transferring my tube ciruit understanding to solid state circuits?

[Groover]

I have developed a decent basic understanding of tube amp circuits over the course of the last couple of years, largely thanks to this forum and also to Merlin's book.

I am now starting to dabble in stomp box electronics, and I find myself somewhat at a loss trying to transfer my skills to the solid state arena. I can see the resemblance a simple transistor has to a triode, AFAIK source~anode, gate~grid, drain~cathode.
But that is about as far as I get. With op-amps I am more at a loss.

Is there a book or web articles that you could point me to to help me with this?
Does Merlin have any solid state articles? Thanks

[Loogie]

Electrical Engineering Training Series

[octal]

Op amps are just about the easiest gain stages to work with, especially if you're using a dual rail supply (+ & -). There are two basic ways of configuring them (inverting and non inverting), the gain is set by the ratio of two resistors, and if you use a unity gain stable op amp it's all but impossible to go wrong. If you're experimenting, the TLO 72 op amp is a good cheap op amp which sounds decent. Be sure to put bypass capacitors from your +/- pins to ground near your op amp so it doesn't oscillate.

[Enzo]

It is easy to look at tubes and then transistors and think of them as parallel, but really, that will only make it confusing. Transistors work on entirely different fundamental principals. There are many parallel, and things like Ohm's Law don;t care what sort of circuit they are in. But if you don't understand how transistors work, then you won;t know when to look at the parallels and when they don't apply.

SO just learn transistors for their own sake, not as stand-ins for tubes. Tubes operate on voltage while transistors operate on current. Yes, of course where there is on there is the other, but the thinking is different. Here is how I intuit transistors, not very scientific, but it works for me. I learned digital logic before I really learned transistors, so I often think in terms of pullups and pulldowns. In any case, once you get that there are two "polarities" of transistor - NPN and PNP - and which wants what voltage where, then the basic circuits are the same. My little rule of thimb is that if I pull the base of the transistor towards its collector, it will turn on. I guess that is kinda like pulling the grid of a triode towards its plate will make it conduct more.

So in a typical NPN transistor stage, grounded emitter, as I bring the base more positive (draw more current from the base) it causes the transistor to conduct more from emitter to collector. That means the voltage sitting on the collector will drop - from the increased current through the collector load resistance making a voltage drop. Likewise, if I drag the base the other way - toward the emitter and thus ground - it turns the transistor off. The transistor becomes an open.

There are circuits with both NPN and PNP combined. The polarity of current is opposite in each, but that's OK, just turn one of them "upside down" and it will be fine. The thing is with my thinking aid, the rule about pulling the base towards the collector to turn it on still applies. Doesn;t matter if the collector is twoards hot or towards ground.

Look at the attached simple Kustom preamp circuit. Note, this thing uses +8 at the top, and -8v for the bottom, but it also uses ground. Might help to realize that ground is just something 8v more positive than -8v. We could easily convert this to running off +16 and ground. Look at Q100, 101. Q100 is NPN. As the signal at its base goes more positive, that is towards its collector, so the thing conducts more. That will bring that +7.5v at the collector more negative. But wait. That collector is tied to the base of PNP Q101. And as that point goes more negative, it is pulling the base of Q101 closer to ITS collector, so it now conducts harder. DOn;t worry about the details of the circuit stage now, just looking at the example of using my little rule of thumb.

Then there is lonesome Q102, NPN. As the base drive goes more positive, that pulls the base towards the collector an makes the transistor conduct more. Well, that means the +8v and -1v at the collector qand emitter will be drawn closer together. The +8 will drop and the -1 will rise, well, the -1 will become more positive. Rise might be a confusing word.

[Wilder Amplification]

With FETs and MOSFETs -

Source = Cathode
Gate = Grid
Drain = Plate

Just remember that in a tube triode stage the cathode is the "source" of electrons so the "source" of an FET/MOSFET is the equivalent of the cathode. The plate is the "drain" that "drains" electrons back to the positive side of the supply, and the grid is the "gate" that 'opens and closes' to varying degrees to allow more/less electrons flow through to the plate just like varying a FET/MOSFETs gate voltage opens and closes the gate to allow more/less electrons to flow through the source/drain channel.

FETs and MOSFETs are more closely related to tubes than bipolar transistors but Enzo's analogy regarding bipolar transistors is a good one.

With N-Channel FETs and MOSFETs, you can set them up just like a tube stage in that you have a gate leak resistor to ground (just like a triode stage), a resistor that allows the source to be more positive than the gate (or you can use a diode) just like a triode stage, then you have your drain load resistor just like you have a plate load resistor on a triode stage.

[Enzo]

That is true, FETs are very tubish, but the bipolars are in their own world.

[Robert M. Martinelli]

What our friends said.

Better to start afresh with studying BJTs and their basic principles of operation.

The main difference between tubes (valves on this side of the big pond) and BJTs is that the first are VOLTAGE controlled devices: a change in the grid VOLTAGE causes a change in the plate CURRENT; the relationship between them is called mutual conductance, (or transconductance), expressed in mA/V (that is, the change in the plate current you get for a 1V change in the grid voltage).

BJTs are CURRENT controlled devices: a change in the base CURRENT causes a change in the collector CURRENT; the relationship between these two currents is the BJT Hfe (sometimes called Beta, even though they're not the same thing), which is a non-dimensional number (without measuring units) because it's a simple current ratio.

FETs and MOSFETs do indeed work in a tube-like manner, they're VOLTAGE controlled devices too, and so the way they operate sounds more familiar to persons keen on tubes (even though it must be said that their behavior in overdrive conditions is quite different, so they can sound "tubish" only up to a certain point).

JM2CW

Hope this helps

Best regards

Bob

[wizard333]

Any other info besides that EETS which would be good to look at? A book that applies specifically to the design/repair of solid state amps the way so many books out there do for tube amps? For those of us who took our electronics classes back in the days when they mostly focused on fixing tube devices, that would be good. Not to say I'm so old that we didnt cover the SS stuff, but the tube devices were what I remember "working on" in class and thats what stuck in my head.

[defaced]

Try Teemuk's book on for size: Book about solid-state guitar amplifiers

[jmaf]

One thing, if I may add to the great previous posts: all tubes are depletion mode devices. They conduct maximum current when the grid is at 0 volts, and less and less current as you go negative, down to a certain cutoff voltage that differs for each device. To modulate a signal you must work at some negative grid level and add/subtract from that. If the grid ever goes positive, you can damage the grid and you will definitely not have any signal amplification. This applies to any vacuum tube, due to the physics of electron flow.

Transistors are much more varied, especially since a whole range of devices share the name "transistor".

FETs may be depletion mode or enhancement mode, plus they can be N-channel and P-channel. I can't possibly attempt to summarize all about it, nor my knowledge allows me to. I recommend you search for it, or maybe RG and other transistor magicians can chip in and give us more juicy details about solid state parallels to the tube world.

[defaced]

^I just had to cross that bridge in learning about these kinds of devices and found this site to have a pretty reasonable explanation of the differences and how they work. This particular page goes over the basics, but there two links at the the top of the page for depletion mode and enhancement mode. The Junction FET

[J M Fahey]

Explaining by analogy is good ... to a point ... (I use that all day long) but the differences start creeping in, adding up, and in the long run work against you.
I think you should momentarily forget tubes and start by learning how a single transistor stage works, how it's biased, what its input and output impedance is, how to calculate its gain, how it interacts with the source that is driving it and with the load it drives.
Then how to couple it with *another* stage and what happens in that case.
After you learn that, you can start thinking about it as a "gain block", a black box if you wish, and only *then* you will be able to re-apply your former tube electronics knowledge.
I think it's the fastest and safest way.
Good luck.