music, guitars & other obsessions

Designing Vacuum Tube Amplifiers And Related Topics by Charles Couch – A Book Review

The Book

I have been building guitar amps for about a year now, so far, the builds were nothing more than “paint by the numbers” exercises, i.e., simply follow existing, proven schematics, made mods as needed… Pretty straight forward really. Of course, I learned a lot already, for example, parts selection, construction and troubleshooting techniques, wire routing, grounding and shielding, chassis and component layout, front panel design, etc. Perhaps more things that are not really “electronic” per se. And there are many more things that I still yet to learn. In any case, now I am ready to move up to the next step in the amp building ladder… Building my own designs.

I have been on a quest to collect as many tube design software, worksheets, schematics and datasheets as possible. Well I think I have already too many… more than I can ever hope to digest, really! So for past week or so, I have been going through the various software and worksheets systematically to see if I can put some of them to good use. It is through this search that I came across Charles Couch’s great work. The title of the book is “Designing Vacuum Tube Amplifiers And Related Topics”, with the nifty tagline “Written for and about tool-capable guitarists who can use a pocket calculator”.

I downloaded Charles’ book and software quite awhile ago, I think I merely glanced through the content pages without even reading the book – well that turned out to be a mistake – had I done so, I would be much further along on my learning curve. Well it is never too late, I suppose.

Unlike the well-known authors like Merlin Blencowe and Morgan Jones (where are the American writers?), who put out quite a few good books on amp building and design in the past few years. Charles self-published his book online (available at Scribed), and I have never heard anyone online mentioning it. Even doing a search now turned up very little… Anyway, I think this is a great book and just what I was looking for.

The book is very well written, with many instructive examples along the way, it is not overly mathematical like many of the older text books on vacuum amplifiers and tubes but Charles does go through the math when they are needed, he is after all an experienced (retired) solid-stage design engineer. The book follows a logical sequence which I really appreciate, unlike some of the other books, which appear to leap from subject to subject – just a bit too much for my taste.

As a bonus, Charles Couch also created an accompanying Excel worksheet, so some real design work could be done with the knowledge gained after reading his book and following the lessons provided. I think the two combined are definitely the best package on the subject (for guitar amplifier design) that I have found so far. Rating: 5 out of 5!

Snapshot of the software

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6 responses

  1. Charles Couch

    Having seen it for the first time last night, I am very flattered by this review. Many thanks for reading my book – you are exactly the person(s) for which it was intended !

    Charles R. Couch

    January 20, 2013 at 1:05 pm

    • jazzbo8

      Charles, I have learned a lot from your book and the worksheet, so I am glad that I can thank you directly. I am just surprised that not more builders, wanna-be designers have seen this document, my review hopefully will allow more to discover this gem!

      Jaz

      January 22, 2013 at 8:19 am

    • john henderson

      hi ,i have modifying and repairing tube amps here and there for some time now ,being a first year design technician (left college 20 yrs ago),and needed less convoluted calculation sequences than i see in most tube HIFI diy-ers books ,i have been reading through youre ebook designing vacuum tube guitar amps,and decided to run a parrallel design using 6v6’s for an output of 15watt and RCA tube data sheets,for Imax X Eb=3.125 X 15watt = 46.875 and (Ec2=250Volts) Ib@Ec1=0V centre point looks like ~115.5mA so signal voltage Eb is 46.875/115.5mA=405.8V.Would the 46.875V be the saturation voltage to be added to 405.8V to acheive full linear(as poss) signal swing up to 452.675V 60% of this is 271.605V .Reffering to the worked example for the 6JN6 60% of 286V is 172V giving 370mA,For the 60% voltage figure of 271.605V i measure 116.5mA plate current its gone up?. i realise that V X I = P and a tube rated higher in plate current can generate reasonable power using less signal voltage ,i thought the signal level of 405.8V overly high ,as the 6v6 is a 14 watt device and need only generate 7.5Watt per tube for 15 watt in pp A-B mode.it seems as though plate current has Rissen at the 60% of Eb value.do these figures seem true,in summary up till this point ,for less out put power and for a tube that has a 4 watt max differrence from the 6JN6 it seems to have far greater sig swing and Ip goes up at 60% voltage.the calculator (casio fx82L)isnt faulty,the calculations were done in tandem,data sheets are measured with straight lines on a grid matrix so no two points can be confussed,i stopped at page 66 sec 8.5 as i just think something is wrong,confusingly enough,The Pout= 0.32 X Imax X Eb==0.32 X 115.5mA X 405.8V = 14.998368, close enough to 15Watt for anybody,would you check this for me please,as the rise in current of~1mA opposed to the 6JN6 example going down by 1mA for a 60% voltage level.i am going to continue to see what happens thankfully my gas oven is broken and my head wont fit.
      regards,john henderson.

      February 11, 2014 at 5:49 am

      • jazzbo8

        Hi John, Thanks for writing, in any case, I did not write the book, it was written by Charles Couch. Definitely one of the most informative (for free at that) I came across when trying to learn guitar amplifier design. In any case, I am on the road now, but give me a day or two and I will get back to you on your query.

        Cheers,
        Jaz

        February 12, 2014 at 2:32 pm

      • jazzbo8

        I tried to draw the load line using your 6V6 example, here’s what I came up with, is this what you had in mind?

        6V6 example

        February 17, 2014 at 7:56 pm

      • john henderson

        ill have to look for the calculated results i came up with,im replying to say thanks for taking the time ,ill check it out though.right now i have been working through some calculations from principles of power by kevin o’connor, for SE design for guitar amps,with no refference to load lines a string of calculations are given of which 5 strings are devised, 1/ SE 2/ pp class A 3/pp class A2 4/ pp class AB and 5/ pp class B.i cant understand how, when this would assume all tubes are the same in push pull the average Vsat is used for Vload pk,40v for6v6,el84 50v for 6l6,el34 and 90v for 6550,kt88, common enough tubes but ive just used the SE calculation on a 6l6 20Wpk,10Wrms output which gave a Vdc i take it to be Vq at57mA and Ipk=Vdc(Vq) X square root of 2= 81mA ,at 350 Va or Vq as grid voltage is bias voltage, negative grid Voltage is given as approx square root of Va= -18.7V.now if the Ipk is at 0Va/81mA point or on the load line ,either way the bias resting point for no signal of 57mA is sitting at around -36Vfor the 6l6 GE data sheets and curves for the 6L6-GC.this is double the calculated -Vb,i could go on with this,if you would like to peruse these calculation sets and ones for transformer based outputs as well ill post them for you ,id rather do it on a private email in case of copyright .ive yet to get a single tube in SE to coincide with anything built by fender as a champ output.to be diheartened would be an understatement,chin up and carry on i supose,regards jh.

        February 18, 2014 at 3:21 am

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