Valves, I think I'm starting to understand what the fuss is about.

[Reid Malenfant]

I've just checked for audible hum and hiss and I can't hear any hum and just a slight bit of hiss when the volume is cranked all the way up. So I'm happy with that.

The only slight cause for concern so far is that the mains transformer is almost too hot to touch. I've read that they run hot in the KEL84 but I'd prefer to lower the temp if possible. Does anyone know if attaching heatsinks to the transformer sides with heat conductive epoxy will affect the working of the transformer at all? I wouldn't have thought so as aluminium isn't ferrous but I thought I better check to be on the safe side. Cheers.

That'll be fine Dave, though it's the windings that you want to keep cool really

[HighFidelityGuy]

That'll be fine Dave, though it's the windings that you want to keep cool really

Ok thanks Mark. I might look into that later.

It looks like I spoke too soon about hum. I've just connected the amp up to my main speakers and I get a hum through both channels. I guess the cheapo Argos speakers weren't sensitive enough to pick it up. So I need to look into that issue. It sounds like it's about 100Hz, so I don't know if that's anything to go on. I've got a feeling it's going to be either the signal input wiring or the feedback wiring that's at fault. The original wire was shielded but I've used twin solid core twisted together. So perhaps it's picking up interference from one of the rectifiers or something.

[Reid Malenfant]

Try using shielded wire where it was used previously, it was probably used for a reason

[HighFidelityGuy]

Ok thanks. I always struggle to find good quality but reasonably priced wire to use for internal hookup. We spend tons of money on good quality cables to go between equipment so it seems only sensible to use cables of the same quality inside equipment. It would be great if Mark Grant sold his G1000HD cable unterminated as I'd use that. Up until now I've not had a problem using 5N silver wire off eBay but I guess this amp creates more EMI than other things I've worked with. It could just be a wire routing issue though. I had to run the left channel feed back wire quite close to the heater supply rectifier as I ran out of cable.

I've tried moving the input wire further away and that hasn't helped so It might be the feedback wire. It's going to be a real pain to get to the place on the PCB where this connects now so I think what I'm going to try first is sheathing the existing cable from the other end. I have some shielded microphone cable that I should be able to strip the internal cores out of. I'll try that and report back in a bit....

[Reid Malenfant]

It would be great if Mark Grant sold his G1000HD cable unterminated as I'd use that..

So i'm guessing you haven't PM'd him to find out if he would then

Don't ask & you certainly won't get

He's a nice chap to deal with & after a bit of discussion supplied me with 20M (i think) of unterminated DSP 2.5 mains cable

[DSJR]

I get wonderful results from van damme screened cables. The single double screened has a handful of silver strands in it from memory and this seems to work well. The wire costs less than £1.50m and is really good - honest!

[HighFidelityGuy]

So i'm guessing you haven't PM'd him to find out if he would then

Don't ask & you certainly won't get

He's a nice chap to deal with & after a bit of discussion supplied me with 20M (i think) of unterminated DSP 2.5 mains cable

I've not asked Mark. I decided to just use what I had seen as I'd had good results before. I'll send him a PM and see what he says.

I get wonderful results from van damme screened cables. The single double screened has a handful of silver strands in it from memory and this seems to work well. The wire costs less than £1.50m and is really good - honest!

Thanks, I'll keep that in mind.

Well I tried shielding the existing cable and that didn't work. There wasn't enough room inside the microphone cable. So I decided to just use the microphone cable for the feedback wire. Unfortunately it hasn't changed anything. So I need to try something else. First I'm going to do some searching on the Word Design forum to see if anyone else has had a similar problem.

[HighFidelityGuy]

Aaaaaaaarrrrgggg, I don't believe it, I think I've just wasted ages replacing the feedback wire when there was nothing wrong with the amp.

I decided to double check that the hum wasn't being caused by a ground loop, so I started pulling out cables going into my attenuator and when I got to the one that comes from my AV amp the hum disappeared. So it was a fecking ground loop all along. What a ball ache.

I've got an idea how to fix this by plugging the AV amp into a different socket but for now it's staying unplugged the fecking fecker. Right I'm off to Burger King for a belated dinner as I can't be arsed to cook.....

[HighFidelityGuy]

I've now lived with my modded KEL84 for a few days and I must say that I'm really enjoying the sound it's making. I didn't do any critical listening for the first couple of days but during that time it sounded very good but a bit uneven, with a slightly bright top end and slightly too much mid-bass punch. These areas have now calmed down and the overall sound seems very balanced. I haven't done any direct A/B test between this amp and my solid-state mono-blocks but I had become quite accustomed to the solid-state sound. It seems at the moment that I can hear more detail through the KEL84, with the main improvement being that there seems to be more space around the notes, as if they were getting blended together a bit more by the solid state amps. This has produced a more airy sound that I like a lot. Bass is also improved, with a nice mid-bass punch and seemingly more control and clarity in the lower bass. The mid-range also seems clearer somehow which has made vocals slightly more realistic sounding. Overall the sound seems to be more detailed and even handed and just generally easier to listen to. Which is nice.

So the upgrades seem to have filled the main gaps I was hearing between my solid-state amps and the un-modded KEL84. Hopefully this really is the case and it's not just that I'm making myself believe it. I'll know better when I get one of Stan's switch boxes to do some proper A/B testing. I'll leave that for a while though so the KEL84 can run in a bit more. I think I'll have to look into getting some better EL84's to try as well.

I've really been surprised by just how much performance the KEL84 has to offer. I never thought a 15W valve amp could work this well with my speakers. Especially in the bass department. I thought 15W would be way too little to get this much bass but I was very wrong.

[DSJR]

Does the mains transformer still run very hot?

I tried the top models Graaf preamp at home a good few years ago (the sample KK wet himself over). On switch-on, the transformer buzzed like a swarm of angry bees, but was silent 20 minutes later. The thing was, that he casework got very hot and I really feared for the row of expensive oil-filled capacitors visible along the back of the case. A few years of regular baking this way must have shortened their lives I'd have thought.