Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Merlin on June 21, 2025, 02:20:17 pm
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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!
(https://valvewizard.co.uk/book5.jpg)
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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. :icon_biggrin:
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Covering the whole amplifier ..
Do you mean ALL the aspects
Like Peamp, Power Section & Power Supply ?
Franco
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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)
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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).
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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.
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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
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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.
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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!
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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
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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)
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One other intriguing argument will be: way to have a Tone Control following a pentode preamp stage
Franco
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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.
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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
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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!
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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!!
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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 !
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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)?
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***** 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. :icon_biggrin:
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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!
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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.
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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
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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.).
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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.
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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.
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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.
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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?
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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!
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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?
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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.
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It’s very unlikely those 470k screen resistors are correct.
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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.
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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)
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It’s very unlikely those 470k screen resistors are correct.
Oops,
Yes, they should be 470. Error creating the examples.
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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.
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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!
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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
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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.
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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...
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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!!!
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... Chapter list will be:...
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."
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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
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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
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Here attached the patent of the Varistor vibrato circuit
Franco
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... 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.
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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.
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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?
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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 (https://www.tubesandmore.com/products/guitar-amplifier-overdrive-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.
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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?
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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.
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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 (https://www.aikenamps.com/index.php/white-papers)
Check the other categories as well...
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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.
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After reading Merlin's new book, go grab a copy of "Guitar Amplifier Overdrive: A Visual Tour (http://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.
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I have an intuition that the gain structure of an amp has a lot to do with this. Where does distortion occur?
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.
Your first question is kinda broad, but on the whole I think the new book mostly answers these.
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I have an intuition that the gain structure of an amp has a lot to do with this. Where does distortion occur?
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.
Your first question is kinda broad, but on the whole I think the new book mostly answers these.
Yes... deliberately broad and open-ended, because I don't think there's a single universal answer, and I didn't want to get too long-winded with the question.
In more detail, my questions relate to: at the onset of saturation and distortion, where in the amp does it distort first? And as the signal level continues to increase, where does it distort next? Obviously, this will be affected if there are separate gain and master volume controls, it may also be affected by EQ settings, and some preamps include "cold clipper" stages. What are the characteristics of distortion at different points in the amp? How can the gain structure in a design be manipulated for different styles of playing?
Sorry to create extra work for you - but I think there's another whole chapter of the book implied in this question... or perhaps another whole book!
I have some solid theoretical understanding but I don't have the practical experience designing, modifying, and using as many different amps as the people on this forum collectively have. I want to learn more and so I'll have a lot of (sometimes vague and perhaps ignorant) questions.
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[Edited]
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After reading Merlin's new book, go grab a copy of "Guitar Amplifier Overdrive: A Visual Tour (http://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.)
Fixed.
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.
I'll have to re-read, but it's a book by 2 PhDs... They're covering an advanced topic, and assume the Reader has already connected many dots before they dive in to examine distortion.
There are some results they obtain that naturally follow from the test set-up used, and won't always apply in a guitar amp.
... my questions relate to: at the onset of saturation and distortion, where in the amp does it distort first? And as the signal level continues to increase, where does it distort next? Obviously, this will be affected if there are separate gain and master volume controls ...
The answer changes depending on whether we're talking an amp from the 1950s, an amp from the 1970s, an amp from the 1980s-1990s, or a recent amp.
There have been several-volume works that attempt to dive into the shifting design-trends over decades, from different designers, who leveraged different design approaches. Those different-approaches give a different answer to your one question.
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Where does distortion occur? The preamp (which stage?), phase inverter, power tubes, output transformer saturation?
Yes
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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.)
Fixed.
Thanks for the fixed URL (there's still a couple extraneous characters at the end, but that was easily resolved). I'll add the book to my next order at Antique Electronics Supply.
... my questions relate to: at the onset of saturation and distortion, where in the amp does it distort first? And as the signal level continues to increase, where does it distort next? Obviously, this will be affected if there are separate gain and master volume controls ...
The answer changes depending on whether we're talking an amp from the 1950s, an amp from the 1970s, an amp from the 1980s-1990s, or a recent amp.
There have been several-volume works that attempt to dive into the shifting design-trends over decades, from different designers, who leveraged different design approaches. Those different-approaches give a different answer to your one question.
After I read the first book you referenced, I'll probably want to see the others. It's those shifting design trends I'm curious about.
Thank you!
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Yes... deliberately broad and open-ended, because I don't think there's a single universal answer, and I didn't want to get too long-winded with the question.
In more detail, my questions relate to: at the onset of saturation and distortion, where in the amp does it distort first? And as the signal level continues to increase, where does it distort next? Obviously, this will be affected if there are separate gain and master volume controls, it may also be affected by EQ settings, and some preamps include "cold clipper" stages. What are the characteristics of distortion at different points in the amp? How can the gain structure in a design be manipulated for different styles of playing?
Sorry to create extra work for you - but I think there's another whole chapter of the book implied in this question... or perhaps another whole book!
I have some solid theoretical understanding but I don't have the practical experience designing, modifying, and using as many different amps as the people on this forum collectively have. I want to learn more and so I'll have a lot of (sometimes vague and perhaps ignorant) questions.
The sequence that the stages distort can be designed into the amp, and often some of the best ones distort in the power stage first, and then the phase inverter, and so forth towards the input of the amp. This approach allows for the most touch response.
Greg
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... often some of the best ones distort in the power stage first, and then the phase inverter, and so forth towards the input of the amp. This approach allows for the most touch response.
Thanks, that's very interesting information.
Do you have any examples of "some of the best ones"?
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The Fender 5F6A Bassman does this, and the Marshall amps based on it. I think the Trainwreck amps were designed for same.
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In a competently designed amp, the output stage must clip first. An amp couldn't make full clean power output if a stage prior to the output clipped before it :w2:
Of course any master volume must be turned up full, and other controls set appropriately, to achieve that.
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In a competently designed amp, the output stage must clip first. An amp couldn't make full clean power output if a stage prior to the output clipped before it :w2:
Well, that's a good, pragmatic way to look at it!
I think there's still some interesting territory to explore in the region just before full clipping. The characteristic I like about tube circuits is that they can be designed to saturate (distort the signal a little bit) well before hard clipping (as opposed to typical BJT circuits that tend to be pretty clean and then just slam into the wall). That saturation adds even harmonics and provides a certain amount of compression. When this happens in an earlier stage of amplification, it seems like it should slow the transition into hard clipping in the later stages.
So I would expect the the nature of the transition from saturation into clipping both in the preamp and in the output stage could make a big difference in the overall feel of the amp?
I think I need to get that "Guitar Amplifier Overdrive" book HotBluePlates mentioned....
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Merlin,
So glad you are undertaking this - I've two books of yours, very helpful blend of understandable and some math.
Couple of bits I have struggled with overall (not necessarily because not in your book - just suggestions for topics):
-Keeping track of gain over a circuit
-Estimating node voltages (I made an Excel sheet, still validating)
-Using non-traditional valves in amplifiers (6DX8 for single tube reverb, no transformer, for example?)
-Believe it or not, plans for a chassis holder?
-I can't seem to create good faceplates (at a reasonable price) - Closest I've come is 3d printing one in ABS with raised or sunken letters, painting it then sanding it. All the CAD software I've found has been too steep a learning curve to date. Got a laser engraver - works 'ok' on plexiglass. . .
-Trouble shooting the amp that pops it's circuit breaker after 10 minutes... but not sooner... : ) (causes of excessive current drain you may not have thought about?)
-Toroidal vs. Traditional transformers - design implications and ways to manage them (thermistors?)
Anyway, best wishes, I'll buy whatever you write.
J :m7
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How about the super secret reverb mod you teased at the end of this post?
https://el34world.com/Forum/index.php?topic=31718.msg349548#msg349548
I'd definitely buy that.
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http://www.tubebooks.org/technical_books_online.htm
Franco
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http://www.tubebooks.org/technical_books_online.htm (http://www.tubebooks.org/technical_books_online.htm)
Franco
That’s a real treasure trove. And the some of guys that contributed to it were well known on various guitar tube amp forums until recent years (and have since sadly passed).
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Links not working.
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To me the link performs correctly :w2:
However there you can find good documentation about the basic of tube function, Mr Merlin books are specific to our interests (and I'm waiting for the new book with a lot of interest)
Franco
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I am now close to completing the first draft. Here is the contents list, in case anyone is interested. https://valvewizard.co.uk/contents5.pdf (https://valvewizard.co.uk/contents5.pdf)
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Oh, man... count one copy sold just on the basis of that table of contents (and having found lots of useful information on your website in the past).
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This looks like it will be awesome! Looking forward to the output stage stuff in particular.
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I'm definitely in for a copy - very excited for this new book!
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Will this be hard copy or ebook?
I'm buying either way... Just want to know what I'm buying.
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sign me up too
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Will this be hard copy or ebook?
Hard copy only, same as my other titles.
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I am now close to completing the first draft. Here is the contents list, in case anyone is interested. https://valvewizard.co.uk/contents5.pdf (https://valvewizard.co.uk/contents5.pdf)
Looks very good. :icon_biggrin:
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Hard copy only, same as my other titles.
Excellent! From lifelong habit, I am fond of having a real book that I can sit and read without needed to stare at a screen, put bookmarks in at particularly interesting or relevant places, and of course take care to preserve in good condition.
With that said... I used to buy a lot of O'Reilly computer books back when they were a proper publisher. They offered hard copy, electronic only at a slight discount, or if you bought the hard copy book the e-book was available at a nominal extra cost. I always bought the bundle because there are some advantages to modern technology (it's easy to search a PDF for all mentions of keywords).
If you offered such a bundle, I'd happily pay extra for it. Just saying....
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I noticed that Mixed Bias is covered in the contents — thank you for including it. I find it to be a compelling feature that, when properly applied, can add a unique character to an amp. I'm keen to explore it further
Franco
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I will buy this book to go along with the other two I've purchased from you, Merlin.
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With that said... I used to buy a lot of O'Reilly computer books back when they were a proper publisher. They offered hard copy, electronic only at a slight discount, or if you bought the hard copy book the e-book was available at a nominal extra cost. I always bought the bundle because there are some advantages to modern technology (it's easy to search a PDF for all mentions of keywords).
I got a complete set of John Rider hard covers a few years back for radio repair and knowledge (also as CD). While they have all the info you need (somewhere), it is by far easier to use the internet for info. And now even smarter with AI. If only AI knew how to create a proper schematic. :-)
I also have the Tube Amp Book with all its schematics but still find internet and EL34World my go to.
I love and depend on Valve Wizard and RobRob websites.
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The internet is good, but nothing beats a proper Merlin book! I read them like novels.
I do agree that it would be nice to have a searchable copy, but I bet that would be pirated in a split second . . .
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I do agree that it would be nice to have a searchable copy, but I bet that would be pirated in a split second . . .
Sigh... you're right, of course.
There are ways to personalize PDFs (I have a MISRA C standard document with my name on every page), as well as less obvious ways to watermark them so they can be tracked back to a unique original copy. This isn't an insurmountable obstacle for determined thieves, but it would certainly discourage casual sharing. But I'm sure Merlin has better ways to spend his time than pursuing thousands of small-change pirates all over the world.
AI scraper bots are another matter. But there are ways of "poisoning" various sorts of content so they are worse than useless for AI training.
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Will there be autographed copies available? :worthy1:
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Look forward to reading this. I have got a lot from studying your work. Thankyou.
From my perspective as a newby. I have been studying this subject quite hard for last 8 months and have made some progress in my understanding. Often times I am looking for a simple answer to a question only to find very in depth discussions and explanations going into electronic theory. Whilst I know I need to improve my understanding of this I guess there must be others like me who are simply trying to build the best sounding guitar or bass amp we possibly can, and we are most interested in the outcome. Therefore what I think would be very useful to me and many others would be a "rules of thumb" guidance section. keys things to do or consider to:- reduce noise. increase gain, get the cleanest possible sound, get different flavours of distortion from tubes. what changing the values of components around tubes does to the tone, (most discuss the electrical signal) how does this work in cascading arrangements. There is so much to learn and it is difficult if your starting from scratch with little electrical engineering knowledge.
best
Steve
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I am now close to completing the first draft. Here is the contents list, in case anyone is interested. https://valvewizard.co.uk/contents5.pdf (https://valvewizard.co.uk/contents5.pdf)
I'll be buying the book as usual - I've got all the rest of yours, even the ones you discontinued because you didn't like them. :)
One thing I noticed in the contents list - a typo!
1.2: The Vave Constants
Thought I'd point that out for you....I'm not sure what a Vave is but it sounds risque and not meant for a tube amp book haha.
Greg
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Up until now my books have always been hardback. But with the rise in prices, I'm wondering if I should make this one softback as it would make it at least $10 cheaper. What do people think? Do you want the premium feel of hardback or do you not care and would prefer a cheaper price?
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Happy to pay more for hardback FWIW
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I also prefer an hardback
if not, It would stick out like a sore thumb among the others, which are all hardbacks :icon_biggrin:
No, an hard back will preserve the book from aging for a very long time, this is the reason
Franco
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Please do it in hardback and pages sewn together as on your previous.
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Hardcover please.
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Most of my textbooks from uni are softback and they're fine. Not that they've been consulted much since :laugh:
Whatever, a big price saving is pretty persuasive :icon_biggrin:
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No big preference; equally happy to have the $10 in my pocket as to support those who want the premium kit... but I'm going to buy it no matter what. :)
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I'd like a hardcover to match the other two books of yours that I have. If you made both hard and paperback available, I'll buy both and use the paperback for reading and referencing. Having the set of three in hardcover would just feel right, like buying a matched quad of valves (for an amp that only uses a pair) just before hitting the road.
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...For me: a good hardcover. I prefer this type. Pay more for hardback ( $10 ) it's acceptable.
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Hardback please.
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I vote for hardback to go with your other 2 that I already have.
I'm willing to pay more. That's $10 less inheritance for my kids, so what, :l2:
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I'll buy it either way - but I'd prefer a well-bound hardback.
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Put me down for one - prefer Hardback!
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Well that settles it, I will do hardback as usual. I may offer a softback version aswell, next year.
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hopefully in large print :-)
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hopefully in large print :-)
I'd bet more readers will have gray hair than not :icon_biggrin:
Looking forward to the book, Merlin!