good tube job where the technology hasn't really changed much in decades.

One thing that does get 'up my goat' and yet I often have a good laugh over is the fault finding techniques that are there for all to see on YouTube... There are few that achieve in my opinion a 'Good' status, and one or two who are expert, but where I get the best laughs are those who fumble about and change parts willy-nilly for an hour or two until the poor amp gives in and starts to work again...

[DrNomis_44]

Yeah Doc, can't fault what you wrote so your theory is up there...

Personally, I still can't get over the fact that some people (particularly on other forums) truly think that an active circuit using an Op-amp and a capacitor imitating and inductor is better than a real (passive) inductor made from simple copper wire.... True, the Op-amp circuit maybe more versatile, but still it amazes me...

But I do appreciate some of the wicked and awesome things than can be done with electronics (in all its forms) these days. I've worked on all sorts of gear, some that operate from DC all the way through to gear that works on damn near daylight yet there near isn't a day goes by where I don't encounter some new way of doing things with electronics... so it is refreshing to 'dive into' a good tube job where the technology hasn't really changed much in decades.

One thing that does get 'up my goat' and yet I often have a good laugh over is the fault finding techniques that are there for all to see on YouTube... There are few that achieve in my opinion a 'Good' status, and one or two who are expert, but where I get the best laughs are those who fumble about and change parts willy-nilly for an hour or two until the poor amp gives in and starts to work again...

Yep, some people forget to realize that Op Amps, being active devices, do introduce noise and distortion into a circuit, that's the nature of active devices, valves introduce noise and distortion into a circuit too but they produce different distortion harmonics due to the non-linearity inherent in valves, the noise is produced by the electrons boiling off the cathode during thermionic emission.

When I'm fault-finding a piece of electronic equipment I always try to maintain a logical approach to it, and treat it as if I'm a detective working on solving a mystery.

[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.

[Marcel]

My worst experiences with noise were during World Expo 88 in Brisbane.

The first was with the new you-beaut latest model 32 band stereo graphic equalisers that were in use everywhere and used a proprietary chip that often went noisy. I must have replaced at least 100 of those 12 pin inline goop encased sub-boards that held the chip which for nil obvious reason would randomly simply start generating higher levels of hiss that was not unlike a reverse biased diode.

The second was the Soundcraft 40ch/16bus foldback console on the river stage. The sound guys and the artists all complained about the poor noise floor while doing shows, so we contacted Soundcraft in the UK. They were very nice yet somewhat apprehensive when they advised of a modification that could be done to this $150k console. Ultimately after many phone calls and various assurances I performed the modification which involved a number of wire and solder changes and taking a dremmel to every board in the desk... I had a 11hr window to do the work which took 9hrs with the dremmel and all the while in the back of my head I knew that this one desk was worth more at the time than most inner city Brisbane CBD apartments, plus the desk had to be back in service by 10am.... The mod worked fine but it was Yay, and team me totally stressed out and dead dog tired by the end...

A side note of trivia - my avatar is a pic of some Gold Silk embroidery on a Black denim jacket I had done at the China pavilion during the Expo...

[DrNomis_44]

My worst experiences with noise were during World Expo 88 in Brisbane.

The first was with the new you-beaut latest model 32 band stereo graphic equalisers that were in use everywhere and used a proprietary chip that often went noisy. I must have replaced at least 100 of those 12 pin inline goop encased sub-boards that held the chip which for nil obvious reason would randomly simply start generating higher levels of hiss that was not unlike a reverse biased diode.

The second was the Soundcraft 40ch/16bus foldback console on the river stage. The sound guys and the artists all complained about the poor noise floor while doing shows, so we contacted Soundcraft in the UK. They were very nice yet somewhat apprehensive when they advised of a modification that could be done to this $150k console. Ultimately after many phone calls and various assurances I performed the modification which involved a number of wire and solder changes and taking a dremmel to every board in the desk... I had a 11hr window to do the work which took 9hrs with the dremmel and all the while in the back of my head I knew that this one desk was worth more at the time than most inner city Brisbane CBD apartments, plus the desk had to be back in service by 10am.... The mod worked fine but it was Yay, and team me totally stressed out and dead dog tired by the end...

A side note of trivia - my avatar is a pic of some Gold Silk embroidery on a Black denim jacket I had done at the China pavilion during the Expo...

Now that you mentioned Soundcraft gear, a good mate of mine got me to do some restoration work on his 80's vintage 28 Channel Soundcraft mixing desk, apparently some rats or other rodents got into it and randomly chewed the ribbon cabling to pieces, I had the job of cutting out all the worst-chewed pieces and splicing all the good bits together, I had to literally solder and heatshrink 80+ individual strands of wire every time I spliced the ribbon cabling together, incidentally the ribbon cabling was what distributed the audio signals from each of the 28 Channels, so it was a big job, I eventually got it to the point where it was something like 80% working and had to turn my attention to a mini-jack patch panel, I was getting signal to pretty much every part of the patch panel as it was supposed to, but there was one mini-jack that appeared to be faulty, I decided to use a X10 magnifying loupe to give the suspect jack a good eyeball and as it turned out the cause of the fault turned out to be an insignificant piece of lint wedged between two contacts, I cleaned it out and the mini-jack worked normally again, the guy who owns the Soundcraft desk runs a recording studio and wants me to do a re-cap job on all the channel strips to get each one sounding consistent so he can use it as part of his studio setup, most of the caps in the channels are electrolytics which I'm guessing are easily over 20 years old by now and are probably due for replacement, they are all RT style that are wrapped in a translucent-blue film, looks like a fun job for me, I still have fond memories of the work I did on it, tracing out all the signal paths with my Signal-Generator and Oscilloscope.