Hacker Mayflower 2. Hum.

[JohnSwift]

Hi just joined this forum.. I have just finished recapping and replacing resistors in my Mayflower 2 it sounds great, almost no hum with no treble cut, but as I turn down the treble (VR2) there is noticeable hum, even moving my hand near the control makes it worse... is this normal for these sets? Any advice appreciated

[Gabe001]

I don't own one but these have an excellent reputation. I would think there is something wrong with the pot - either the wiper has an issue, or the carbon track is damaged or there is an issue with grounding. This incudes grounding of the pot itself, not only the signal.

Have you done basic resistance measurements at the position the fault manifests?

[stevehertz]

I had the same issue and it turned out to be poor grounding of one or more of the many self tapping screws that are used as ground points on the chassis. Just tighten them all up and see if that helps.

[Goldieoldie]

I had this problem and it was to do with the screen cable to the pot.
Sorry can’t remember what the solution was ,possible earthing it to the chassis at both ends or just one end .

[JohnSwift]

Thanks everyone, will try these and let you know

[JohnSwift]

Originally Posted by Goldieoldie

I had this problem and it was to do with the screen cable to the pot.
Sorry can’t remember what the solution was ,possible earthing it to the chassis at both ends or just one end .

The cables to/from the tone control aren't screened... I found a thread about this. I will try replacing them. I even get the problem if I replace the pot with and r31 with a fixed resistor of the right value... feels like something to do with impedance... which I must admit I don't really understand

[stevehertz]

Originally Posted by JohnSwift

The cables to/from the tone control aren't screened... I found a thread about this. I will try replacing them. I even get the problem if I replace the pot with and r31 with a fixed resistor of the right value... feels like something to do with impedance... which I must admit I don't really understand

I'm not doubting that these cables can cause a hum problem, but it's strange that most sets don't suffer from the problem. Maybe the cables are dressed in a slightly different way?

[JohnSwift]

Hmmm, still planning to take a closer look. All options seem a bit unlikely but is has to be something I already tried tightening everything and my chassis is only painted on the outside... but it is interesting that it gets worse as the pot slider moves toward the 500pf capacitor to earth (yes I have checked the cap and taken the pot out of circuit, so it isn't the pot) which does make me wonder of it is an earthing problem... thanks again for the suggestions. Just to check... your Mayflowers don't hum when you turn the treble all the way down and put your hand near the tone pot on the back?

[JohnSwift]

OK, did everything, unscrewing, cleaning and re-earthing all the valve bases was a real pain, but did improve things a little. Then I replaced the unshielded tone pot vr2 with a modern metal pot and made sure the outside of the pot was in good contact with the chassis. That seems to have pretty much cured it.

Thanks everyone.

[Gabe001]

Good work. Glad it's sorted.