Wiring/Soldering Technique Question

[Omar]

Looking at the Komet pics had me thinking. When you mount a grid resistor on the tube pin, how do you solder the wire to the resistor?

Here are the ways I have tried:

1.) Make a loop on the resistor and solder the wire which has a "J" hook

2.) Keep both straight and solder them together

I usually do #1 but I don't like how it looks when I heat shrink it (I know it's a petty thing).

#2 looks better with the heat shrink

What do you do it?

Omar

[wrecked]

Hey Omar!

Here's the way I do it, ripped from MIL-HNBK-2000 Soldering handbook.



Just tacking it through the hole isn't really something I'd use on someone elses amp, but it's fine for trying something out in a pinch. The solder shouldn't have to provide any mechanical support for reliability's sake. What part of wrapping it doesn't seem to heat shrink as well? I can't really see much difference if you wrap it around the top part of the loop, but you could also try gently bending down the top half of the socket terminal to be parallel with the chassis.

Matt

[Omar]

Matt,
Actually I was referring to the other end of the resistor, where the wire and resistor meet, not the end that connects to the tube socket. Sorry if I wasn't clear.

I think the Mil-Spec thing to do would be to have a connector mounted to the chassis where the resistor and wire met but that's a bit of overkill, I think.

Omar

[wrecked]

Hey Omar!

My mistake, it became pretty obvious what you meant when I re-read the question

You're right on the money about the use of an insulated terminal for that job in most military equipment. I don't have any shots of these standoff terminals still in place any military gear (as they're one of the first things I harvest from them, since they're so hard to find new) but here's a photo of one type that are excellent for grid stoppers.



In the absence of a terminal, I think the keys to making the joint look nice when covered in heat shrink are to make an "eyelet" or J hook really close to the body of the resistor, use a minimal amount of solder in the joint and use a short application time and/or a heat-sink to prevent component damage from applying the iron so close to the resistor body. It's also really helpful to use a really small gauge wire for the center conductor of the coax. With unshielded wire, one little trick that might help in getting a more attractive final product would be to pre-shrink a layer or two of HS (probably of a smaller initial diameter) over the first 3/8" or so of insulation unstripped from the wire to build up the thickness to be about the same as the soldered joint. That way there aren't any wierd bulges and it appears more like the straight shot method.

Matt

[BWilliamson]

Now this is just my preference, but I don't like having resistors not supported on both sides if I can help it. It's overly anal retentive on my part as Marshall been doing it for many many years without problems.

Solution I came up with was to move the Screen Resistors to the board leaving the unused pin on the socket to anchor my grid resistor. In the pic you can seem them on the board next to the rectifier diodes.



One benefit of doing this IMHO, it streamlines the flow the power supply a bit. Komet's solution seems a little more elegant but I'm happy with my solution. BTW, this is an old pic and ran into a little bit of a hitch. The screen resistors get really hot, that was the first amp I used that type of resistor in they would scorch the board. Now using turrets to mount them to get them up in the air for better cooling and less board burning. The bigger sand resistors don't have the same problem but took up too much space for what I was trying to accomplish, plus the resistors I originally speced it out with are not longer available to me.

bw

[Omar]

It's overly anal retentive on my part as Marshall been doing it for many many years without problems.

Bill,
Yeah, this is totally about me trying to deal with my obsessive-compulsive behavior to wire an amp as neatly as possible! I'm so anal retentive that I drive myself crazy re-soldering stuff to make them look right.

The only problem I see with putting grid resistors on the board is that they are less effective than mounting them directly on the socket (see Aiken's Tech article on Grid Resistors).

Omar

[BWilliamson]

It's the screen resistors I mount on the board, not the grid resistors. It was a bad pic to use as it was taken in the middle of the process.

Here's a better picture of another amp, the screen resistors are mounted on the board in the same location. If you look at the power tube sockets you'll see the grid stoppers.



brentwilliamson

[Omar]

Brent,
Yeah, I knew you were showing the screen resistors, but I thought you might have been suggesting mounting the grid resistors to the board as well.

BTW, nice work on the amp!!! Is this the amp that was modelled after the Bogner XTC? I seem to recall someone building an XTC in a Bassman chassis.

Omar

[BWilliamson]

Is this the amp that was modelled after the Bogner XTC? I seem to recall someone building an XTC in a Bassman chassis.

Yep, that was me on Ampage awhile back talking about this. Was a fun amp to do and went together much much quicker than most of my builds.

bwilliamson

[Omar]

Well I have to give you props b/c you planted the seed for my Fatman amp.

The Bassman was a really good platform for a high gain amp.



Omar

[Dai H.]

Hey Omar!

My mistake, it became pretty obvious what you meant when I re-read the question

You're right on the money about the use of an insulated terminal for that job in most military equipment. I don't have any shots of these standoff terminals still in place any military gear (as they're one of the first things I harvest from them, since they're so hard to find new) but here's a photo of one type that are excellent for grid stoppers.



In the absence of a terminal, I think the keys to making the joint look nice when covered in heat shrink are to make an "eyelet" or J hook really close to the body of the resistor, use a minimal amount of solder in the joint and use a short application time and/or a heat-sink to prevent component damage from applying the iron so close to the resistor body. It's also really helpful to use a really small gauge wire for the center conductor of the coax. With unshielded wire, one little trick that might help in getting a more attractive final product would be to pre-shrink a layer or two of HS (probably of a smaller initial diameter) over the first 3/8" or so of insulation unstripped from the wire to build up the thickness to be about the same as the soldered joint. That way there aren't any wierd bulges and it appears more like the straight shot method.

Matt

There must be some company/ies who make terminals like that in N.America. I have some like that bought locally (Japan) from "Morimatsu" apparently. I could've sworn I've seen American terminals made of Teflon also. These are the ones I've got. They can be handy on tube socket lugs or on a Z-bracket, if you want to experiment but don't want to drill any extra holes in the chassis. There are some phenolic body (towards the top) and ceramic ("Steatite") ones (lower) :

http://www.morimatsu-group.co.jp/catalog/relay.htm#n02

[mhuss]

I just use a "mini turret board" as shown (using scraps from discarded boards).

--mark