Against “mechanical connection”

[Gaz]

Anyone who is studying up on tube amp construction (or even soldering) will hear the same phrases over and over: “the parts being soldered must make a solid mechanical connection,” and “solder is not glue!”

I took this advice to heart and made sure every wire was wrapped around every lug. Doing so took me longer to build anything and even longer to repair or mod. And more often than not I’d find a securely wrapped wire than hadn’t been soldered, but was causing issue under vibration. It was a problem I’d read about happening to others (and still come across all the time on forums).

The more pro amps I saw (vintage and new alike) inside of the more realized no one was following the rules stated above so religiously. Surprisingly none of their amps were falling apart with wire flying out of their places. I took a leap of faith, started simply sticking wires through pot and tube lugs, and just soldering them in place. When I learned about pcbs it became even clearer that this was acceptable practice (a flying lead can’t be wrapped around a solder pad!).

So I’m curious to hear other opinion about this subject and my rant. But I’m here to say that building and modding my own amps has never been more fun since I stopped obsessing about wrapping every wire, and now it’s much harder to miss a connection.

[Bloomfield]

I think a lot of that wrapping through lugs comes from back in the days of point-to-point and terminal strip construction in factories, where chassis would be assembled/ populated by one person and then passed on to another person to solder, so the parts needed to stay in place on their own. I do like to bend leads over after they go through lugs, and provide strain relief where possible,but the full wrap is probably unnecessary. It certainly makes disconnecting and moving parts a lot of work, as anyone who has stripped out an old point-to-point chassis can attest.

[Helmholtz]

The main reason for solder fatigue is mechanical forces (push, pull, vibrational) acting on the joint.

A solid mechanical connection makes sense where such forces are to be expected, as it relieves the solder from the mechanical forces.

With lugs in an amp, a simple wire hook is sufficient in most cases.

In critical cases it may be better to use stranded hookup wire, because it's less likely to exert forces on the joint than heavy solid wire.

[mhuss]

It's also good to put a bend in the leads of 'flying' components, e.g., from a board to a pot, so that the part is never pulling hard on the joint.

[mozz]

I was taught make the mechanical connection first. Now working on mil equipment and you would never pass inspection if you just pushed the wire through the hole and soldered.

There is a guy selling tube amps and stuff on eBay. If I told you his name or store you would say yes, I have heard of him. Well I fixed a pedal he built. It looked as if a second grade child put it together. Soldering was atrocious. I imagine his amps are slapped together too.

Maybe I'm OCD but I like perfect solder joints, done mil spec properly, for everything.

[Leo_Gnardo]

Anyone who is studying up on tube amp construction (or even soldering) will hear the same phrases over and over: “the parts being soldered must make a solid mechanical connection,” and “solder is not glue!"

In kits of yore, say 50-60-70 years ago, like Heath, Dyna, Eico, Knight and others, the instruction booklet often included a page or two about "how to solder" including these exact phrases. Partly to encourage the home-builder to be as thorough as possible when soldering, making it more likely to produce a functioning gadget, and make it less likely to have the builder query the company for advice or possibly send a poorly built kit back to have the company techs sort it out.

Yes a decent build can be accomplished without the full wrap-around milspec connections, witness Fender, Traynor, Marshall and countless others. Heck I've found factory built amps - even legendary McIntosh - where a line worker simply forgot to solder an otherwise "mechanically sound" connection and the amp worked for years. Not so much with say Fenders or Marshalls where the wire is stuck in an eyelet, with conduction between components, wires, tube etc left much more to chance, that is to say mere friction, should the factory worker not make a proper solder connection. Way on the overbuilt side, consider the insides of a PTP built confection, Matchless. So many bright shiny el perfecto connections on rows of tie strips, all those wires twisted and laid just so. Is that what makes them sound great (for those who think they do)? Sure looks good! For your own builds, mods and repairs as well, it does pay to give a bit of extra care.

One thing important to mention is the cleanliness of the surfaces to be soldered. Recently cleaned, bright metal is what we need here and a few seconds scrubbing with scotch-brite or wire brush or twirling the lead of your intended component lightly in the serrated jaws of a needle nose pliers can enable good solder connections. Neglecting this factor will leave you disappointed, also possibly wreck some of the components you're trying to solder.

[Helmholtz]

The reason why I ( and the instructions that came with my Dynakits in the 80s) recommend to hook the wire in the lug is that any movement of the wire during soldering might cause a "cold" joint.

There is no benefit from multiple wraps in amps.

[Enzo]

Well even if you wrap around, if you wiggle the part during solder it will be a cold joint.

There is motion and vibration, but heat is also a player. How many Fender HR DeVille or Deluxe amps have I had to resolder the power tube sockets? I always wrote that off to thermal expansion and contraction of the pins. WOuld that happen on a 12AX7 grid pin? Not likely, but other places it might.

[Pedro Vecino]

I have always thought that "solder is not glue!" It is aimed at those who neither know how to solder nor know how to glue

[Gaz]

I have always thought that "solder is not glue!" It is aimed at those who neither know how to solder nor know how to glue

Yeah, exactly. I think that's what I was getting at. That there's a point where beginner bromides are no longer useful, and knowing when to apply certain techniques becomes based on knowledge and experience. For example, you may want to wrap a OT primary wire around power tube socket lug for the high voltage and reason Enzo brought up. But you may just want to stick a straight wire through a low voltage pot lug for easier construction and serviceability. Thanks for all the thoughts.

[SoulFetish]

Yeah, exactly. I think that's what I was getting at. That there's a point where beginner bromides are no longer useful, and knowing when to apply certain techniques becomes based on knowledge and experience. For example, you may want to wrap a OT primary wire around power tube socket lug for the high voltage and reason Enzo brought up. But you may just want to stick a straight wire through a low voltage pot lug for easier construction and serviceability. Thanks for all the thoughts.

Unless you make a mistake on which is the correct phase orientation

[J M Fahey]

Beyond my very first amps, I never ever twist anything around anything any more (for some 50 years now) except the few cases where itīs convenient.

The caption is true: "solder is not glue" .... because itīs infinitely stronger **solder**

If *shotgun barrels* which are fired individually , canīt imagine any higher mechnical stress than shoulder breaking recoil, are *soldered* to each other , and we are talking lead-tin here, not brass or silver, then solder IS strong.

My reasoning is that IF a wire or component leg can move *at all* relative to a contact lug, solder is already cracked, so wire twisted offers no help ... too late for that.
And if solder is healthy, no movement means twisting is not doing any mechanical job.

If anything, tight twisting may help in a very poorly solder joint, either dirty parts or cold/cracked solder.
But the proper answer is to properly solder, of course.

[SoulFetish]

Here's another way of looking at this topic:

Many people reference NASA/s manuals on proper soldering technique, which has been used as a standard for decades, in which they often have strict mechanical requirements for their workmanship.

NASA THROUGH-HOLE SOLDERING TERMINALS

So, for NASA, it makes sense to have extra layers of redundancy because, in most cases, once their gear is operational, it is either impossible or extremely impractical for a technician to make repairs on some equipment.
I see the wisdom in it, however, as an amplifier tech, I think of Silvertone as an example where this makes replacing components much more challenging without breaking the terminal itself (ie tube socket pins.)

[pdf64]

Unless you make a mistake on which is the correct phase orientation

No need for that to ever happen; wire it up so that primary and secondary are in the same polarity. That works for everything apart from an AB165 Bassman.
With a sig gen and 2 channel scope it’s simple to verify.

[R.G.]

Then again, the devil makes me recount the tale where my amp-tech friend got in a 1960s Fender with a complaint of it making crackling noises. "It never did that before..." as you've all heard. When he opened it up and poked around to find the intermittent, poking on the wiring to the output tube sockets cause the crackling. He looked closer and found that the wires and components to the output tube sockets HAD NEVER BEEN SOLDERED. They were the original through-and-wrapped apparently from the factory. Lasted and worked reliably that way till after 2000.

Apparently, if your wrapping is good enough, solder is optional.