I need a new bass pot for a vox cambridge V9310?

robgilmo

Its an Alpha A50K PCB mount, PIC HERE, The VOX Showroom - Vox Cambridge 30 Amplifier - A Look Under the Hood  Any ideas where I can get one and what type I need?

robgilmo

Im thinking this?

RV16AF-20-15K-A50K-3LA Alpha (Taiwan) | Mouser United Kingdom

robgilmo

I noticed they are sealed type pots? Sealed in that its hard to get cleaning fluid into them, I managed by totally soaking them and the few scratchy pots cleared up, would it be prudent just to replace them all?

Also, is anyone familiar with the issues regarding the opto coupler? Causing the amp to underpower when it fails due to its natural state being 'on'?

I went inside to take a look, mine is different, the opto coupler is four legged and has its own PCB running on fly leads, it looks factory, could this be a VOX factory repair under warranty or did they actually change it during production?
The problem being if this fails I have no idea what to replace it with?

ICBM

You really need to take the old pot out and do a careful visual comparison with the potential replacement - there are a lot of variations in bushing and shaft length which can make a proper fit to the panel and knob awkward.

If you can post a pic I may have a matching one, although it will be second hand. I keep all old pots that aren’t knackered exactly for that reason…

I do remember the opto-coupler being an issue with these too. That looks like a factory bodge when they needed to change the component type and the replacement wouldn’t fit the original PCB footprint, to me.

robgilmo

ICBM said:

You really need to take the old pot out and do a careful visual comparison with the potential replacement - there are a lot of variations in bushing and shaft length which can make a proper fit to the panel and knob awkward.

If you can post a pic I may have a matching one, although it will be second hand. I keep all old pots that aren’t knackered exactly for that reason…

Thankyou, I will strip it out when I do the tolex ,Its back together now. The black plastic bit that rotates inside the pot had broken in half causing the shaft to turn inside it. I superglued it, not ideal but its working for now. It will need changing though. There are people out there selling post specifically for this amp but they are silly money for a pot, 20 odd quid posted from Spain!

The reason I pulled it apart was partly because of the broken pot but also its losing power. It is sitting quite happily humming away but every once in a while it dies, no hum, no sound. To bring it back I have to strum the guitar quite hard and the amp crunches then comes back to life, it helps if I up the volume, it happens on both channels.
My first thought was dirty pot as some of them crackled or a dirty gain or mid boost switch as they crackled also. Cleaning the switches and pots cured the crackling but not the fault. If it is a switch issue its the trem or reverb as these work on both channels.

Next thing I will look at is input/output jack sockets, these are sealed so I cant get inside but I can get some cleaner into them.

The other thing I am thinking is speaker connections. When the faulty does appear there is nothing from the speaker, and only a spike in input brings it back, in my very limited experience I think this is a connection issue?

ICBM

Yes, that sounds like a bad connection which needs a voltage spike to jump across it. Check the headphone jack first.

If it's not that, the bad news is that it could be almost anywhere in the power stage, if it goes completely silent.

robgilmo

ICBM said:

Yes, that sounds like a bad connection which needs a voltage spike to jump across it. Check the headphone jack first.

If it's not that, the bad news is that it could be almost anywhere in the power stage, if it goes completely silent.

Good news, I spent the evening drinking a few beers and listening to Skynyrd demo tracks. I also let the amp run until it cut out, I then grabbed a 6-3.5 headphone jack reducer type plug thing and inserted it into the headphone jack a few times, it cleared it up, so I gave it a dose of switch cleaner and a few more insertions and its been good since, amp is working and sounding lovely,  thanks man, your advice is always greatly appreciated. 

ICBM

Headphone jacks on guitar amps are the work of Satan.