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Scratchy pots on Victoria Bassman

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9/8/2003 5:30 PM

Scratchy pots on Victoria Bassman

I have this Victoria Bassman here with scratchy volumes and tone controls,(and the scratchiness appears on the guitar volume pot too) Cleaning them is not the solution for there is DC all over the pots. My first idea is to start swapping out coupling caps, eventually replacing them all, yet the problem remains (I also replaced the 8uf filter cap for the preamp and the 250uf cathode bypass cap)....What else could be causing this??.Help!

9/8/2003 7:06 PM
Bukowski	UP

9/8/2003 11:42 PM
Randall Aiken	A bad preamp tube can draw too much grid current and cause a volt or so of DC on the controls, which will result in scratchiness. Try replacing the tubes first. Parasitic oscillations can also cause strange behavior. Randall Aiken

9/9/2003 6:13 AM
Enzo	Also check to see if any grounds have broken free. On eyelet board amps you will find for example several points where a number of componets are soldered togethre and a wire runs out to solder to chassis. In some other amps there are wires from these component groups to a grounding point. If one of those wires breaks, odd DC conditions can result.

9/10/2003 4:52 PM

Well, changing tubes was the first thing I did, to no avail. I've checked all ground points and the wires feeding them and nothing is out of the ordinary(I reflowed the joints just for good measure). There may be an oscillation though...It is a barely discernable whistling/crazy sound that starts when I poke my stick on the fiber board around the 68ks from the input. I can make it come and go, but the scratchiness remains either way....I've reflowed all the joints in this area also...

9/11/2003 6:36 PM

Sounds like you may need to do some serious troubleshooting. How much DC do you measure on the pots? Does the DC or scratchiness go away if you lift the coupling cap(s) that feed(s) the pot(s)? You could possibly have one or more leaky coupling caps or (shudder) a conductive eyelet board. If the coupling caps check good then I would pull the plate resistors up, just unsolder one lead so you can easily connect or disconnect them while monitoring the voltage on the offending pot.
If the board is conductive you may be able to clean it and dry it thoroughly before testing again. In a worst case you may need to replace a conductive board. If in doubt - find a qualified tech and have him check it out. There may be a simpler solution that is hard to see over the internet.

RE

9/11/2003 11:37 PM

There is about .250v to 2v on the bass and treble pot going up to the two volts as you rotate the bass pot up. The volume pots have around half a volt or so on them and they are the ones scratching the most. I replaced ALL the coupling caps as an act of frustration, with no change. I'm beginning to think this is the conductive eyelet board, it's the same material as an old Fender, not the hard shiny kind that you find in tweed kits and such. The bad news is I thought WAS a qualified tech til this beast came into my shop...

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