My FIRST Amp Build

[Whays]

Hi everyone, I'm pretty much a newb to the forums but have been around the site extensively for the past many weeks, it is good to be onboard.  As the subject line would imply, I am about to embark on my first amp build project. 

My target is the Fender AA864 in a head configuration.  My intention is to leave the NORMAL channel pretty much as is and run it the way the original was run.  Additionally, I want to take the bass channel, reconfigure it to a copy of the NORMAL and add a mids pot.  I may also do some other things in the tone stack but have not decided yet for sure.  For the record, I'm a country and blues guy, so big distortion is not my desired destination.

As this process unfolds, I'd like to ask the forum for occassional opinions as I go and perhaps I might be saved a "crash and burn" or two.

It is good to be among so much knowledge.

Wayne

[bnwitt]

Welcome aboard Wayne.  You came to the right place.  You're in for two treats. 
1. Gaining knowledge from the tubies in here
2. Plugging into your finished amp and hearing great tone. 

The 2nd one will hook you on building for life.  I'll help you when I can.

Barry

[Willabe]

Do you have a light bulb limiter?

It's a must have/must use tool for amp builders/repair guys. It can save the PT (and other parts) at start up if there are shorts.

It's easy to use and easy to build for little $$.

 http://home.comcast.net/~seluckey/amps/misc/Amp_Scrapbook.pdf


                            Brad      

[John]

Agree with the limiter. One of the few things I did right on my first build was build one, then use it after each segment of the build, for instance installed the PT and filter caps, checked it, hooked up heater wires, checked it, etc.

Shockingly, I didn't have anything shorted out. 

[shortfuse]

I on the other hand found out about the lamp limiter after I wired all my pre amp tubes backwards in my 1st build and had to buy a 2nd PT.  I now have one and it has saved me 2 times since I built it.  You picked a great forum to ask questions everyone on here is very helpful.

[Ed_Chambley]

Welcome.  Glad to have you.  So you are going for a real blackface bassman.  I attached an article I referenced when I converted a bassman head.  Has some good info.

+1 on the bulb limiter.  I made one just using a single metal box I had around the house with 2 plug sockets.  Had a light bulb adapter that screws onto a bulb and plugs in.  Plug the amp into the other socket.  Had all the stuff so why not.

[Whays]

Thanks guys for the welcome and the comments.  Not only do I take constructive criticism well, I also take advice.  That said, you can bet I will build that limiter.  Thanks too for the article Ed.  It is one that I already have a copy on file.  I've done a great deal of research getting to this point in time.  I'm still aware there is much I have possibly missed.

My first steps are to begin buying components.  I've got the chassis so far.  Next I'll probably get the transformers.  I'm thinking I'll go with Hammond upgrade models.  Then the passive components, resistors and caps, then pots and sockets.  Any words of wisdom or warning?

Thanks again,
Wayne

[sluckey]

Don't trim the OT primary plate leads until you are absolutely sure they are connected to the right tubes.

[Whays]

Thanks for the advice Steve, I will cetainly keep it in mind when I get to that point.  Hopefully, I will avoid some of those mistakes by the activities I've already completed.  As a Mech Engineer veteran of 30+ years, I do have certain skills that permit me to do precise detail layouts before cutting anything.  This may be a little dangerous to my ego, but I've attached a PDF of the layout.

Please share your thoughts.  Be open, I only have one feeling and it is pretty hard to hurt.

Wayne
http://www.el34world.com/Forum/index.php?action=media;sa=media;in=220;dl

[Whays]

I forgot to mention, this is a full scale layout, so I could make sure that everything would fit.

[tubeswell]

My first steps are to begin buying components.  I've got the chassis so far.  Next I'll probably get the transformers.  I'm thinking I'll go with Hammond upgrade models.  Then the passive components, resistors and caps, then pots and sockets.  Any words of wisdom or warning?

The PT will want a heater (6.3VAC) winding rated at least 3.3A (preferably 4 or 5A), and a HT (305-0-305VAC) winding rated at about 200mA for an ample supply (although 150mA will 'work' okay for guitar). If you forget about the bias tap when you've ordered it, you can always make a bias supply off one side of the HT winding.

The OT will be around 4k Pr Z. If you get an OT with 4R, 8R, and 16R secondary taps, you can use just about any (appropriately power-rated) guitar or bass guitar speaker (or combination thereof) that you can find.

The choke can be one of those 90mA DC-rated chokes (or even 50mA rating will be fine) - anything between 3H and 10H will be fine.

[Whays]

I really would appreciate any comments on my chassis and board layout.

I uploaded a copy, see the link above.

Thanks,
Wayne

[Danskman]

Nice layout! If you get hum at the end, you could separate the preamp filter cap ground from the PI and power amp filter caps ground; just connect it near the input jacks ground.
Speaking of trannies, Doug sells very good ones, built like tanks and reasonably priced.
I look forward to see pics of your finished Bassman; I build an AB165 and it's a very nice voiced amp, one of my preferred in the long list of Fender amps.
BR,
Danskman

[Whays]

Danskman, thanks for the words of wisdom, I will that thought for sure.  I will probably go ahead and seperate them as you suggested.  It's certainly not hard to do at this point.

It is appreciated.
Wayne

[HotBluePlates]

... As a Mech Engineer veteran of 30+ years ...

Oh god, a mech is gonna mess with wiring!!  Just kidding; I was briefly in school for electrical engineering, and I can't say I did great with the introductory stuff for mechanical or civil engineering.

I'll need to digest your layout a little, as circuit elements are faster to spot in a schematic.

However, one question does come to mind: are you planning to use a sloped-front chassis like the Fender original? If so, you'll want to model the physical size of those filter caps arranged near the front panel, as well as the size/depth of the pots. If you use Sprague Atoms, they likely won't fit. Then again, you don't gain anything by using Atoms instead of more modern, and smaller, axial caps like Nichicon. Most modern caps will be small enough to fit easily.

Since your two channels will be similar outside of the mid control, you may want to change tone stack values. Right now, you have 250pF/0.047uF/0.1uF for both channels. I'd highly recommend changing one channel to 250pF/0.022uF/0.022uF to give an alternate sound. I have tried this setup before, and it gives a similar but less-muddy bass. The treble cap (250pF) could probably be swapped to another value as well, but you'd want to breadboard that and see what gives you the sound as response you like. Or you could taste test in the completed amp.

I gather from your first post you want largely clean sounds. What guitars do you use most often, and what recording most captures the sound you're after?

[Whays]

First, thanks so much for the comments and suggestions.  Yes, to your first question, I do intend to use the sloped front chassis as was the original.  I do see what you mean by it not fitting due to the front slope and the pots.  The size you see on those caps are the Atoms.  I have also identified an Illinois Capacitor that comes in a 25% smaller package if room becomes scarce.  I can also shift the board slightly to the rear to make more room too.  Once I get the pots, I’ll create a 3D model before drilling my chassis.  I can always slip the filter caps into a can on the bottom of the chassis if I have to, but hopefully not.  A big thank you for the “heads up”.

I like the different tone stack idea on the other channel.  There is no reason not to experiment a little in that area.  Creating a breadboard, sounds like the way to go.

You are accurate in your assumption that I am after more of a clean tone.  My first love musically is country and I have admired a great number of pickers, both past and present.  I do also enjoy Southern Rock (i.e Lynyrd Skynyrd and similar) as well as several varieties of the Blues.  I have two 96 American Std Teles that I play the most as well as a 2000 American Std Strat that also finds a little play time.  Signal path?  I don’t even own a distortion pedal, never have.  My signal path is quite clean, with the amp providing most of the interest.  I do add a little flavor upon occasion but not much when I do.

An ME with electronics?  I may not be the sharpest knife in the drawer, but I am very careful and I go to great lengths not to let the magic blue smoke get out.  This is not my first pass at building electronic things, but it is my first amp.

Thanks again!

[Whays]

So far, I've only done a 2D layout and it has been uploaded (see above for the  link).  I will be glad to also upload any 3D that I might do.

Wayne

[SILVERGUN]

Hey Whays, you must check this out...
It's basically amp porn, but really lets you see all of the different approaches:

http://www.thegearpage.net/board/showthread.php?t=334977

[Whays]

Wow, that is some cool looking handy work.

Thanks.

[SILVERGUN]

Yeah....I'm working on a couple designs and this thread really helped. Just in case you didn't notice, there are 70 pages to that thread!!!....it just keeps going and going...

And don't miss this:
http://www.el34world.com/Forum/index.php?topic=3273.0

There's a ton of info. right on that page alone

Good luck with your build, and please keep us updated

[Whays]

OMG!  There is just a butt-load of info there.  It looks like I could spend forever in there and never get through it all.  Thanks for the tip.