Wiring ground stars and other busy junctions

[Martin]

Hello
 I've been reading this forum for a while, and finally decided to join in.
 When I built my first amp, a Portaflex copy as per TUT3, I found that wherever I had more than 4 or 5 wires going to the same eyelet it got quite messy. Not surprisingly I ended up with some bad solder joints to track down. What I ended up doing was replacing the eyelets in question with machine screws mounted through the same holes in the eyelet board. I then soldered ring terminals onto the ends of the leads and bolted them together. It solved the problem and I used the same approach when I built my second amp.
 My question is what do you do when you want to connect a lot of things in one spot? I've never seen wires bolted to the board in anyone else's amps, but I've never seen eight wires trying to cram into one eyelet, either.

[makinrose]

Hello
 I've been reading this forum for a while, and finally decided to join in.
 When I built my first amp, a Portaflex copy as per TUT3, I found that wherever I had more than 4 or 5 wires going to the same eyelet it got quite messy. Not surprisingly I ended up with some bad solder joints to track down. What I ended up doing was replacing the eyelets in question with machine screws mounted through the same holes in the eyelet board. I then soldered ring terminals onto the ends of the leads and bolted them together. It solved the problem and I used the same approach when I built my second amp.
 My question is what do you do when you want to connect a lot of things in one spot? I've never seen wires bolted to the board in anyone else's amps, but I've never seen eight wires trying to cram into one eyelet, either.

I generally use larger eyelets for the ground connections or connections that have larger gauge wires attached.  Keystone make many sizes besides the standard 1/8" mounting hole size most builders use. Any of those size can be purchased from Mouser.   

Alternatively, you could use two or three eyelet of the standard size and connect them together.

[K O'Connor]

Hi Guys

Using the $33 eyelets (1/8" dia) and appropriate wire gauges for the circuit, there is usually no problem having quite a dense number of lead outs.

Most component leads are around 0.032" or so, maybe 0.047" for a filer cap lead, and the bus wire is usually #24 (solid-wire that is tinned). All of our kits and projects specify #22 hookup wire and shielded calbe is #22 or #24. I use #24 coax and 2-conductor shielded wire.

For some reason, a lot of hobbyists think that they need fat wire for high-voltage, and then buy #16 or larger wire. This is the wrong way around. High-voltage needs better insulation NOT a thicker conductor. Current in a tube circuits is a few milliamps or less, wgich is easily carried by very thin wire that is actually more difficult to work with and does not come with high-voltage insulation. There is a common very-thin wire that is solid-core and Teflon-insulated used for wire-wrapping - an old way to prototype and to construct low-voltage circuits.

TUT3 gives a list of wire gauges and their current capacities. These ratings are conservative and assume an insignificant temperature rise inside the wire caused by heating by that current. So, #22 is rated at 2A, which is high enough to feed the heater of an EL-34 or 6550 PROVIDED that is the only current being carried by this wire. TUT3 shows wiring solutions that allow all wiring in an amp to be small-gauge. You can find ratings charts where #22 can carry 90A - but this is with a temperature rise in the wire of nearly 100C !!! We do not want this in our builds.

The other thing to do is to tin the wire ends. I use stranded wire only, except for bus wire and links made from cutoff resistor leads. I twist the strands and tin it before making the connection to switch lugs, or for insertion into PCB pads or component solder lugs. The tinning should be "light" inasmuch as the solder should flow evenly over the wire and not obscure the individual strands. There should not be any "globs" or thick parts of excess solder. This tinning step helps keep each wire unitised and they will be easier to poke into an eyelet, especially if there are already many things there already.

Many hobbyists use hookup wire for the ground bus between eyelets. This is more expensive than using bus wire, and will fill the space more quickly since the insulation will occupy space above the eyelet and (maybe moire psychologically than practically) make the eyelet seem full before its time. However, hookup wire may be all you have and you just want to get the amp built. Digikey and Mouser offer bus wire in many sizes, both by thickness and length.

In the Portaflex project, there is no eyelet that has more than five wires. I can see that if you combined the three eyelets feeding the splitter ground that you would have quite a junction.

[Martin]

Thank you for your replies!
  I have bought all my eyelets from London Power and didn't know there were size options. I could also have distributed the connections among more eyelets, and will consider these things in the future.
  I use #22 hookup wire, and I tin the ends. I used hookup wire to connect the grounds, but I will consider buss wire in future.
With the Portaflex, I stayed pretty true to the schematic in TUT3, including the heater stand-off, the ground lift, the test jacks, decoupling, etc, but I confess I went my own way on the layout, although I incorporated the distributed capacitance concept. I can see where following Kevin's layout in the splitter area would have made for less crowded eyelets, although I will point out that from the input we see an eyelet with two shield connections, the grid leak, the cathode resistor, the filter cap, and the link to the next ground star, which is the kind of junction that for me was much neater after I bolted it together.
  What spurred me to start this thread was taking a look inside my second build recently, and thinking it looks like a dog's breakfast and if I was to do it over again, what would I do differently? For my second amp, I took the Ampeg preamp, added a tube with the triodes paralleled (on the principle that if you want more "tube" tone, use more tube stages), and mated it with the output section from the Kelly amp in TUT5. After some experimentation and tweaking I've ended up with an amp I really love, and use on most of my gigs. It's quiet, it's touch sensitive, it's the right power level for most of my gigs, it even looks pretty good on the outside, but when I look inside I want to start over again! The bolted together grounds aren't the worst looking thing about it, but it's a solution I haven't seen elsewhere and I half expected you to explain to me why I shouldn't do it that way.

 Despite my dissatisfaction with some aspects of my work, which is entirely down to me trying to do things my own way, I have two amps that I'm getting a lot of use and enjoyment out of, so thank you, Kevin, for all the guidance you have provided through your books!
 Martin