• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

On Line Tube Learning for newbies....

Your amp is a 2 channel guitaramp with a transistor poweramp.The 2nd. channel has one double tube in the signal path only. It is very unlikely that the tube is faulty. Do you have equipment to start a test procedure? You will need a multimeter, a sinewave generator and an oscilloscope to do a proper repair job.A power load (4 or 8 Ohm resistor that can handle your amplifier output in Watts) would be very handy too.
But have a quick look at the bottom of the board, in many cases there are solder and contact problems, such as items not soldered properly or worn out jack sockets who act as "switch" too etc.
 
I can host anything you want to put up

I did notice that your post was, well quit old but so am I so.
If you want to put any techy thing up for everyone let me know.
Servers are quit good everywhere I have ever surfed to them from.
I love most anyting with wires in it.
I come from a telecom, radio, TV, repair family 3rd generation, so me an childhood friend coined it long ago, when we used to tear old radios and amps apart and try to make them work or better. "If it's got wires, it's our's.
 
still wondering where to start

The links in this thread that still work are AWESOME !! (A bunch of the early post links are no longer valid) They help greatly in an understanding of the tube operation and related items, but they still don't say anything about where to start either in acquiring [what type or brand] of amp to start with, which ones are better than others, what to AVOID, ect.
If we are interested in learning to fix, what equipment will we need, (what equipment to AVOID) and any of the so called "kits" available -- are they good to build your own?
I know there will be a wide range of opinions, however, it would be good to get all that input from everyone "in the know" for us who are looking to buy our first tube amp (pre amp???) what speakers, what turntable, what reel to reel, ect.
 
NEETS do that

8th Grade taught Physics!?

What about a guide for people getting into tube audio whom never got Physics in high school?

I rather like this glossary...Tube-Cad Glossary

Edit: Btw that pdf file is really an excellent resource thanks !
The NEETS modules do exactly that. They start with matter, energy, free electrons, electron cloud, that sort of thing. As the man said, VERY thorough.
If nobody mentioned it, the Forrest Mims series of books are great for beginners in electronics. solid state amplification isn't all that different from tubes and he really makes it dirt simple.
Also, Max Robinson has Fun with Electronics, Fun with Tubes, etc. EXCELLENT place for beginners and nonbeginners alike.
 
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Any recommendations for reading about transformer design, winding, core consideration, etc?

There is a boatload of stuff if you look up 'transformer design' or 'transformer design how to'. The issue is really what is the language you're looking for and how much of it. Mostly numbers?, mostly words?, and how detailed . . . . . .

Here's a good page and here's another

HTH
 
I have made an attemt to explain how tubes are working...did I have any succes?

Rectifier tube

Simplest tube with to electrodes
Around the cathode which is glowing is found a cloud of electrons and vhen plate becomes positive the electrons pulls towards the plate ... which means passing current in the tube. If we use the tube as rectifier ... (All tubes can be used as rectifier), we expose the plate to AC power ... it is exposed to both negative and positive voltage pulses a '60hz...only the positive are passed...hopefully. ... It makes a ripple frequency of 60 Hz as single and 120Hz as full wave rectifier.

Triodes

In a triode, we have cathode, grid and plate ... we know nothing happens until the cathode is red-glowing and there is a positive voltage on the plate. Glowing metal emits electrons which are negatively charged regardless of how it is glowing ... so they don't come from the filament voltage.
In triodes current can be controlled using a negative voltage on the grid ... why negative. It must be linked to what I said before that of the cathode emitted electrons are negatively charged and 2 negative things repel each other as well as 2 positive (natural law). The plate is positive and attracts negative electrons ...
+ Attracts - ... that makes sense and between the cathode and plate are grid which repels with its negative charge. The electrons can not get through the grid which repels them and the flow is restricted or completely stopped if negative voltage is high enough .... it's the one limit ... the second limit is 0V on the grid resulting in full current flow in the tube.

All the emitted electrons will flow to the plate. Increasing slowly plate voltage from 0 to 150 V will see the current increase with the plate voltage and come to a point where the current no longer increase in the tube. This point is called the saturation point ... ... ... the tube is saturated...all the electrons are used.

Working as a triode amplifier it must have an idle current as may be below or close to half of the current in saturation point. It is determined by the negative voltage on the grid and over the tube's plate resistance is now a voltage drop least 50V ... and now the tube behave as a amplifier because small voltage changes on the grid causes large current changes in the plate. So the corresponding voltage changes over the anode resistance is the amplified signal ... and here ve use a capacitor which blocks the plate supply (The coupling capacitor) and return a clean amplified signal.

Tetrodes

G2 screen grid is what separates tetrode from triode

It was often a certain logic when we gave the names in the old dayes and screen grid is no exception to this is exactly what it is. Triodes have bad efficience because of the plate static influence of the controle grid and this is where screen grid enters. It is often supplied with voltage equal or less than the plate.

Because of the screen grid the control grid is no longer exposed to the electrostatic influence of the plate ... and what happens then. Now we have a tetrode with completely new properties ... the low internal resistance has gone high and the gain equally. In amplifiers, we have virtually no use for these properties, but there has been an important thing and it's efficience.

When we use triodes in the output we get only half the power tetrode can provide because they can not exploit the supply voltage, but it has a price to use tetrodes ... they distort a lot more. In practice this is not a problem by dimensioning correct and not at least use ultralinear coupling.

Screen grid can also be used as a control grid and connected to special outlets on the output transformer. These outlets are located 20-40% measured from the midpoint of OPT ... it can be called local feedback and the resulting output impedance reaches near triodes...

The result is that tetrode now come to work partly as a triode, but retains virtually efficiency and I am very happy to use this solution.

Pentodes/Beam tubes

The fifth electrode (G3) was invented by Philips around 1928 and called a suppressor-grid and as the name suggests , it captures something. When you want to catch something it's often something unwanted and this is secondary emission. With the introduction of screen grid (G2) got greater efficiency ie. bigger swing at the plate, but also a problem.

As the plate swings against very low value as 50V or less you can with good will say that the flow starts to run the wrong way in the tube. The plate starts emitting electrons absorbed by the screen-grid and it can become overheated and the tube starts to distort heavily. It gives a little twist (kink) on the amplification curve.

Therefore, trap-grid invented ... its located between the screen grid and plate ... the potential is almost always 0V as it usually is connected to the cathode. Here it can catch and throw the unwanted secondary emission from the plate back to the plate and the tube can work much better.

The Americans could not make pentode tubes because they were patented by Philips, but invented the beam power tetrode ... it summarized the electron flow in the tube in a certain way so that the unwanted secondary emission does not occur. Thus they avoided trouble with Philips and got the benefits of the´pentodes ...
 
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Tube mania said:
I have made an attemt to explain how tubes are working...did I have any succes?
Somewhat limited success. Try again when you have gained a better understanding. A tutorial article should be clear and correct, both technically and in language terms. Best to get it checked by a native speaker if possible.

jlangholzj said:
Has some good explanations and so forth on it.
I found it a bit confusing. Too much detail, some of it wrong. For example, very few circuits would design a grid stopper to have a 20kHz rolloff. He determines extrapolated valve characteristics at 0V Vg-k bias, but doesn't actually run the valve at that bias so his gain calculation is a matter of fiction. His wrong results (shown to be such by the simulation) are then said to be "fairly accurate". My guess is that he has understood something, but not as much as he thinks he does. I hope he doesn't teach electronics!
 
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I think the best advice is make sure you start with something likely to work. I would keep away from negative feedback and push pull. The RH 34 amp is an OK place to start.

If I was starting again I might buy this.

6J8P(or 6N8P)+FU-50 SE Tube Amplifier Kit SRK-06 - Boards | Kits | Components | Modules | Tools

The kit has feedback. Should work very well without it. It is the resistor saying 3.5 to 7.5 K next to FU 50. FU/GU/LS 50 is a nice valve in the EL 34 mold with more power.
 
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I am one of the most stupid people I know of. Often I have to relearn to do something. In relearning I really learn. Sometimes I was sick and did not go to the vital class in electronics when lets say 18. I managed because I learnt recipes of electronics. I often learn little things that maybe every other engineer already knows, but I don't.

I never really learnt load lines. I understand them well enough. I do it another way. I make sure the valve is safe. I then use a spectrum analyser to find my best compromise. I often seem to find examples that are nowhere in the text books. This can be very valuable when doing cancellation of distortion. I sent a design to some experianced designers. I was told it would be impossible to repeat the design. This was untrue as I have a bucket of valves to test. I had factored it in. They had learnt too much and didn't think it possible. Some of the valves were 70% emmision. As I was using 20% they were possible. It was a nice use of devices that were thrown away. The results varied between 1% and 1.5 % THD with the same curves. I can live with that. It did talke me 6 months to try many ideas. I just did an hour each day. I had no disasters. I set the pentode by guessing. I never bettered it. Whatever angel was helping knew pentodes.

Never be too proud to be a Newby.
 
.... I propose these for starters, as being sufficiently and as covering enough ground to allow one who understand basic electronics (8th grade physics really) to understand "TOOBZ"!....

Thanks for those two links. Really helpful.

But - uh - where did YOU go for eighth grade? Our high school had twelfth grade physics, and it didn't touch on electronics beyond how to use a dry cell battery and some wire to make a light bulb glow.

I've searched my whole state (Maine) to find some sort of class in electronics basics. Adult ed. The electricians union's training center. Community colleges.

I did find one community college sixty miles away that offers a two-semester intro to electronics, but there's a two-semester algebra/trig prerequisite. So, in all, it would cost me over $900 (plus travel expenses) and take almost two years to get through the course - all to build a guitar amp of equal value.

That would be fine if I were planning on going into the amp-building business, but at 63, I'm not interested in going into ANY business. I just got out of one!

Fortunately, there are plenty of folks online (like you!) who offer plenty of good information. I'm working on my first build now, turning a Hammond organ amp into a guitar amp, and it's all possible because of patient techs who seem to enjoy passing some of their extensive knowledge along.

In this throw-away world of ours, that's good news. The more people who can make and fix things, the less we'll need to depend on big-box store shelves packed with designed-to-break-and-replace goods.

So - glad you're here. Keep up the good work - and the good advice.