In older SS amplifiers, particularly Hi-Fi units, but also instrumental amps, they used to glue large components with some white-ish glue, very flexible, tacking like hell. Also, wires were glued to the PCB where the joined the PCB, for a strain relieve. It does not look like hot melt glue.
I could never find out what this was.
Sometimes you have to replace a worn-out cap. It is not easy to remove the glue, but it appears not so easy to find a comparable glue to secure it again too.
How do you guys do that?
Quote from: aquataur on April 17, 2026, 04:33:06 AMIn older SS amplifiers, particularly Hi-Fi units, but also instrumental amps, they used to glue large components with some white-ish glue, very flexible, tacking like hell. Also, wires were glued to the PCB where the joined the PCB, for a strain relieve. It does not look like hot melt glue.
I could never find out what this was.
Sometimes you have to replace a worn-out cap. It is not easy to remove the glue, but it appears not so easy to find a comparable glue to secure it again too.
How do you guys do that?
Honestly, I never add strain relief glue because I don't gig my gear or ship it to customers since it is just for me. If I were to add glue, I would probably use silicone - same stuff you use for sealing around bathtubs etc. It is normally good for up to 400F (verify on the tube you are buying), sets up fairly quickly, lasts practically forever, and is very strong.
Unsure what was used at the factory though - but I do know the stuff you are talking about and am curious myself if anyone happens to know.
I do add strain relief, even if I don't carry the gear around, because I permanently refine my gear, although for my purposes I have found better ways than glueing.
Last day I had to repair an amp, and many companies use this stiff ribbon cable. If you flex them often enough, they break. If you anticipate extensive problem locating sessions, then glueing may be a wise thing.
I have read some threads, and people indeed use silicon glue & sealant for that purpose, however, stock household silicon exudes acetic acid, which can become a problem soon. There is a "neutral curing" silicon, preferably exuding alcohols, that is used for electronics.
Silicons have the disadvantage of, once opened, curing in the dispenser quickly, so when you want to use it a few weeks later, its cured...
Agressive glue should positively be avoided.
I read that vintage amps from Sansui suffer from such a case.
Contemporary PCB makers suggest neutral silicon, because it exudes no "dangerous" compositions.
I have used SMP glues (sylyl modified polymers) that exsude alcohol (ethanol or methyl) upon curing.
The companies seemingly like to shroud their compositions in mystery, so we might meet anything like "silane-modified polymers, modified-silane polymers, MS polymers, silane-terminated polymers (STP), MS Hybrid, Hybrid, Polyoxypropylene, or "silane terminated polyether (STPE)" ::). These might work.
Exact product names are futile because every country has their own.
A sure sign is that the glue needs moisture to cure.
SMPs tack like hell and stay flexible.
I use electronics-safe silicone, which you can get from places like digikey although it is fairly expensive compared to regular silicone.
As you say, if you look around, you can find stuff that is neutral curing without the high price.
Some of the glues that have been used in the past have ended up breaking down over the years, and causing conductive paths that create various faults. In many cases they are too difficult to remove and the unit becomes a write-off.
Some are not even that old, there are fairly new Marshall products now showing up that have glue which becomes conductive when in contact with high voltage (in tube amps).
Sometimes I tend to believe that they are doing things deliberately, but in case of the Marshall glue, I believe even the most benevolent glue manufacturer would have a hard time to foresee the effect of high voltage.
That said, the number of glues available is exploding. The market pressure is probably enormous and long time evaluation is self-excluding.
I'll order some SMP glue and report back in 10 years.
Personally I use metal or plastic clamps or zip ties to secure components. I use a dab of silicone inside capacitor doghouse boxes in fender tube amps. When I open up some huge bass amp and I see glue boogers globbed everywhere I get fight or flight instinct. I really would like to see a zip tie carefully around the circuit board with holes to wrap and secure a huge cement wire wound resistor. Perhaps these zip ties held a heat sink device to also help dissipate heat. But that costs more money than the company would ever be willing to spend. So they at least try by squeezing a bunch boogers everywhere with little regard for any trouble it actually causes.
Quote from: DrGonz78 on April 22, 2026, 11:48:32 AMPersonally I use metal or plastic clamps or zip ties to secure components.
That's what I prefer with my own builds too. I remember BTW seeing large cement resistors being held with a soldered piece of copper wire (connected to nothing of course).
Quote from: DrGonz78 on April 22, 2026, 11:48:32 AMBut that costs more money than the company would ever be willing to spend.
Exactly. They are saving at all cost. How much more effort labor-wise and cost-wise would it be to make it properly?
But such a unit may last longer and be serviceable - beware of that.
Such an approach is reserved to the Military.