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  • How To Build A Tube Amp, or Burn down A house.. Phase 1 the Research.

Awesome, looking forward to watching this build. Out of interest, where are planning to get your reverb tank?

So I put in the master volume And a switchable attenuator.

Attenuator has 3 levels, -3, -6 and -10. I didn't use his exact design but it's the same idea... And honestly I'm underwhelmed, even -10 is a surprisingly small reduction and I never use the other two.

Master volume on the other hand gives you a massive range and I seldom turn it up above half way, even at the garage days jams. Almost all of the clips I've posted on the group have the master set to less than 20% with kids sleeping in the next room.

That said, the 10% attenuator is an easy mod and does give an extra option if you want to drive those output tubes a little harder. Just remember that those 25W resistors need a heat sink (chassis works well), I completely missed that at first.

Yeti Awesome, looking forward to watching this build. Out of interest, where are planning to get your reverb tank?

from Tonetube.co.za
as well as all the Valves and Valve sockets.

and my speaker from Musicmadness

That is so far what I've sourced..

also going to need to do the Pedal for it, which should be fairly simple from what i understand, basically just 2 switches.

    While I was working on my amp last night I remembered this excellent article on grounding and thought you might be interested. Unfortunately I don't have a link for it and don't even know where it is from because I'd love to read the rest of the book. I followed it's advice and used a star grounding scheme and I'm pretty sure that it is a major reason that my amp is nice and quiet... or at least was before my mod... holding thumbs it remains that way.

    https://www.dropbox.com/s/0jee3ba0nbwinlh/Grounding.pdf?dl=0

    Thanks
    will definitely give it a read.

    since we are sharing, here are a few i have collected.
    Amps

    5 days later

    So today my books arrived..

    so the one is as I predicted, just a book filled with marshall amp schematics..
    the other.. Build a tube amp... I thought was HOW to Build a tube amp.. so another book filled with schematics.. :facepalm

      Yeti
      thanks will definetly keep that in mind..
      pity its 22ga.. My Bom Calls For 18ga and 20ga so will try my hand at google foo

      ?

        Tuckstir Fair enough, let me know what you find.
        I'm only planning on using this right at the very front end of the amp where there is almost no current so 22ga should be ample for my needs.

            RobbieZ

            Thanks RobbieZ , I have added the 2 books to the Google drive folder above, also have a few others if you want to browse

                Yeti Unfortunately I don't have a link for it and don't even know where it is from because I'd love to read the rest of the book.

                I’ve found it! Turns out it’s one of the sites I linked to in an earlier post (although that isn’t where I got it). Trying to get hold of the book but it doesn’t seem to be available as an ebook.
                http://www.valvewizard.co.uk/Book1.html

                  Yeti

                  Thanks , will try to source one digital copy. but looks like a difficult Google-foo battle from what I Tried this morning

                  In the meantime I see Takelot has a copy for sale..which I might just get next month..

                  • Yeti replied to this.

                      Tuckstir Thanks for the link, I hadn't tried that.
                      My google foo failed spectacularly. Just pages and pages of SEO sites with no real content. I did find one on scribd but I cancelled my subscription a few months ago. Incidentally, I contacted the author directly and he confirmed that there isn't an official electronic version. He did send me this link however and told me that I'd find most of it there.
                      https://www.google.com/search?tbm=bks&q=merlin+blencowe

                        Hi, Tedibear. I have a full 18W Plexi schematic and a copy of the book Electronics for Guitarists, which has a chapter on tube power amp design, if you are interested.

                        How can I add the documents to your Google Drive Amps folder?

                        Johnny-B
                        You should be able to drag and drop.. check, I have just edited the permissions so that shouldn't be an issue anymore if it was.

                            A question for the more electrical minded folks.
                            on the 2 Princeton schematics I posted above i noticed the bias's are different.
                            Princeton AA1164 uses a self-correcting Bias
                            vs
                            Hoffoman Princeton which uses a fixed bias.

                            From what I understand the fixed bias is trickier to set up correctly as it calls for a good ear, some hardware I don't own and something down right dangerous..
                            so why would I good for a fixed over a self-correcting bias, are their any real/perceived advantages of one over the other?

                              I'm far from an expert and have only really done fixed bias myself... so again, pinch of salt.
                              What I understand is that fixed bias gives you more control.
                              1) You can vary the bias by twiddling a pot rather than swapping out resistors (although I suppose there is nothing stopping you from using a variable resistor in cathode bias).
                              2) As the bias is set externally it does not vary with loading like a cathode bias does so it keeps things more consistent (good or bad depending on what you're looking for).

                              From http://www.valvewizard.co.uk/pp.html
                              "Cathode bias often lends a natural compression or 'squishiness' to the sound, due to the increase in bias voltage when one valve enters Class B conditions, though the larger the bypass capacitor, the less will be this effect. A small capacitor (less than 100uF say) also increases non-linear distortion, which may be significant in hifi. Using a very large capacitor (greater than 470uF say), or using no capacitor at all, reduces this effect.
                              Fixed bias on the other hand, remains the same at all times. This allows maximum output power to be developed, and the reduced compression gives faithful transient response, or a stiff or 'barking' overdriven sound.
                              Furthermore, there is no reason why we cannot use a little fixed bias and cathode bias simultaneously to achieve the desired mix of compression and 'bark'. "

                              If you're interested, this is the method I used to generate my bias voltage... and to be honest, I just set it to the nominal value from the schematic and left it there. It sounds pretty sweet so I haven't been inclined to fiddle.
                              https://robrobinette.com/Generic_Tube_Amp_Mods.htm#High_Voltage_Tap_Adjustable_Bias

                              Out of interest, one nice side effect of using cathode bias is that you can use VVR to do power scaling and get some really good tones at low volume.

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