Old brittle insulation on circuitry is vibrating/buzzing. Easy solutions?

[pdf64]

Re the amp innerds photos, there's a high likelihood that the original cathode bypass ecap is non-functional, and a fair chance that the bumblebee cap is leaking dc.

[Triocd]

Great idea Tom, I didn’t think of bending them a bit. That should be easy to do and I think it’ll work. As a backup in case it doesn’t work, could there be any issues with getting a little superglue under tubing? I definitely could get superglue in there.

[Triocd]

Re the amp innerds photos, there's a high likelihood that the original cathode bypass ecap is non-functional, and a fair chance that the bumblebee cap is leaking dc.

Is the cathode bypass cap the brown “east Newark New Jersey” cap?

[Tom Phillips]

Great idea Tom, I didn’t think of bending them a bit. That should be easy to do and I think it’ll work. As a backup in case it doesn’t work, could there be any issues with getting a little superglue under tubing? I definitely could get superglue in there.

There is no electronic issue with using superglue. Just a possible inconvenience for future repairs. You can thank Enzo (post #13) for the bending idea.

[pdf64]

There's a brown one on the power tube and a white one on the preamp.
Any polarised cap (ie with + and - terminals marked) will be electrolytic; they are a consumable, limited life expectancy, just a few thousand hours at max voltage and temperature, plus they degrade if unused.
Hence it may be useful maintenance to replace them every couple of decades.
Ensure replacements are correctly orientated when fitting.

It's also a good idea to check resistor values, to ensure they haven't drifted too much; I've found 100k plate resistors that measure ~1M.
I think that most any in that amp can be measured in circuit, having ensured that the amp is isolated from the mains and de-energised first.

[Mick Bailey]

I use Loctite 410 'Black Tak' adhesive to secure loose/rattling insulation in old amps.

[Triocd]

There is no electronic issue with using superglue. Just a possible inconvenience for future repairs. You can thank Enzo (post #13) for the bending idea.

So I ended up using a drop of superglue on the 4 offending spaghetti pieces that vibrated. Worked perfectly!

I now have one vibration remaining which goes away when I put a tiny bit of pressure on the resistor to the right of the colored pencil in the 2nd to last photo. I can’t identify where in particular the vibration comes from. Possibly somewhere in the tube socket? I’m pretty sure it isn’t the actual 5y3 tube. Anyone have any ideas what could be rattling in or near a tube socket?

[Chuck H]

Actually, rectifier tubes can rattle mechanically. So can tube pin sleeves in the socket. If there's play in the resistor it's probably because of loose tube pin sleeves. Not sure how I'd manage that. Maybe Enzo's bend it trick on the resistor ends.

[Triocd]

There's a brown one on the power tube and a white one on the preamp.
Any polarised cap (ie with + and - terminals marked) will be electrolytic; they are a consumable, limited life expectancy, just a few thousand hours at max voltage and temperature, plus they degrade if unused.
Hence it may be useful maintenance to replace them every couple of decades.
Ensure replacements are correctly orientated when fitting.

It's also a good idea to check resistor values, to ensure they haven't drifted too much; I've found 100k plate resistors that measure ~1M.
I think that most any in that amp can be measured in circuit, having ensured that the amp is isolated from the mains and de-energised first.

Thanks, I do plan to replace anything old and out of spec in the near future. I’m familiar with discharging capacitors but can you explain isolating the amp from the mains?

[eschertron]

Thanks, I do plan to replace anything old and out of spec in the near future. I’m familiar with discharging capacitors but can you explain isolating the amp from the mains?

He's referring to simply unplugging the power cord to give (mumble-mumble)kV of protection from line source. Followed by discharging the caps, the amp becomes relatively safe to work on.

[Triocd]

Actually, rectifier tubes can rattle mechanically. So can tube pin sleeves in the socket. If there's play in the resistor it's probably because of loose tube pin sleeves. Not sure how I'd manage that. Maybe Enzo's bend it trick on the resistor ends.

Thanks for the info. Looks like it was a mechanical rattle in the 5y3. I replaced itwhi h solved that problem, now (sigh) there’s one more buzz that appears to be either the grill cloth or where the grill cloth is pinched against the cabinet. I had another Gibson amp in the past that had horrible buzzing all over the grill cloth that drove me nuts. I couldn’t find a solution and wasn’t in love with the amp enough to make a new baffle or recloth the baffle. The cloth on these old Gibson amps is as tight as a drum head and it seems vibration from the speaker can make the cloth vibrate. I’ll tinker with it a little to see if I can quiet it down, but I’m not too worried because I plan to build a brand new hardwood dovetailed cabinet for this since the original cabinet was painted an ugly yellow color and then someone attempted sanding the yellow paint off.

I also started planning to replace the caps and other bits inside today. A previous owner replaced the original can capacitor but instead of using 20/10/10 values they used 15/15/15. Any value in replacing these with the stock values? Is 15/15/15 close enough?

[Chuck H]

IMHO 20uf for a main filter is really tiny (HUMMMMMMMMMMMMM). I usually use 47uf there. It'll work fine with the 5y3 at typical Gibson voltages, I promise. Even a replacement can could be old, though maybe still doing it's job. I'd probably parallel a 22uf or 33uf @ 450V with the 15uf acting as the main filter and if the amp isn't humming I'd leave it at that. If the amp acts funny with oscillation or hum I'd just replace the can.

re: Grill cloth rattle... I know, right!?! If it's removable that would be an easy way to isolate if that's the problem. If it is, I've had luck jamming fat twine down between the frame and the cloth to give some space between them where possible.

[Triocd]

Right, I now remember when I recapped my Kalamazoo model 1 I went up to higher values for quieter operation and I’m happy with the results. What’s in there right now isn’t a can, it’s 3 individual capacitors. I might up the values but honestly I’m pretty happy with how the amp sounds. It has very little hum.

I’m happy to hear someone else has had grill cloth issues. Well, not really happy for you to have had to deal with it too, but honestly some people I spoke to before thought I was crazy when i mentioned it when I had that other Gibson amp. I find 2 vibration places on these Gibson grills...where the cloth meets the cab frame (where your twine worked) and where the cloth wraps over the very front edges of the actual baffle. I found both were really difficult to silence. I’ll try the twine though, thanks for the tip!

[Chuck H]

Depending on the color of the baffle, you can color the twine (or folded cloth strip or small backer rod, etc..) with a Sharpie marker so it doesn't show

[Triocd]

I'm going to be ordering some replacement parts today but I have a couple questions:

Does anyone know of a good replacement for a "bumble bee" capacitor? I'm not sure what the correct voltage is for these.

Also, does anyone know where I can get a grommet to securely seat the new 3prong cable through the chassis? I looked around a bit but I'm having trouble finding these.

Thanks!