Princeton Reverb revisited.

[Ron53]

Not been around for a while - moving house etc, so am returning to an amp build that always had a problem I was determined eventually to fix! I am a beginner basically, but have built quite a few Fender clones for enjoyment and for the achievement, remarkably successfully. This one always had a constant crackling noise that I could never pin down (I always suspected my not always perfect soldering). So, months later I have now sorted myself out a bench in the garage, some peace from the kids and the time to take a fresh look. So - chassis out - on a nice new chassis cradle courtesy of TAD (expensive but I wish I had bought one years ago). As soon as I switched on and the tubes started warming up there was a curl of smoke. Even I know that is not good. On further investigation this was coming from the 1K dropping resistor right at the beginning of the power train. This was a 3W metal oxide resistor - so not under valued (double checked also it was a 1K). This I assume had nothing to do with the crackling and is something that has appeared since the amp has been stored (It never did this before - the amp worked fine, apart from the crackling noise). Frankly I do not know where to look for what is causing it to burn up. The only things that spring to mind would be a failed rectifier tube/one of the 6v6s or perhaps a failure in the cap can. Any suggestions what to check and how to check would be gratefully received. If I have not described the resistor in question correctly it is the one bottom left on the layout 'in series' with an 18k resistor,

[Ron53]

OK sorted that one!
It was the rectifier tube. The plastic central pin on the tube was snapped off inside and I had somehow plugged it back in wrong without realising it. A real beginner mistake - Doh!
I have some repair washers that renew the central pin by slipping over the pins - tube seems fine - lucky I didn't blow a lot more I suspect.
Anyway...back to the crackling.
Just renewing my experience of it. It is crisp-bag crackling sound that gets louder when you turn up the volume.

[norburybrook]

if voltages and everything else are OK, my first port of call with things like this is chopsticking around to see if I can pin point noises and or make them worse /better.

A good set of known working tubes is also very helpful so make sure you have those installed first.


I'm still a beginner too compared to a lot of people here so this is a just a couple of things I would do .


M

[TUBEDUDE]

Since the volume control drops the noise level, check all before the volume control. Does the noise go away completely when the volume is all the way down? It sounds like a cold solder joint.. try reheating your joints in the preamp area. Don't forget the power string feeding those circuits. Carbon comp plate resistors will absorb moisture when stored so they need to cook for a while to chase out the water,, but you said it crackled when it was assembled, so I'm guessing a cold joint. Which Fender did you clone? It will be easier to troubleshoot with a schematic and photos.

P.S. I really enjoyed your video on Trainwrecks etc.