• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

How to get started

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Hi all,

So many helped me me understand what I have in terms of parts to work from and what to do with them. That said now it's time for me to start getting to work on my guitar amp, but I am still very lost. last night I wiped the box down with IPA to clean it. but didn't want to touch any electronics because I didn't know where to start.

I will be using a Davis Model 106 Amplifier and frankly don't know where to begin.
a few questions I have:

1) Someone mentioned turning this into a marshal 18W amp. and that all I would need is a marshal pre amp. Can someone provide a link to a schematic? I think this is what I am looking to do and the more direction I can get the better. It seems like a fairly common conversion, but I have still not found a comprehensive walk though or complete schematic that I can understand.

2) I also understand that I need to replace a lot of components, what types of components need to go, do people take everything apart?

3) How should I test things (assume all I have is a multi meter), and what should I be testing?

4) Also since I will be doing a lot of soldering I need to buy a better soldering iron. I have a budget of about $100 and am looking for a suggestion of a good soldering iron for this kind of work. Do I need a vacuum function?

5) In order to make this look the way I am hoping it will I need to unsolder everything, but that seems like a disaster waiting to happen. It seems like the sockets for the tubes are riveted in place, how do people handle that?


If people would like any specific pictures of what I have just let me know where to photograph and I will. The same goes for components and other information. There is no schematic on, under or inside this amp unfortunately.

Also mods I apologize if this should go in the instrument amp section, but since many of these questions are about tube amps and general steps I figures I would start here.

Thanks
 
Could this be the schematic you are looking for? http://www.geckoamps.com/gecko001/davis106.gif
(Google is your friend)

Soldering Iron: I am a big Weller fan (google WES51 or WESD51), but you can probably find something comparable at a lower price. I would definitely buy one that allows you to regulate temperature. Even though you may not need that for this project, it's going to be a good feature to have for more delicate soldering "around the house".

Vacuum? Maybe, but a cheap desoldering gun from Radio Shack will do just fine for PCB unsoldering. If you do point-to-point, it's less relevant, IMHO.

I'll leave some questions for others to answer. :D
 
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2) I also understand that I need to replace a lot of components, what types of components need to go, do people take everything apart?

5) In order to make this look the way I am hoping it will I need to unsolder everything, but that seems like a disaster waiting to happen. It seems like the sockets for the tubes are riveted in place, how do people handle that?

2) It depends on the age and condition of the amp- usually you are looking at replacing a bunch of capacitors and probably some resistors as well. And, if you are converting to a 'modern' design, the input circuitry and tone controls will probably need changes as well.

I've done it both ways- replacing some parts, unsoldering parts from sockets, etc - and also just taking most of the amp out of the chassis (usually the rectifier tube socket can stay).
The second way-new sockets and components- is the way i do it now- faster and less hassle.

5) Sometimes drilling rivets can work, though often they just spin under the drill. At that point a sharp cold chisel can come into play. I usually use an angle grinder and just grind off the rivet heads from the top side. A straight punch of the correct size can then drive out the rivet.

As you imply, unsoldering components from old tube sockets can end with breaking off a lug (usually the last one). It is good practice, though.:D
 
2)
5) Sometimes drilling rivets can work, though often they just spin under the drill. At that point a sharp cold chisel can come into play. I usually use an angle grinder and just grind off the rivet heads from the top side. A straight punch of the correct size can then drive out the rivet.

If the rivet is in tight then gently drilling will remove the top of it.
If you press hard then the drill will bite and spin the rivet and might damage the pcb.
 
If the rivet is in tight then gently drilling will remove the top of it.
If you press hard then the drill will bite and spin the rivet and might damage the pcb.
Good points. Having 'the touch' counts for a lot- I don't have it for socket rivets.
You can always 'set' the rivet if it starts spinning, with a center punch or cold chisel corner into the edge.

By 'pcb', do you mean phenolic wafer tube socket material?
Most of those sockets that I've seen are so 'crispy' that I just junk them and put in a new socket. YMMV.

In the past, I've spent 15min cleaning up an old socket. A new one is a few dollars, so I don't do that very much any more!
 
I think so. When I Googled Davis 106 amplifier, I pulled up some links to rebuilding to one of the 18Watt 'Lite' variants.
So EL84 PP?

Yes I am reffering to an 18Watt Lite Marshall. The schematic posted seems to be what I have. I just have no idea what to do to transform this into a guitar amp.

I suppose my assumption was that there would be some step by step documentation of how to do this, but it seems I am coming up short. I don't think I have the knowledge (this is my first build), to figure this out on my own.

Here is the best info I have gotten thus far:

Gecko #1 - 18 Watt Lite III

I emailed the person who did this modification and he said he would try to send me more details. I was hoping to keep the chassis and box of the davis, so this seems like it might be a little more tinkering than I was hoping.

I guess I feel that I could easily swap some old components for new ones and then change some wiring or add a new circuit, but I don't have the details on what needs to be done and lack the knowledge and understanding to figure it out myself.

All of you help is very appreciated.
 
Carter: As mentioned the Weller WES or WESD51 irons are great choices. They have loads of tips available, and I would suggest Ebay or Craigslist for a good clean used one. Used they are easily less than $100. The only difference between the two is the "D" model has a digital readout, which you don't need. The non-readout model has a dial with temps on it, and is less $$. I have both, and use the basic one as my main iron, works great. The stock chisel tip will probably be what you want, or very close.

Pick up some 63/37 solder; it melts like butter and is easy to work with. IMO, it's easier to work with than 60/40. You can buy small quans of Cardas quad eutectic on ebay for less than $10.

Another good cheap investment is a set of clip leads for you meter. You can do hands-off live testing with these; much safer than probing a live amp with a hand held probe. Read the safety sticky here if you haven't done so already.

Finally, if there isn't one already installed, add a 220K-470K or so 2W bleeder resistor across at least one of the caps in the power supply. These will allow the voltage in the PS caps to quickly drain down when powered off.
 
I was hoping to keep the chassis and box of the davis, so this seems like it might be a little more tinkering than I was hoping.

I guess I feel that I could easily swap some old components for new ones and then change some wiring or add a new circuit, but I don't have the details on what needs to be done and lack the knowledge and understanding to figure it out myself.

All of you help is very appreciated.

You definitely have to do some learning before attacking your project - we all did/do. Perhaps this hobby is not where you want to spend your time? Every hour with the soldering iron is an hour less playing music, etc.

Also, you can pretty well forget about saving a lot of money (vs buying a tube guitar amp), since every new hobby has tool and parts (inventory) costs. Most experienced builders already have the tools and supplies they need and a well-equipped parts box, so the project cost seems low.

For me, it is easier to build a simple circuit 'from scratch' with new components and a bare chassis, than to modify an existing circuit for a new purpose.
 
Alright well I have had some bad news come up in the family recently so I don't think I will have the free time to even start this project, which is why I've been off this site/thread for a while.

Is there anyway I can use this Davis Model 106 to power a 2.0 system using a preout from a modern audio/video receiver? I am hoping that I can do this without modification, or just replacing a couple old caps?

Thanks
 
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