Do you have something to drain the caps and keep them locked down? Drained caps (electrolytic) have the nasty habit of climbing back up after draining.best have something that uses a power resistor and clips to drain in a controlled way then clips on to stop them climbing during the work.
Bleed resistors will allow the caps to do this automatically.
Bleed resistors will allow the caps to do this automatically.
What exactly would I need to do this? I doubt I have it currently, but I'm sure I can acquire it
If it was (sensible) me, I would draw out the circuit (schematic) first. This is a good learning experience in itself. The circuit could be posted here and "evaluated".
The "evaluated" circuit could then be (re)built on a full metal chassis, under the watchful eye of the forum.... Then you would be able to enjoy the DIY almost kit experience. Get a scope, a signal generator, a DVM and some kind of AC current limiting device / soft start, if you haven't already.
From a safety perspective I can never understand wooden chassis.
The "evaluated" circuit could then be (re)built on a full metal chassis, under the watchful eye of the forum.... Then you would be able to enjoy the DIY almost kit experience. Get a scope, a signal generator, a DVM and some kind of AC current limiting device / soft start, if you haven't already.
From a safety perspective I can never understand wooden chassis.
Indeed. I have a steel baking sheet here - a cheap way to have a top plate for prototyping with point-to-point.
I would strongly suggest that the OP would be better finding a local experienced engineer. Nothing stopping the learning by tracing out but cold corpses don't learn. Also it's better given they will learn faster and will be less likely to destroy or set fire to everything (house, pets etc). Once the noise issue is fixed, the experienced engineer can check the biases etc too.
Last edited:
On this - just to be very very clear - please don't spray anything near high voltage (even more so conductive/flammable solvents) until you know what the issue is and have guaranteed there's no voltage present.
Looking at the wring of this amplifier, someone has gone to a lot of effort to ensure there are no exposed wires, and that there is a proper star ground. Components look reasonably recent, so it cannot be constructed so long ago.
If it was mine, I think I would investigate getting a piece of 3mm aluminium plate cut to fit in place of the hardboard to plate, and another for the rear cover.
I have recently invested in some step drills, so not sure how straightforward they are to use, but if you had a set of them you can prepare a new top with an identical layout. [I have a set of panel hole cutters that leave a very professional looking hole, but there are a lot of different size holes that are potentially needed, and I never seem to have all the right sizes.] Then, doing one channel at a time, the circuit can be migrated to the new top plate, checking for suspect connections in the process.
At then end of this process you will have a much better idea how your amplifier is working, so if you still have noise issues, you will be able to differentiate between the different causes of noise, and be able to focus on the likely source.
So, a construction exercise as opposed to an electrical one!
If it was mine, I think I would investigate getting a piece of 3mm aluminium plate cut to fit in place of the hardboard to plate, and another for the rear cover.
I have recently invested in some step drills, so not sure how straightforward they are to use, but if you had a set of them you can prepare a new top with an identical layout. [I have a set of panel hole cutters that leave a very professional looking hole, but there are a lot of different size holes that are potentially needed, and I never seem to have all the right sizes.] Then, doing one channel at a time, the circuit can be migrated to the new top plate, checking for suspect connections in the process.
At then end of this process you will have a much better idea how your amplifier is working, so if you still have noise issues, you will be able to differentiate between the different causes of noise, and be able to focus on the likely source.
So, a construction exercise as opposed to an electrical one!
Last edited:
An interesting amp discussion. This includes an amp that I believe is very close to yours. Worth going through and tracing the schematic first then perhaps watching this: Valve Amplifier Study 024: The Williamson Push Pull KT66 Original 1947 Circuit - YouTube