I'm writing a new book - suggestions?

[Merlin]

I'm wiriting a new book: Designing Valve Guitar Amps. [EDIT: This is an evolution and expansion of my preamps book, now covering the whole amplifier. ]
I'm close to finishing a first draft, so I thought I'd ask if there was anything in particular that people might like to see in it. Then I can compare suggestions with what I already have written, and see if I'm way off track or not!

[fossilshark]

The madmans at it again. I'm excited to see what you cook up.

Are more of your book on preamps going to be printed? I just went to go buy it and I see out of print. I already got the power supply bible. 

[kagliostro]

Covering the whole amplifier ..

Do you mean ALL the aspects

Like Peamp, Power Section & Power Supply ?

Franco

[tubeswell]

Output amplifier configurations. SE, PP, Class A B, ultralinear etc and OT types, methods for dealing with control grid current dissipation in little vs big bottles. interplay of screen voltage and control grid voltage on cathode current. All the datasheet techniques for determining output power from load resistance and whatever, different options for negative feedback around the output stage (are a few topics which could make up a chapter)

[stratomaster]

One thing I've always wanted from someone with deep understanding of tube circuits:

Examples of poor engineering used in classic circuits that result in a pleasing tone, and the reasons why it worked--and what the downsides are (reduced tube life, instability under certain conditions, etc) and -- the kicker -- how to get the same/similar effect using proper design methodology (if possible).

[dwinstonwood]

Cool, I'm excited about this project!

...All the datasheet techniques for determining...

I would buy your new book just for clear explanations and examples of how to interpret datasheet numbers. Example: I know what Transconductance is, but what are the tonal differences between two preamp triodes with very different Transconductance numbers? I.e., how do we use datasheet info to guesstimate how "this-tube-over-that-tube" will sound in a circuit. I'm also still very unclear about the relationship between Screen voltage and the rest of a power tube's voltages; even though some very intelligent people have gone to great lengths to explain it. There must be a "key concept" that clarifies the magical power of screens.

[tristanc]

A definitive understanding of the cold clipper and if it really operates as a clipper, or just a lower gain stage. There was an analysis on one of the forums a couple of years back highlighting some gaps:

https://github.com/TomKamphuys/cold-clipper

[tubeswell]

Output amplifier configurations. SE, PP, Class A B, ultralinear etc and OT types, methods for dealing with control grid current dissipation in little vs big bottles. interplay of screen voltage and control grid voltage on cathode current. All the datasheet techniques for determining output power from load resistance and whatever, different options for negative feedback around the output stage (are a few topics which could make up a chapter)

And while I’m thinking about this:-


the different types of output amp distortion, including in different operating classes (crossover distortion etc).


triode vs tetrode/pentode output stages (and other configurations- transformerless valve output stages, SRPP etc  - would cascode driven transformers work?)


Output stages attenuation and line outputs


Field coils


Transformer theory (as it applies to output stages), including effect of interleaving on interwinding capacitance, EMF, back EMF, magnetising current,  primary:secondary winding phase lead/lag


And speaker load, dynamic load vs resistive load, cab design, Thiele parameters etc, which would make a whole ‘nother chapter.

[roarshock]

I already have your preamp book and I'd be happy to have another, more complete off-line resource. I'd love for you to include and expand upon your online reverb and tremolo circuit explanations. Are there any other tube-based effects that you could include? Thanks for sharing your understanding!

[kagliostro]

Assuming the PS will be an argument on the new book

Solid State circuits to supply the Power Sections

Use in Power section where the Power Tubes require a way lower Voltage on G2

----

Variable Voltage Regulators for both Cathode Biased Amps and Fixed Bias Amps

(Some years ago I and a fiend tried to use one of the projects on you books but where not able to have it to work, a search did at that time pointed to impedance  problems due to the Amp circuit or VVR, don't  remember)

----

One other intriguing argument will be: way to have a Tone Control following a pentode preamp stage

Franco

[danhei]

So excited!


As someone with your other books the big missing piece I'd like to see addressed is Power Amps, including the following topics:

• keeping output tubes in a safe operating conditions, e.g., the balance of plate voltage, screen voltage, and output impedance to keep the tube(s) happy
• single-ended
• push-pull
• cathode bias (including individual or shared cathode resistors, plus how to choose the bypass cap value and the impact of very large values)
• fixed bias (including operating within specified maximum control-grid resistance and why so many classic circuits get away with severely exceeding the limit)
• if feasible, ultra-low output power sections*
• maybe ultralinear

* There are a number of designs now for ~1W 12AU7 output sections but it'd be nice to see something that covers true pentode output tone at ~1W (or less) with relatively available tubes. Or maybe something crazy like a 12AU7 cascode output to simulate a very-lower pentode.


And I'm not sure it would fit the brief for this book but I'd also love to see Merlin's take on reactive loads.

[dogburn]

I'm much more a beginner than a lot of these other guys, but what I would find helpful would be:
- how to calculate the impedance an amp requires for an output transformer
- how to calculate the effects of dropping resistors on power supply

[pdf64]

Topics that raise their head when designing  / implementing a whole 'new' amp include -
Achieving / maintaining stability, especially as system gain is increased.
How OT impedance plays into power amp current draw.
How power amp / DC current draw relates to AC current in the mains transformer's HT winding (2 phase and FWB rectification), and, with 2 phase rectification, how that relates to the winding's current rating.

This could be a big book!

[elams1894]

Achieving / maintaining stability, especially as system gain is increased.

I second this suggestion by PDF64. Anything regarding ensuring stability as preamp gain is increased, eg 4, 5, 6 gain stages. Especially so for output tubes, for example with EL84's in which stability is difficult to achieve.

Thanks for all that you do, much appreciated!!

[acheld]

I'd be interested in a discussion of how Dumble overdrive circuits work -- they are so different in tone than Marshall.  And while I build them, I can't truly say I understand them.

Lots of good suggestions here !

[jojokeo]

Achieving / maintaining stability, especially as system gain is increased.

I second this suggestion by PDF64. Anything regarding ensuring stability as preamp gain is increased, eg 4, 5, 6 gain stages. Especially so for output tubes, for example with EL84's in which stability is difficult to achieve.

Thanks for all that you do, much appreciated!!

I don't think this is a big mystery achieving "stability in cascaded gain stages" - it comes down to proper grounding, obvious layout placements (not too close to the power section), and then the use of voltage dividers and grid stoppers, not sharing too many B+ nodes, etc. Designing your amp with these types of things in mind ahead of time will save TONS of time troubleshooting & frustrations later on the back end.


***Merlin has mostly adressed what I said above in his books - BUT: I've often wondered how to determine which B+ NODES can be shared and which can NOT be shared and why? How to predict and design B+ NODES effectively (in this context)?

[Lectroid]

***** for the new book.

All of these ideas are worth including, absolutely.  But I would specifically like to see some more of the sorts of tips, tricks, and techniques known and used by the more truly knowledgable builders who've received some flavor of institutional education in electronics--at trade school, military education classes, community colleges, etc.

Any tips, tricks, or rules of thumb, etc., would be useful--anything the self-taught might not know.  Many of us who've had a more systematic education might well find them second-nature and elementary, but being self-taught, I find those digressions and anecdotes really valuable. 

Anyway, as to what all the others said, that stuff too.   

[Merlin]

Some good suggestions, thanks guys. Quite a few of them I have already got covered, so that's good, and some others I will clarify with some extra sentences.
Cascodes, however, will not be included. I have removed them altogether -they're just not used in guitar amps. VVRs will also not be included, as they're in my Power Supplies book.Chapter list will be:

• The Triode Gain Stage
• More Preamp Essentials
• Tone Stacks
• The Cathode Follower
• The Pentode Gain Stage
• The Cathodyne Phase Inverter
• The Long-Tailed-Pair
• Tremolo
• Spring Reverb
• Single-Ended Power Stages
• Push-Pull Power Stages
• The Power Supply
• Signal Switching
• Layout and Grounding

EDIT: Field coils?? I think you need a book on vintage radios!

[tristanc]

If I could make one more suggestion - it would be useful to expand on section 14.3 in the existing preamp book; the steps for voicing and dialling in your target sound. I know it’d be very subjective, but perhaps could be of benefit for those not wanting to copy existing designs. Perhaps a longer worked example and maybe including sound samples at each stage of development on your website? Maybe some overlap with Richard Kuehnel’s books, but with your take could be useful.

Oh, and a huge thing that I now appreciate that I didn’t before (and maybe something to put in big letters at various stages): DON’T FORGET THE IMPACT OF THE SPEAKER

Many hours lost chasing unwanted fizz / honk / nasal etc, messing with bypass caps, bias points etc when a swap in speaker likely had a more desirable impact.

[kagliostro]

14. Layout and grounding

I was near to ask for it but I thinked that layout planning is a big argument, very happy to read you will afford the argument

Franco

[tristanc]

14. Layout and grounding

I was near to ask for it but I thinked that layout planning is a big argument, very happy to read you will afford the argument

Franco

+1

Also, since much of the Gothik Ring stuff has disappeared from the internet (AX84, Mason Atom etc) perhaps a summary of that approach to P2P? And maybe a discussion on construction techniques (turret, tag, PCB, hybrid, e.g.).

[passaloutre]

Some good suggestions, thanks guys. Quite a few of them I have already got covered, so that's good, and some others I will clarify with some extra sentences.
Cascodes, however, will not be included. I have removed them altogether -they're just not used in guitar amps. VVRs will also not be included, as they're in my Power Supplies book.Chapter list will be:

• The Triode Gain Stage
• More Preamp Essentials
• Tone Stacks
• The Cathode Follower
• The Pentode Gain Stage
• The Cathodyne Phase Inverter
• The Long-Tailed-Pair
• Tremolo
• Spring Reverb
• Single-Ended Power Stages
• Push-Pull Power Stages
• The Power Supply
• Signal Switching
• Layout and Grounding

Maybe I'm a little biased (ha!) because some of my favorite designs have them, but if you're going to include LTP and Cathodyne PI circuits, why not the Paraphase and the self-balanced version?

In the Tremolo discussion, could you discuss the Fender Harmonic Tremolo (which can include a self-balanced paraphase and/or cathodyne) and (e.g. Vox's) frequency-modulating vibrato? Maybe also which types of tremolo require buffering/cathode followers?

And since we're in the 21st century, I'd love to see some discussion of where and how to use mosfets to augment tube designs, e.g. as buffers, gain stages, and oscillators.

PS, I love your books and your site! Both are kept near-at-hand every time I'm working on anything tube-related.

[Merlin]

if you're going to include LTP and Cathodyne PI circuits, why not the Paraphase and the self-balanced version?

Hmm, good point. I won't make it a chapter of its own, as it's not really different from a regular gain stage, but I can shoehorn it in, in a section I have about local shunt feedback.

In the Tremolo discussion, could you discuss the Fender Harmonic Tremolo (which can include a self-balanced paraphase and/or cathodyne) and (e.g. Vox's) frequency-modulating vibrato?

I didn't include that as it really needs its own chapter beyond tremolo, and very few amps ever used it - this book is focused on 'normal' amplifiers with common features. But I guess I could write a chapter on it at a later date and make it a web exclusive article.

[Merlin]

I've often wondered how to determine which B+ NODES can be shared and which can NOT be shared and why? How to predict and design B+ NODES effectively (in this context)?

I'm not sure what you mean. The B+ nodes follow the signal path. You wouldn't want a very late stage sharing the same node as a very early stage.

[Merlin]

I'd be interested in a discussion of how Dumble overdrive circuits work

There are several Dumble schematics floating around, but they all look fairly normal IIRC. What is puzzling you?

[jojokeo]

I've often wondered how to determine which B+ NODES can be shared and which can NOT be shared and why? How to predict and design B+ NODES effectively (in this context)?

I'm not sure what you mean. The B+ nodes follow the signal path. You wouldn't want a very late stage sharing the same node as a very early stage.

Thank you for considering and I'll try to explain by example. I've seen two tubes / 4 gain stages all use the same B+ node while most others - each 12ax7 has it's own B+ node. While there's other designs where it's okay for a triode stage to also be connected to an earlier tremolo node in the circuit. But, the main idea is that there's no hard and fast way to understand or know ahead of time if certain pre-amp gain stages can be combined onto the same B+ node or not? I've used a Soldano circuit for an example:
Thank you Merlin!

[jjasilli]

Some good suggestions, thanks guys. Quite a few of them I have already got covered, so that's good, and some others I will clarify with some extra sentences.
Cascodes, however, will not be included. I have removed them altogether -they're just not used in guitar amps. VVRs will also not be included, as they're in my Power Supplies book.Chapter list will be:

• The Triode Gain Stage
• More Preamp Essentials
• Tone Stacks
• The Cathode Follower
• The Pentode Gain Stage
• The Cathodyne Phase Inverter
• The Long-Tailed-Pair
• Tremolo
• Spring Reverb
• Single-Ended Power Stages
• Push-Pull Power Stages
• The Power Supply
• Signal Switching
• Layout and Grounding

EDIT: Field coils?? I think you need a book on vintage radios!

Merlin, looks like you've got this covered.


Don't know if you're interested, but, going out on a limb here, what about switching power supplies to eliminate a PT?

[RoadShow]

Hi,

I'd like a better understanding for how the screen and grid resistors are chosen for 6L6GC/KT66, EL34, etc. in the power section and why they're necessary.  I understand in the simplist way, but would like a better understanding.
Is there a fudge factor in the selection or need?

Note the examples in the attachment.  There doesn't seem to be a standard design per se.

Thanks.

[passaloutre]

It’s very unlikely those 470k screen resistors are correct.

[Merlin]

I'd like a better understanding for how the screen and grid resistors are chosen for 6L6GC/KT66, EL34, etc. in the power section and why they're necessary.  I understand in the simplist way, but would like a better understanding.
Is there a fudge factor in the selection or need?
Note the examples in the attachment.  There doesn't seem to be a standard design per se.

The standard is 470R to 1k (470k is a typo). There's no 'correct' value, but I show the effect of the stopper on screen dissipation, in the book.

[Merlin]

I've seen two tubes / 4 gain stages all use the same B+ node while most others - each 12ax7 has it's own B+ node.

Two tubes is what Fender did to save money, when caps were expensive. These days we use one tube per node, except for vintage Fender copies of course.
The Soldano is an odd one, I suspect it is accidental rather than deliberate. Maybe it was easier to lay out, or maybe it was just a wiring goof in the prototype, which they decided to leave as it is. Or maybe it's a drawing error (I can see a drawing error in that diagram on the loop recovery stage, so maybe it's not the only one)

[RoadShow]

It’s very unlikely those 470k screen resistors are correct.

Oops,

Yes, they should be 470.  Error creating the examples.

[acheld]

I'd be interested in a discussion of how Dumble overdrive circuits work

There are several Dumble schematics floating around, but they all look fairly normal IIRC. What is puzzling you?

I guess my only real question is: what is the role of plate to cathode capacitors?   How to voice them with a better understanding of what they do.

I would much rather read your explanation for this than work my way through an LTSpice simulation.   The simulation works better if you (really) know what you're doing. 

[Merlin]

I guess my only real question is: what is the role of plate to cathode capacitors?   

Oh they just shunt treble, like any shunt capacitor. They create an RC filter with the tube's output impedance (about 40k). I have added this to Chapter 2!

[SoundmasterG]

One thing I thought of that might be of interest would be a short explanation of what happens to the power output, distortion level, and sound if you change the primary  impedance of the output transformer, but keep the tubes and voltages the same. Example would be say a standard 6L6GC pair, 50 watts like in many vintage amps, and the speaker is always on an 8 ohm tap. What happens if the stock impedance is say 6600 ohms and you adjust that to 4000 ohms in one example and 8000 ohms in another. Might help people to understand more about what the sound and power might be when they go to pick a transformer, and why you might want something different.


I second the addition of the paraphase inverter types too. Some well respected vintage amps from Supro (Thunderbolt), Fender (many tweed amps), and Vox (AC100) used either the paraphase or floating paraphase and there are distinct pros and cons with using all the different types of inverters. Knowing what advantages and disadvantages of various circuits helps the people who may want to design parts of their amp projects rather than just copy vintage circuits like some do.


I'll be ready to purchase once you new book is available. All your other books have been great! Thanks for taking the time to write them and vet everything in them!


Greg

[HotBluePlates]

I'm writing a new book: Designing Valve Guitar Amps. ...

...Chapter list will be:

• The Triode Gain Stage
• More Preamp Essentials
• Tone Stacks
• The Cathode Follower
• The Pentode Gain Stage
• The Cathodyne Phase Inverter
• The Long-Tailed-Pair
• Tremolo
• Spring Reverb
• Single-Ended Power Stages
• Push-Pull Power Stages
• The Power Supply
• Signal Switching
• Layout and Grounding

The Chapter list appears to proceed from "Input Jack" to "Power Section," 'Power Supply" and "Physical Construction."  It seems many readers find this "follow the signal path" sequence easier to grasp.

However, when actually designing from the ground-up, we usually need to start with choices about "how loud" and "which speaker(s)," and then proceed to choices around Power Section Topology and available power & output transformers.  "Working backwards" from Speaker to Input Jack causes each completed section to define the requirements of the section that is designed after, but electrically precedes it.

I've seen a number of folks paint themselves into corners because the books they read presented material in the "Input Jack to Power Section" order, and it was not clear to them that a practical design is easier in the reverse direction.

[Merlin]

I've seen a number of folks paint themselves into corners because the books they read presented material in the "Input Jack to Power Section" order, and it was not clear to them that a practical design is easier in the reverse direction.

Very true. Starting with preamp chapters is kinda inevitable because they tend to be easier to comprehend to start with, but I do make the point in the book, that design really starts with the power supply/output stage. Hopefully if people read cover to cover, they will come away with the broad system knowledge. Hopefully...

[shooter]

maybe after the last page of design understanding a quick n dirty on "stage testing", Ie; the PS under a calculated load, after ohms checking the obvious goes a long way to eliminating rabbit holes before the full amps built;.... with no sound, as smoke rises from all the new shiny, perfectly positioned components.



along HBP's working backwards stages, PS tested n good??..Yep, PA dcv good?...Yep...add line level AC, speaker....


once you understand the amps design, doesn't get you a killer amp, without a "logic process" from "everyone says it'll work on paper" to ...It does work!!!

[HotBluePlates]

... Chapter list will be:

• Push-Pull Power Stages

...

Perhaps you had this planned:

In the past few days I've had to re-write on forums about how a push-pull amp might have been designed for a cooler bias than is currently fashionable.  Further back, I've had to write about why a given output tube type doesn't "want a particular OT primary impedance" but that it's a function of the ratio of voltages & current used in that design to hit a particular power output target.

I think it would be instructive to use a single tube type (maybe 6L6GC or EL34), and show perhaps 3 different designs:  a 250v plate & screen Class A design, a low-power Class AB design with 400v plate and maybe 350v screen, and a high power Class AB (close to Class B) design with 475v plate & screen (or higher).  Juggle the voltage figures as necessary to demonstrate that:

   - OT Primary Impedance changes depending on available supply voltage, and output tube peak plate current capability.

   - Idle bias changes when supply volts and peak plate current go up, because:

       1) the tube needs to shut off longer to prevent overheating, and
       2) Large variational plate current divide by Gm implies a large AC drive signal to achieve higher power outputs.

A lot of books describe the basics of the Power Output section, but not many connect the dots to explain that
"No, that maker didn't 'bias too cold,' they set up their output stage to deliver high power."

[tubeswell]

In the Tremolo discussion, could you discuss the Fender Harmonic Tremolo (which can include a self-balanced paraphase and/or cathodyne) and (e.g. Vox's) frequency-modulating vibrato?

I didn't include that as it really needs its own chapter beyond tremolo, and very few amps ever used it - this book is focused on 'normal' amplifiers with common features. But I guess I could write a chapter on it at a later date and make it a web exclusive article.

And other types of wobbly signal stuff like how varistors work in Magnatone Amps and the ‘vibrato’ in Vox amps

[kagliostro]

Some time ago Martin Manning developed a sub for those old varistors but seems that the necessary components nowadays are to be considered obsolete and difficult (or, maybe, impossible) to be find

EDIT: OK, seems that now the components are available but the interest persists

So, if Magnatone amp will be discussed it will be very interesting for a circuit able to sub the original varistors

---

Here attached the patent of the Varistor vibrato circuit

Franco

[pdf64]

... the ‘vibrato’ in Vox amps

My understanding is that the Wurlizter etc vibrato really is vibrato, that phase modulation and frequency modulation are 2 sides of the same coin.

[scstill]

Sorry if this was already mentioned and if I missed it.

But will this book be available as online text as well as in print?
I find that that valvewizard.com is extremely valuable when I need it.

Will this new book be in addition to Valvewizard.com or (assuming same Merlin) will Valvewizard.com be revised? Might be confusing if two sources.

[rumpus]

I'm wiriting a new book: Designing Valve Guitar Amps. [EDIT: This is an evolution and expansion of my preamps book, now covering the whole amplifier. ]
I'm close to finishing a first draft, so I thought I'd ask if there was anything in particular that people might like to see in it.

I finally got motivated to register here (after thinking about it for quite a while) because there are a couple things I'd be very interested in seeing in your new book.

I play bass, through a tube amp whenever possible. I like tube amps because of the magic that happens at the edge of saturation and distortion. Different amp designs reveal very different characters when pushed this way. One of my favorites to hear is the old Fender Showman (Phil Lesh, Jack Casady, and Chris Squire all used these early on).

I have an intuition that the gain structure of an amp has a lot to do with this. Where does distortion occur? The preamp (which stage?), phase inverter, power tubes, output transformer saturation? I think perhaps the whole is more than the sum of the parts... what's really going on here? Illustrating this with some analysis of classic amps might be informative.

The other topic I'd like to see more about is choosing an appropriate primary impedance for the output transformer in a push-pull output stage. Because the speaker impedance varies so much with frequency, I would expect a certain amount of compromise to be necessary. A good match for maximum power out at one frequency could a very poor mismatch at other frequencies. What effect does negative feedback have on the choice?

[HotBluePlates]

Where does distortion occur? The preamp (which stage?), phase inverter, power tubes, output transformer saturation? I think perhaps the whole is more than the sum of the parts... what's really going on here?

After reading Merlin's new book, go grab a copy of "Guitar Amplifier Overdrive: A Visual Tour."

That book addresses your questions, but you will very likely still want to read Merlin's book first:  the book above assumes the reader has a pretty good knowledge of amplifier building blocks & design.  You will get more out of it after gaining a solid grasp of the foundational issues.

[passaloutre]

While we’re on the topic, are there any other books people could recommend me for some summer reading? I have Merlin’s preamp book, the Jack Darr book, the RCA handbook…I definitely absorb more every time I reread them, but I might be ready for a new perspective, or something a little more advanced. I would love to find something similar to what HBP was describing above, with designing power amps around different parameters. Are the Keuhnel books good? Pittman? Megantz?

[Merlin]

While we’re on the topic, are there any other books people could recommend me for some summer reading?

High-end Valve Amplifiers 2 by Menno Van der Veen is good. I think it has only a chapter on guitar amps, but for general power amp theory it's a nice addition to the library.

[jojokeo]

While we’re on the topic, are there any other books people could recommend me for some summer reading? I have Merlin’s preamp book, the Jack Darr book, the RCA handbook…I definitely absorb more every time I reread them, but I might be ready for a new perspective, or something a little more advanced. I would love to find something similar to what HBP was describing above, with designing power amps around different parameters. Are the Keuhnel books good? Pittman? Megantz?

White Papers
Check the other categories as well...

[rumpus]

While we’re on the topic, are there any other books people could recommend me for some summer reading?

The classic work is the Radiotron Designer's Handbook. I think you can download a scan from http://www.tubebooks.org/. It's not exactly light summer reading, though.

[rumpus]

After reading Merlin's new book, go grab a copy of "Guitar Amplifier Overdrive: A Visual Tour."

That book addresses your questions, but you will very likely still want to read Merlin's book first:  the book above assumes the reader has a pretty good knowledge of amplifier building blocks & design.  You will get more out of it after gaining a solid grasp of the foundational issues.

I'll go looking for that. (The URL isn't actually a URL, but I bet a web search will find it from the title.)

I have a fairly good grasp of the foundational issues. What I'm lacking (and hoping to learn from this forum) is the practical knowledge that's not immediately evident from just knowing theory.