c1 c2 c3 c4 c5 caps ( KAT 6550 )

[mosschops]

Good Morning. with a lot of help from Richard and Bob i have got my amp running again all good. only one minor problem now which is slight humm from my speakers only when close to them.so .I think i will change c1 c2 c3 c4and c5 which type capacitor would be good I have had a look and there any hundreds to choose from
Regards Steve.

[TimN]

Are you sure it isn't a ground loop hum caused by a dodgy earth somewhere? If it stays the same level when you turn the volume up with no music then it probably is. Check the integrity of the earth in your amp (without it plugged in obvs.). Check your interconnects and RCA sockets etc. Try waggling and moving them around and see what happens.

Beyond that I think these may be a direct replacement for the original C1,2,3,4. https://www.cricklewoodelectronics.com/100H450.html

Or for a more boutique yet costly solution - although I needed to solder some connector legs (there is probably a proper term) onto them as they are supposed to be surface mount. https://www.hificollective.co.uk/cat...mlytic-hv.html

I used one of these for C5. Seems to work well. https://www.hificollective.co.uk/cat...-hv-axial.html

Other more knowledgeable folk may correct me.

Hope this helps. Tim

[mosschops]

Many thanks Tim I will have a look. the hum stays the same volume up or down but when i take out the interconnect from my pre amp (passive) it is very quiet
Regards Steve

[Richard]

Hi Steve, short the inputs of the amp RCA sockets and if the hum goes it's not likely to be the smoothing caps. Check the earthing arrangement of your passive and/or source connected to it. Is it a home built passive? If it's a metal case check if the RCA socket bodies are earthed across it or isolated etc. Some CD players and TT arms can be fickle in their earth arrangement.

[mosschops]

Good morning Many thanks Richard can i short the rca sockets with a interconnect cable. I will have a look after work. my pre amp is wood with metel front and back
Kind regards Steve.

[bob orbell]

Steve, I had this problem with mine a long time ago, did everything that members suggested to no avail, years later I was advised to lower the value of C5 from 120uF to 100 or lower ( I also read this somewhere. but cant' remember where ) I am sure I used 82uF and this removed the hum to almost nil. It is something to do with too much capacitance after the rectifiers, there is a limit of capacitance that the 5U4 will tolerate, it is in the data sheets. Bob

[Richard]

Originally Posted by mosschops

Good morning Many thanks Richard can i short the rca sockets with a interconnect cable. I will have a look after work. my pre amp is wood with metel front and back
Kind regards Steve.

Morning Steve, Yes plug an i/c cable in and hold a paper clip, coin, screwdriver blade etc across the pin and shell at the other end.
Check the passive pre with a meter set to low ohms/continuity. Check that the earth shells of the input and output RCAs are connected on all selections. Any case metalwork should also be earthed but multiple signal earth connections should be avoided. You may need to have a look inside but if it's a commercially made unit it should be ok.

[mosschops]

Many Thanks Richard and Tim i will have a look at the weekend and report
Regards Steve


































Richard and Tim thanks I will have a look at the weekend

[willslenco]

I've found that valves can also sometimes contribute to hum as they age?

[mosschops]

Many thanks all checked every thing and can find no faults sounds very good so will live with it . quick one can i use 450v for c5 as it seems to be360v on voltage taken from the test voltage in instructions.there are many more to choose from. I have fitted a complete new set of valves many thanks Malcom
Regards Steve