KEL84: Humming, growling, screeching and screaming

[Sid and Coke]

Hello folks,

Just had a weird one with my KEL84 and not for the first time either.

My amp stays turned off most of the time when I'm not using it. I only turn it on a few minutes before use, but then will keep it on all of that day ( or evening) until i go to bed at night, or leave for work usually at about 8:30 pm ( permanent night shift worker).

I turned it on this morning and an unholy racket issued forth from my speakers. It was a very loud grumbling and humming sound. Turning the source select to 'mute' ( and all the other selections ) had no effect, also turning the volume down to zero ( or any other setting ) also had no effect.

I switched the amp off at the mains switch and the noise eventually stopped.

I gave all of the valves a 'wobble' in their seats, to hopefully give the contacts a bit of a clean and tried again. The noise returned but this time was more severe, on switching the amp off again ( panic mode on) the speakers were screeeching and screaming very loudly ( source @ Mute, Vol @ zero).

I removed the two Brimar ECF80 and re-fitted the original EI ECF80. switch the amp on and everything was quiet as normal. I tried the two Brimars again (after gently dropping the onto the floor carpet to give them a bit of a jolt) and again the amp worked fine with no horrible noises.

This isn't the first time the amp has made uncontrollable noises such as this, which is a worry, especially if it is left unattended as i fear it might trash my speakers.

Any idea's ?

[andrew ivimey]

dry joint(s) around the ecf80 sockets - or the little goblins who do all the work in the valves are fed up.

[Richard]

I've had exactly this when trying nos valves and it was dirty valve pins.

Easy test is to put them in and rock them around to see if there's any noise. Then try moving the EI with their clean pins for comparison.

Best remedy I found is cleaning the pins with a glass fibre pencil.

Rich

[systemx]

Yup. and a dose of switch cleaner in the valve holders does the power of good. Don't use WD40 unless you are very carefull, the heat of the valves makes it go all brown and looks nasty.

[Sid and Coke]

Just to follow up on this one.

If i grabbed the nipple at the top of the valve and gave the valve a rock around in the valve holders, the Brimars made all sorts of horrible noises, the EI valves didn't.

I took the Brimars out, gave the pins a good clean with some very fine (8000 grade) micro mesh abrasive cloth, then cleaned them chemically using De-Oxit D5 contact cleaner.

I then placed the cleaned valves back in to the holders, switched on & moved them around again and didn't get a peep from them this time, not a sausage.

Thanks for the help guys, every day is a school day.

Despite these mineor niggles i still think it is the best piece of H-Fi equipment i have ever bought, still really happy with my purchase. Valve amps, especially self build ones are definately more hands on than a 'shop' item but thats part of the charm for me, probably why i still prefer to listen to Vinyl records, even though i actually own more CD's and digital media....

[John Caswell]

Hi all,
Be very careful of switch cleaner as some types leave a conductive residue. I don't think it necessary to clean valve pins with any sort of abrasive at al, a good squirt of IPA and a glass fibre brush is really all that is often needed.

John - Dr John