Amp techs and tinkerers: where do I get started?

[chee16]

I started by tinkering on my tsl602. Terrible idea, haha. There's probably still a bunch of my old posts asking dumb questions and thinking I figured things out when I didn't.

So then I started getting into individual things. Like I read up on how to bias a class AB amp, but then went further and tried to find out what you are doing when you bias the amp. Then I looked into what an output transformer does since that's involved in the bias process, etc.

I'm still far from an expert, but I repair a lot of amps for my local shop.

I'm sure lots will argue with me, but for me I don't bother repairing surface mount boards. I'm not saying anything with surface is bad, just that most of the time for me is more cost effective to replace the board or junk it. Again, please don't take that as no one should, it's just not something I'm capable of or find the need to get into.

I do really enjoy uncle Dougs channel too.
Aikens amplification tech info is great too.

 

[AlvisX]

I got started on these
My unit was responsible for maintaining 20 of these 10kw Tube radio transmitters. i worked there from 1990 to 93 when I was discharged
Made a Marshall look like an easy bake oven ....

 

[GuitarIV]

Your red plating could be tube failing, bias issues, or screen resistor for starters.

The tubes in the 800 are still the original Yugoslavian EIs... the amp is from 82. My tech said after such a long time it's ok for them to go out

I'll order some military grade Tung Sol EL34Bs, I replaced my old tubes in my DSL 100 with these and have no complaints. If we still get red plating, the amp will have to be examined from the inside.

How did you start?

The label said: "no user serviceable parts inside."

I just ignored that, and did it anyway.

Recklessly opening up tube equipment and shocking myself.
Eventually I learned not to shock myself.

Oh yeah, getting shocked is part of the experience.
If you are the type who whines and cries over a few hundred volts, you shouldn't be working on tube amps.

I'm not afraid of a shock, as long as it doesn't run through my heart. My amp tech told me in 40 years of working on tube amps... he got shocked once. So I guess he's the guy to learn safety from

Second vote to build a tweed Champ. If you haven’t been yet, check out all the kits at Mojotone.com. They use good quality parts.

I found a few kits on TubeTown, it's a German company. Since I'm in Austria, Europe, that would be a better option for me:

https://www.tube-town.net/cms/?DIY/LoW-Projekte/Jim

It's basically a Marshall Class 5 kit. If I start somewhere, this looks quite tempting.



Thank you sooo much for all the insights. I will start reading up stuff now and watch Uncle Dougs videos. I am the kind of person that likes to understand why things work the way they do before I tackle em.

I'll refer to this thread whenever I need it, in the meantime keep them suggestions and tips coming, I see I'm not the only one who has taken an interest!


Cheers guys and stay healthy

 

[NewReligion]

The tubes in the 800 are still the original Yugoslavian EIs... the amp is from 82. My tech said after such a long time it's ok for them to go out

I'll order some military grade Tung Sol EL34Bs, I replaced my old tubes in my DSL 100 with these and have no complaints. If we still get red plating, the amp will have to be examined from the inside.



I'm not afraid of a shock, as long as it doesn't run through my heart. My amp tech told me in 40 years of working on tube amps... he got shocked once. So I guess he's the guy to learn safety from



I found a few kits on TubeTown, it's a German company. Since I'm in Austria, Europe, that would be a better option for me:

https://www.tube-town.net/cms/?DIY/LoW-Projekte/Jim

It's basically a Marshall Class 5 kit. If I start somewhere, this looks quite tempting.



Thank you sooo much for all the insights. I will start reading up stuff now and watch Uncle Dougs videos. I am the kind of person that likes to understand why things work the way they do before I tackle em.

I'll refer to this thread whenever I need it, in the meantime keep them suggestions and tips coming, I see I'm not the only one who has taken an interest!


Cheers guys and stay healthy

I assumed you did basic trouble shooting to identify if it is related to that socket or that tube. Just put that tube in a different socket to see if the issue follows. If not it is not the tube.

David

 

[GuitarIV]

I assumed you did basic trouble shooting to identify if it is related to that socket or that tube. Just put that tube in a different socket to see if the issue follows. If not it is not the tube.

David

Good idea, will do! I'll keep you guys posted.

I love that amp. It's a beast:

 

[South Park]

You need to go to school for this stuff start with the basics . Junior collage night school is a good start . And read every thing you can about tubes . Some of us make it look easy. This stuff will put you on the short bus real fast

 

[Matthews Guitars]

I'm going to reiterate my belief that you'll be miles and years ahead (months at least) to learn electronics as a formal education FIRST.

It actually doesn't take very long to learn it. There isn't any reason NOT to. I'd say that if you're a quick learner you should be able
to learn DC electronics in a matter of just a couple of weeks with a couple hours of study per evening.

AC electronics won't take much longer.

You've heard about biasing tubes. You probably know that bias problems can lead to red plating tubes. But do you know WHY?
When you adjust the bias, do you have an image in your head of how the conduction cycle on each power tube is changing?

If you swap out a plate resistor to change the gain level of a tube stage, do you know WHY it's changing the gain?

If you change the value of the resistor leading from cathode to ground, do you know what you are doing to the operating point of the tube, and why?

If you change the value of the bypass resistor jumping across the cathode resistor, do you know what the effect is, and why? Do you know what will
happen if you completely remove that capacitor? Or, if there isn't one, if you add one?

Can you explain the difference between conventional gain stages and a cathode follower? And why it's different?

How about the differences between single ended and push-pull output stages?

If you don't have these answers, you don't really know how the amp works. If you don't really know how it works, you can't modify it in ways that you
can predict. You can copy the work of others. You can follow directions. That makes you an ASSEMBLER, and that is a useful skill.

But if you are just swapping parts out to see what happens, that's an empirical design process which is less efficient than engineered design.

Engineering is knowing how things work and how to put them together with the ability to predict their interactions in order to achieve a goal.

If I have a 12 volt power supply that can deliver 10 amps of current at 12 volts, and I tell you to pick a resistor to place across the power supply terminals,
that will draw five amps of current, how many watts of power will that resistor have to dissipate, and what will be the value of that resistor?

If you can't answer that question, you're shooting in the dark.

 

[ampmadscientist]

I got started on these
My unit was responsible for maintaining 20 of these 10kw Tube radio transmitters. i worked there from 1990 to 93 when I was discharged
Made a Marshall look like an easy bake oven ....

Oh yeah what do ya know? I worked on Collins and Harris transmitters.

 

[SmokeyDopey]

Another recommended channel is MrCarlson's Lab. He is more technical than Uncle Doug, but he is very clear and you can tell he has a lot of experience. He sounds like a professor.

 

[MickeyJ]

You need to go to school for this stuff start with the basics . Junior collage night school is a good start . And read every thing you can about tubes . Some of us make it look easy. This stuff will put you on the short bus real fast

My school was the local rubbish dump and any poor appliance that was on the way out. Into my grubby kid hands the appliance would go and it would be in pieces in minutes.
Nothing was safe, lawnmowers, televisions..motorbikes, cars.
Today, I fix washing machines, amps, cars..anything that can be pulled apart and viewed internally.
I learnt how to read a schematic way after I learnt how to fix amps, There's nothing to them..and remember, most amps are the same, like, really the same. Schematics are handy to me, but just that, no more.
I'd prefer a screwdriver and a soldering iron any day.

 

[MickeyJ]

fixing amps is one thing

- tuning them is another entire thing.
no matter what you do, or don't do..keep listening to everything.
your ears are your most valuable and effective tool...perhaps after a multi-meter.

 

[NewReligion]

These are all great points.

I will add some of the best builders had little if no formal education. It is important but often engineers can build a stable working circuit but without the ears of someone like say Mark Cameron the amp often sounds sterile and lifeless.

It is easy enough to build a clean circuit but in building high gain everything becomes critical sonically. Open foil orientation for example with capacitor values of .002uf and less.

Now you have heard the best from many offerings that I think to be great advice.

Decide what works for you, your station in life & where you wish to land. No one can know it all.

Be safe, learn what you can, use your ears as many guys just are not gifted and this can not be learned.

With all of this data you may feel overwhelmed. Take notes, bookmark and choose subjects to study as fortes which apply to your interest.

Best to all, David

 

[giam23]

I'm going to reiterate my belief that you'll be miles and years ahead (months at least) to learn electronics as a formal education FIRST.

It actually doesn't take very long to learn it. There isn't any reason NOT to. I'd say that if you're a quick learner you should be able
to learn DC electronics in a matter of just a couple of weeks with a couple hours of study per evening.

AC electronics won't take much longer.

You've heard about biasing tubes. You probably know that bias problems can lead to red plating tubes. But do you know WHY?
When you adjust the bias, do you have an image in your head of how the conduction cycle on each power tube is changing?

If you swap out a plate resistor to change the gain level of a tube stage, do you know WHY it's changing the gain?

If you change the value of the resistor leading from cathode to ground, do you know what you are doing to the operating point of the tube, and why?

If you change the value of the bypass resistor jumping across the cathode resistor, do you know what the effect is, and why? Do you know what will
happen if you completely remove that capacitor? Or, if there isn't one, if you add one?

Can you explain the difference between conventional gain stages and a cathode follower? And why it's different?

How about the differences between single ended and push-pull output stages?

If you don't have these answers, you don't really know how the amp works. If you don't really know how it works, you can't modify it in ways that you
can predict. You can copy the work of others. You can follow directions. That makes you an ASSEMBLER, and that is a useful skill.

But if you are just swapping parts out to see what happens, that's an empirical design process which is less efficient than engineered design.

Engineering is knowing how things work and how to put them together with the ability to predict their interactions in order to achieve a goal.

If I have a 12 volt power supply that can deliver 10 amps of current at 12 volts, and I tell you to pick a resistor to place across the power supply terminals,
that will draw five amps of current, how many watts of power will that resistor have to dissipate, and what will be the value of that resistor?

If you can't answer that question, you're shooting in the dark.

Ive watched uncle dougs videos on power supplies and pre amps, specifically on the fender champ, and im fairly confident that I understand most of the schematic, the only thing im unsure of is pretty much anything cathode based, what are the 1.5k resistors to ground on the preamp cathodes, why is the second stage cathode linked to the speaker side of the output transformer?

would be good if anyone could try explain this too me, also seen on alot of high wattage marshalls, a split from the cathode, and a cap and a resistor leading to ground

 

[MickeyJ]

"what are the 1.5k resistors to ground on the preamp cathodes"

those resistors draw voltage from the chassis and bias that half of the ecc83/12ax7.
they are cathode resistors, just like on a cathode biased amp. ( output tubes)
you just read the voltage across that resistor, the cathode voltage.

 

[NewReligion]

fixing amps is one thing

- tuning them is another entire thing.
no matter what you do, or don't do..keep listening to everything.
your ears are your most valuable and effective tool...perhaps after a multi-meter.

This big time as I was working in this direction of a talking point as Mickey posted it as I was typing.

Peace out.

David

 

[Matthews Guitars]

If you take the time to learn the electronics theory and math, you'll have it for life.

Don't think that skipping it is a shortcut. It''s the long way to knowing what does what and why.

 

[MickeyJ]

why is the second stage cathode linked to the speaker side of the output transformer?

i think some of the output signal from that output transformer is sent back through that resistor to the cathode as a negative feedback system.

 

[giam23]

"what are the 1.5k resistors to ground on the preamp cathodes"

those resistors draw voltage from the chassis and bias that half of the ecc83/12ax7.
they are cathode resistors, just like on a cathode biased amp. ( output tubes)
you just read the voltage across that resistor, the cathode voltage.

oh okay, does there need to be a specific voltage for operation or it varies, does it depend on how much voltage is being dumped to ground in that circuit to set that value, is there any problem of not including that resistor?

 

[Matthews Guitars]

The cathode resistor sets the bias point of the tube.

Higher resistor values change the operating point toward cold clipping. (Cutoff)

Lower resistor values change the operating point toward peak saturation.

And then there's the bypass capacitor:

https://www.ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/


Learn electronics theory. You're asking questions that are answered a couple of months into the program and you won't fully understand them without having the background.


You need to back up and start with DC theory and Ohm's Law. Just like everybody else who actually got curious and ended up learning enough to be able to understand how it works and make changes that achieve a defined goal.

https://www.instructables.com/class/Electronics-Class/

https://www.skillshare.com/classes/...wse-rating-electrical-engineering-layout-grid

 

[MickeyJ]

oh okay, does there need to be a specific voltage for operation or it varies, does it depend on how much voltage is being dumped to ground in that circuit to set that value, is there any problem of not including that resistor?

you need to be within a range of voltage, yes, otherwise you will burn the tube.

i think you can ditch the capacitor, not the resistor.


i just watched uncle dougs video.



quite hard to follow.

what he's saying is that because the cathode is drawing electrons from the chassis, so that the cathode can get heated and send its particles upwards through the grid ( in a vacuum, it all flows one way, from the cathode to the anode)...it draws electrons ( voltage ) through a resistor ( your cathode resistor)..Now, because the cathode has drawn those electrons, it is now lets say 25vdc.
And, because the grid, which is tied to ground through a grid leak resistor is at 0v, it is negatively charged in relation to the cathode.So, by default ( for the purposes of biasing a tube)...the grid is now seen to be negatively charged.
You change that cathode resistor....you change the amount that cathode is charged ie from 25vdc to lets say 23vdc...and subsequently, you change the negative voltage on the grid.

What a pile of crap...just change the resistor to make the tube run hot or cold.