Craig wrote:

Quick check through the random transistors I have reveals a BC182B NPN is available, I could use a little guidance on its suitability as a replacement for the rouge TR54 device BC173B....?

Craig

Go with the BC549B or 550B.

Ok rogue junction replaced and a test period (over 30mins) has established that the "rustling sound that is probably an easy fix" now seems to have been eliminated...............been a bit of a saga, but an enjoyable journey.....only the cosmetic side of things now.

following on from the success of the scope fault finding I have recovered the woodwork with some left over veneer, could have sanded the scratches and marks out of the original to be honest.....but wheres the fun in that. Sanded down and first application of shellac applied

Hi Craig.

Rustling / crackling sound from a bad transistor or diode junction may be localised using electronic freeze spray on each suspect component, without the extra work of swapping components from channel to channel.

Alternating freeze spray, waiting for change then with a little heat from a gas soldering iron or SMD rework station is usually sufficient to isolate a defective device. The rustling / crackling will change in intensity with temperature. This is a pretty standard faultfinding procedure for audio equipment.

HTH in future endeavours.

Colin.

Thats interesting....I have heard of this but have steered away from it as I know if you supercool something it passes a lot more current, I have always worried in case damage to the downstream components could occur?

Craig

Never had an issue with this method in 20+ years.. its a bit of a time saver. A drop or two of freeze is enough usually, but the important thing is to apply and wait.. it can take 10 to 20 seconds to cool the junction in the device through the case, and therefore to hear the change in the noisy part. Keep volume to a minimum and use a non beloved speaker for test, just in case you get any DC crackling.

Nowadays my favourite time saving tool in the arsenal is a high resolution thermal imaging camera, but that's another story.

The -40 degC of the cooling spray is far from supercool (-200 degC or lower).
It will not significantly affect any currentflow.
You can safely use it.

Martin

Thanks for that.........It's certainly something I will try the next time I have such a fault, swapping/replacing components is time consuming it's true.

Craig

Finally got around to finishing the case.........