Forum Project: Design and Build Tube Amplifier

[randyc]

In the following thread, I floated an idea about a forum project: designing and building a vacuum tube amplifier, much like the one discussed here:

http://www.jazzguitar.be/forum/guitar-amps-gizmos/10263-small-tube-amp-reccomendations.html

For some time I have considered designing a small amplifier - in the power range Mr. Beaumont described as desirable - but in "push-pull" configuration (unlike the "Champ"), using inexpensive, power-efficient vacuum tubes. The musical objective would be to replicate the tonal characteristics of larger amplifiers without the commensurate increase in cost and weight (and obviously lacking in loudness). A "line output" might be a desirable feature, maybe an effects loop ... just thinking out loud.

In past posts, I've suggested that forum members might collectively perform a project like this one. Recognizing that most do not have metalworking machinery, design experience, electronic test equipment and other barriers that might prevent a "design-to-finished-product" goal, it may be possible to assign certain design tasks to various members (no special equipment requirements) and actually produce an amplifier to a set of pre-determined design goals.

(Recall that these amplifiers, boutique and otherwise, are copies of copies of copies - vacuum tube amplifiers are primitive examples of electronic design albeit desirable ones, for many of us. The skills involved are not sophisticated - simple algebra and common sense gets one through most of the vacuum tube amplifier design process. Download the free book if you're interested in the history and design process of these products. I'll post it again soon ... still tinkering with the verbiage.)

In other words, with some design input and with guidance/management, well ... starting to get the idea? Documenting the various steps of making a small amplifier; it's not difficult. Manufacturers of musical equipment would have us believe otherwise, LOL. A forum project - sort of similar to the product evaluations that we've done recently. The exercise could be "subsidized" by free labor and equipment capacity. Think about shared cost effectiveness, the ability of members' capability to make parts of the amplifier. Even if the project did not progress to conclusion, an interesting and entertaining learning experience would be documented.

So ... health permitting, I'm willing to manage the project, guide voluntary participants in individual tasks, evaluate and correct designs of the various stages and produce whatever hardware and woodworking is required. The end result would be that a single member possesses the amplifier and the obvious questions might be "who pays" and "how much" ?

If we assume that our labor is "free" then materials and shipping are the only cost. If there is interest in the project then I can underwrite it financially. The "owner" of the completed amplifier can be determined by various means by the participants but would only be required to pay for materials.

Although I haven't spent more than a few minutes considering the project, it could be broken down so that many individuals participate and are responsible for specific tasks, perhaps like the following list. Incidentally, I'm thinking that Mr. Beaumont would be the logical choice for the first two assignments … if he cares to participate.

Establish design goals and preliminary specifications:

Loudspeaker goals and selection:

Power amplifier design, including output transformer selection, from specifications:

Phase-splitter design, from specifications:

Tone control, volume control and post-amplifier design, from specifications:

Preamplifier design, from specifications:

Power supply design, from specifications:

Amplifier chassis mechanical layout and fabrication (metalworking skills and machinery required):

Amplifier enclosure layout and fabrication: woodworking skills and machinery required

Amplifier electrical assembly:

Amplifier unpowered electrical continuity test:

Power supply electrical assembly:

Power supply electrical test:

Complete amplifier integration and test:

I would be available to consult by e-mail or telephone on any phase of the project and if there is a lack of volunteers in certain areas, I can assume those responsibilities. We would be working from the appropriate chapters of my vacuum tube amplifier design book - I'll provide the latest version for free download soon. (This will allow the opportunity to correct any errors in the text with real design examples.)

There are also available, software design tools for many of the details, as well as lists of preferred parts from which selections can be made. If there is interest in the project and as responsibilities are defined, I'll e-mail the design tools (they are in the form of Excel spreadsheets).

"Deliverables" would be required at important steps of the design, fabrication, assembly and test processes. These can be established in detail later but might, for example, consist of design notes, completed spreadsheets, digital photographs and so forth.

Please let me know if you are interested.

Thanks,
Randy

[derek]

I am very interested, as we have batted around an idea like this before, but unfortunately, other than a few bucks and moral support, I wouldn't have much to contribute. With no skills in this area, I would be pretty worthless, but oh so curious about the process.

[bkdavidson]

I could pretty much copy and paste Derek's reply for myself. In the very near future, I will learn how to use a soldering iron, though. My 'Lil Orphan Annie' guitar, which is the red Ibanez I found in the trash at my apartment, is getting a new neck pickup soon. I WILL learn how to install a pickup.

[gpmedium]

As I said in the other thread, I'm very interested in the project and would like to contribute my meager skills.

[randyc]

Hi Derek (and others),

There are a number of reasons for doing this but the most important one is education. Although some basic knowledge of electronics is useful, vacuum tube amplifiers can (and are) built by people with little experience of the subject but have the desire to learn and are reasonably intelligent.

Almost any member of this forum has the capability to contribute if the motivation and TIME exists. I've never read a single post on this forum that would make me think that the member wasn't above average intelligence.

For those that aren't necessarily interested in learning the electronic details, there are plenty of other jobs. If one isn't a woodworker or a machinist, there are organizational details that should be addressed such as coordinating schedules, arranging for photos of the work in progress, design details, parts selection reasoning and collecting all of the data required for preparation of progress reports for the membership to read.

Those who are not direct participants will want to visualize how the entire design and manufacturing processes work. It will take some clever individuals with good writing skills to prepare periodic presentations of the various efforts so that everyone understands what is being done and WHY it is being done a certain way.

If the intent was simply to construct an amplifier, I could bang one out in a couple of days, photographing various stages of the work (like I did eight or nine months ago, when I posted my "Mini-Bassman" amplifier). But that doesn't directly involve anyone and teaches nothing.

If this effort gets off the ground, it's going to be a long-term project, due to the long-distance communications problems and the individual reviews and corrections that will inevitably be required. It may be so lengthy that readers lose interest, who knows? At the moment, my intuition suggests that the entire effort can be completed in two months but that doesn't account for how much supervision of the various efforts will be required.

Thanks for the offer of some financial support but I can handle that. I'd like to eventually recover my costs for parts and shipping but that's not really necessary either if people learn something from the project .

Maybe I should approach this differently by asking of those who are interested to advise me of how/what they can contribute.

Certainly there are opinions, for example, of what kind of parts (like the loudspeaker) might be appropriate. A valuable contribution might be for a member to prepare a checklist of what people consider important for this device and conduct sample surveys to get a consensus of what constitutes a desirable part. Just a thought ...

Same thing would apply to the general specifications of the amplifier. We have a target goal for the output power level (around 5 watts) but what about the tone control/EQ capability? Fender configuration? Other features that aren't included in the three-control EQ?

These things would have to be evaluated by someone to determine what the actual specifications should be. An experienced, knowledgeable guitarist with a background that includes various amplifiers or a committee of such people. There's room for a lot of contributors to participate, even if the participation doesn't include building hardware.

There's a reason that there are scores of boutique vacuum tube amplifier makers and zero boutique solid-state amplifier makers. Vacuum tube amplifiers are simple devices - nothing intimidating about designing one. I'll get the design book ready for downloading again real soon ... people can refresh their memories about the various stages, what they perform and some of the important features of each one.

In the meantime, interested persons can volunteer for specific tasks outlined in my first post or express a willingness to help along with your personal skills that can move the project along. We have two volunteers that are interested in the circuit aspects already. I'll wait a few days for more responses and then present the outline again, hopefully this time with some names "pencilled in" for some of the assignments.

Cheers,
Randy

PS: Remember that I can consult with any individual responsible for any part of the process, one-on-one. We can do that by e-mail or telephone, exchanging schematics, drawings, whatever is necessary to transmit ideas and suggestions. We should conduct this on a professional level which will include a preliminary design review to be scheduled once we have filled in the assignments.

[randyc]

Here's the link to download the vacuum tube book:

https://acrobat.com/#d=UjgTcfpvfqvboIiQLKn5rQ

[goshawk]

I'd certainly like to be involved. I have no electronics background, but I have modded a Valve Jr., so I have a little experience reading a schematic and soldering/unsoldering components. I'd love to try my hand at design, perhaps of the pre-amp, or perhaps doing the assembly.

More realistically, I make my living as a writer, so I could certainly step in and help out with anything that needed to be done there.

[randyc]

Jim and others:

If the premise of my book is correct, the required credentials of a vacuum tube designer are minimal. Some knowledge of basic electronics, a good mind, motivation, ninth-grade algebra and a pocket calculator should be adequate to get through a project like this one.

Try downloading the book (it's over 300 pages, so it might take a few minutes), skip the historical introductory stuff and start at chapter 2. Read for an hour or so and see if you are comfortable with the concepts - might have to read some of the paragraphs a couple of times.

If you feel that you're "getting it", then you are 90% there and with guidance, can do useful design work. If confused after giving the reading a fair try, then there are numerous other support chores that will need coverage if this is going to be truly useful to the general forum membership.

I tried to present a step-by-step design methodology in the book but didn't actually have a project at the time to photograph and document. This might be a good way of demonstrating the process to the readers here ...

There doesn't seem to be an excess of volunteers at the moment but for those that are truly motivated, we might still do some useful work by assigning the design tasks, offering suggestions and even performing computer performance simulations. We'll wait for a few days and see what mtranspires.

Cheers,
Randy

[billkath]

If you decide to build a speaker cabinet, I'd be happy to give you some scans in pdf about acoustics, as long as they weren't shared outside of the group. Leo Beraneks book in particular has some great stuff on enclosures that might be very helpful to you. Just shout if you need it.

[bkdavidson]

Actually, I've replaced the pre-amp tubes in my Marshall. So I have done something to a tube amp at one point. In all seriousness, though, I'd like to learn how to do this. Right behind my dream of someday building my own guitar is building an amp. As far as speakers, I'd like to throw Tone Tubbby speakers out there HempCone - Abrown, ToneTubby, Hemptone, GreenThunder a bit pricey, but they sound amazing. I have one in my Marshall. They have a very deep, warm, smooth tone and make the amp sound a lot bigger than it is. It seems they get overlooked a lot.

[randyc]

Download book.
Read for an hour.
Let me know your thoughts not about the book but about how YOU can contribute to the project.

Randy

[goshawk]

I've downloaded the book and I'll make some time this weekend to start reading.

[bkdavidson]

I started reading the book as well and might be of some actual help. It made sense to me. Hopefully, within a week to 10 days I'll have received the replacement pickup for my guitar, swapped it out, and will know if I can really use a soldering iron or not.

[gpmedium]

I've downloaded the book as well.

I'm up for the electrical assembly and testing and I would certainly be interested in being involved in hashing out the design parts, and hearing the pros and cons of each as I view this as a great chance to learn more about this type of electronics.

[BigDaddyLoveHandles]

Will there be reverb?

And more importantly, what will you call it?

[randyc]

No effects - the design will be predicated on the post Mr. Beaumont started on small amplifiers. It will be called whatever the eventual owner chooses to call it. (Although since the design might be loosely based on a push-pull version of the Fender "Champ", the working name could be the "Chump".)

Cheers

[BigDaddyLoveHandles]

I wasn't going to be so cruel! In the link to the compendium of small amps that Derek posted:

Low wattage guitar amplifiers, amps 1, 2,3, 5, 6, 7 , 10 watts.

I see there is a ...

[philipmgibson]

I've contemplated building a tube amp from scratch in the past, but the killer to these projects is always the transformers particulary the impedance matching output transformer.There are very few of these commercially produced any more getting laminations stamped for a one off is prohibitively expensive. Also handwinding transformers if very painstaking if you are to avoid loose winding rattling (In the long term loose winding are also prone to shorting) If you are prepared to stick to 20W there are mains and outpt transformers available from Maplin athough these restricts your design considersably.

[BigDaddyLoveHandles]

Originally Posted by philipmgibson

I've contemplated building a tube amp from scratch in the past, but the killer to these projects is always the transformers

I know zilch about electronics, but I've read lots of good things about Weber. Have you checked them out?

https://taweber.powweb.com/store/magnetic.htm

[randyc]

Originally Posted by philipmgibson

I've contemplated building a tube amp from scratch in the past, but the killer to these projects is always the transformers particulary the impedance matching output transformer.There are very few of these commercially produced any more getting laminations stamped for a one off is prohibitively expensive. Also handwinding transformers if very painstaking if you are to avoid loose winding rattling (In the long term loose winding are also prone to shorting) If you are prepared to stick to 20W there are mains and outpt transformers available from Maplin athough these restricts your design considersably.

Not a problem at all. Download the book to see how to select the transformers. If you feel comfortable about the material, there is a full set of spreadsheets available for amplifier design with lists of both power supply and output transformers that are readily available.

In one chapter of the book, there is a full discussion about how to tailor the selection and bias conditions of the output tubes to match an available transformer.

Cheers

[goshawk]

Unfortunately, time prevented me from getting as far into the book this weekend as I wanted. What I did read was challenging, but understandable, so I'm still in.

[philipmgibson]

Thanks to BigDaddyLove handles for the Weber link. Man you know a lot of stuff, you're a one stop knowledge shop!!
Must admit it's been a few years since I've contemplated a valve amp,(pre internet days) and I've never really searched the net for the resources.
Lots of good stuff on that site at very reasonable prices, with what's there you could cook up pretty much anything you'd like.
I'd love to apply my soldering iron to a project like this. I worked as a wireman/electronics assembler on military radar systems years ago. But sadly I'm on ther other side of the pond to you guys.
But with that link you might have just resurected an old dream...

[randyc]

Philip, there are many, many sources of parts for this type of equipment in the U.S. - easily located by internet search ... one of my favorites is "Antique Electronic Supply".

They stock many varieties and types of transformers and for me, the most valuable resource is the huge inventory of NOS vacuum tubes at incredibly good prices. If you are in Britain, of course you will be burdened with shipping costs and VAT but surely there are similar suppliers in Europe ...

There is a "cottage industry" of garage and bedroom operations where people equipped with a surplus tube tester match output tubes (usually at a premium cost) and wind transformers for custom applications. Not to mention the so-called "boutique" amplifier operations, where people reproduce old Fender (and other) amplifiers in different packaging.

I'm constantly surprised not to read about similar efforts in Europe, since this is a European forum and the level of interest there is certainly not less than that in the U.S. If you can shed any light on this I'd certainly enjoy learning about the lack of "home-grown" products over there - if, in fact, there IS a lack.

Cheers,
Randy

[philipmgibson]

Like I said it has been a long time, almost 20 years, since I first looked into this, and the market for this type of thing seems to have increased greatly in the intervening period.

I just had a quick look for businesses in the UK supplying valve amp transformers I don't want to name names in a public forum but those that I found that were quoting prices online varied from around 100 to 400 GB pounds that's 150 to 600 US dollars for items Weber had for well under a hundred dollars.

I think the problem is largely one of scale, the population of the US is about 6 times that of the UK. If you have a dozen businesses in a particular sector we might have 2 and the laws of supply and demand do the the rest.

Additionaly having spent a little time in the US I think you would find it hard to believe how much more service oriented your culture is compared with ours. If you call up a US based company as an individual looking for a product or service they will almost always be prepared to bend over backwards to help you. In the UK unless you're calling with a massive order they just don't want to know.

[randyc]

Thanks, Phillip - the scale presumption seems likely to me.

Following the general thoughts of this thread, we could perform a simple experiment regarding cost and availability of components that you may previously have regarded as uncommon.

First, you might download my book and read the section about output stage and output transformer design/selection (mostly in Chapter 8 but fine-tuned in parts of Chapter 16).

Let's divert briefly... One might question why I continue to mention the book when there is no financial motivation (it's free) but there is a practical motivation. The book has never been peer-reviewed. I've asked a number of colleagues to do so but they beg off, pleading lack of education on the subject or lack of time. So there may well be errors that are unapparent to me (the forest and tree thing).

I've made the text available to several forums, requesting comments. Got a few but not many. So, one of the motivations for a forum design/construction project was to test my communications ability to those who are interested in this type of project but are not as technically inclined as some of us.

OK, done with that and getting back on track, here's my suggestion. Complete the design procedure of the output stage in Chapter 8, including the selection of the transformer. Make the online selection/order process (NOT actually placing the order, of course) and let us know the actual cost if ordering a transformer (as an example) from the U.S. and delivered to the U.K.

A few months ago, a similar exercise was performed regarding Gibson archtops available in Europe and the results were surprising.

Cheers,
RandyC

[randyc]

Originally Posted by goshawk

Unfortunately, time prevented me from getting as far into the book this weekend as I wanted. What I did read was challenging, but understandable, so I'm still in.

Appreciate your enthusiasm !! The project has about three interested persons at this point so it will probably fizzle out.

I'm conducting an experiment: I belong to several machinist, woodworking and engineering forums. Many of the members of those organizations are also guitarists (LOL - every third male I meet is a guitarist). I posted the link for the amplifier design download on one of the machinist forums today.

I'm interested in the response. In theory, these guys have the tool knowledge and machinery to produce every part required to make a guitar amplifier OR a guitar. Additionally, machinists (even hobby machinists) are math-savvy.

Let's wait for a few days ... review responses from others and sort out the project - as a demographic excercise, interesting reading, whatever. (Not to mention that I'm tired and taking more prescription drugs than I'd like which slow me down.)

Randy

[randyc]

FWIW, Philip sent me a price list for transformers available in the U.K. If those prices are typical, it probably explains why there is less interest in "custom builds" in Europe. The cost of the two transformers in a fifty watt amplifier would exceed what we might pay for the complete amplifier !

Thanks for the information, Phillip.
RandyC

[goshawk]

Originally Posted by randyc

Let's wait for a few days ... review responses from others and sort out the project - as a demographic excercise, interesting reading, whatever. (Not to mention that I'm tired and taking more prescription drugs than I'd like which slow me down.)

Randy

Sounds like a plan.

[lpdeluxe]

Not much to add, just to assure everyone that I'm still hanging around (and waiting expectantly for the SH550!). Lots of stuff on my plate, and it seems that 99% of my playing is bass guitar these days, except for the odd date on Dobro or harmonica.

I now return you to your regularly scheduled programming.

[SamBooka]

I was hoping that with summer here I would be able to get on board but there is just too much stuff keeping me away. It sounds like a great exercise.

Best of luck all