weird ARS capacitor

[Randall]

I have a Blues Deluxe in that was absolutely hacked to death, burnt off pads everywhere. I got it operating, but it still has a slight buzz and 3 Vac on the B+. I am reluctant to pull the board much more in fear of the ribbon cables I had to strip and reinstall (what a nightmare) being disturbed and causing further problems, so I am going to try to sell the idea that a small buzz is not worth the risk of flexing those ribbons any more than really necessary.

But I wonder about these two ARS electrolytics, they have the positive indentation on both ends like a nonpolarized cap, except they have the negative arrow pointing to one end as well. I have no experience with ARS axial caps, and have never seen a cap designated like this before. Anyone have any insight. The other axial filter caps are ARS as well, but with normal designations.



Also, the underside of the board is pretty burnt up where the cement resistors are, someone had done a crude job of replacing them and fixing the damaged traces. I wonder if the buzz may be stray voltages from the carbon, but as I said I think living with some buzz is the answer here.

[Mick Bailey]

3 Vac is about right for the first node. Check the ripple at the 1st preamp tube - it should be around 3 or 4mv.

[Enzo]

3vAC on the first node? That is less than 1% and sounds pretty good to me.

Is your hum 60Hz or 120Hz?

Have we tried to isolate the hum source? Hum is not generic. DO ANY of the controls affect the hum in ANY way?

Hum can easily come from unbalanced power stage, so make sure EVERY power tube has screen B+ present.

Also, Fender in this series was notorious for cracked solder on the octal sockets, so resolder all those pins.

[Randall]

Customer came for his amp this morning, but I can tell you the tubes are closely matched, sockets had all been re-soldered, and no control affected it. I didn't look into 60 vs. 120Hz, I suppose I should have. He is happy with how it now is, therefore so am I!

[nosaj]

Customer came for his amp this morning, but I can tell you the tubes are closely matched, sockets had all been re-soldered, and no control affected it. I didn't look into 60 vs. 120Hz, I suppose I should have. He is happy with how it now is, therefore so am I!

Doesnt 120hz hum signify a failed failing filter cap where the dc is not being filtered enough?

nosaj

[Enzo]

Not exactly. It tells us the hum is RELATED to the power supply ripple. Grounding could be the problem, if circuits share copper in the ground returns for filter caps. Caps themselves might be great, but there is a ripple charging current spike at 120Hz, and it can get into sensitive circuits.