Electrolytics and turret boards

[milocj]

I'm just starting a 5E3 build and I have a turret board instead of the usual eyelet boards. I've seen mention of electrolytic caps sometimes being microphonic if they vibrate and also seen newer PC board amps that have a dab of silicone around the filter caps. Should I put a touch of silicone down on the board before soldering my filter caps in place?

I've never done it on my BF or SF Fenders when I've done cap jobs, but I'm curious as to whether I should with the harder material that makes up the board for this build.

Thanks.

[Enzo]

While I suppose anything is possible, I have bever heard a microphonic electrloytic cap. The disc ceramic caps do get microphonic, and the occasional film cap, but those are not the electrolytics.

The reason caps - and other large components - are glued to the board using silicone or hot melt or something is not to prevent microphonics, it is to prevent them from vibrating enough to break free of their solder. Caps are large, and often the larger cement power resistors are. So those things get siliconed to the board.

The caps are a lot less likely to crack free from a turret board, but a dab of silicone under each one will make it secure. It has nothing to do with the hardness of the part board material.

The larger a part is, the more mass it has, and the farther the center of mass is from the board for the part. As things vibrate in the amp, those parts will exert greater mechanical energy against whatever holds them in place. In the case of a pc board, it is only the solder, and solder is weak mechanically. SO they glue them down.

Fender makes a number of model solid state combo amps where the chassis is a sort of wedge shape - taller in the rear than the front panel. When I see one of those come in the door, the first thing I think is loose filter caps. And then the customer opens his mouth and says "I has a loud hum..." and I know for sure I was right. In the center of the large main board will be two largish caps standing up, and one or both will be cracked free of its solder.

[petemoore]

Yupp tall heavy radials were not even pressed down to the board [that only helps a little], and had rocked back and forth enough to break the connections to the PCB, chopstick test revealed.
getting to the bottom of the pcb..
at any slow rate, the reflow repaired the connections, and then i put epoxy all around the bottoms of those barrels so the traces and leads could focus more on electrical connections than failing physical strength.
I did a similar thing to the input jack PCB, more looseness caused by pluggings into a loose jacks jacknut, a little epoxy stinking up the delicate areas that need connected but get yanked and pulled on goes a long long way toward reliability, the way some of this junk is made...makes me look good when i can fix it.
That said...I've seen really really old Fenders and other amps with axial filter caps across the boards which had no mechanical/physical connection problems.

[dai h.]

seems worse (i.e. more chance for breakage) the bigger the component and the more it's "hanging" (the more the leads from the lug/turret, etc. to the body of the part on both ends are long). A bit of RTV in spots is probably a good idea to help make things more roadworthy.

[milocj]

Thanks for the info. In my case I should be able to rest the Sprague Atoms on the board without worrying about them hanging from the turrets so I guess I should be okay.

[tubeswell]

In the 5F2A I just built , I used a nylon mounting bracket bolted to the chassis to mount a largish sprague atom filter cap upon, with a cable tie to secure the cap to the mounting bracket. Probably a bit old-fashioned I know, but easier to get in and out than hot-glued stuff, and just as (if not more) secure.