KEL84 - Sounding dull & lacking lower end

[AKlein]

I've had my KEL84 for around 11yrs, it was my first kit amplifier build.

It has been used extensively over this time period and over the last couple of months or so there has been a noticable decline in the higher and lower frequencies, leaving just the middle which is also sounding a little vague.

The most obvious solution I thought to myself was to replace the valves, but this has had no effect. (?)

Then, I opened it up and noticed one of the coupling capacitors had come off at one end!, great, I thought, soldered it back on and......urm, wasn't that either. The bass was a little more balanced but still some way off.

Any ideas or suggestions? I really do love this little amp and would really appreciated any pointers.

Thanking you in anticipation.

[Phil Y]

Hello AKlein,
Did you replace all the valves or just the EL84s ?
Did you buy new or NOS.
Secondly, do you have a multimeter ? If so go over the amp checking all the voltages just as you did when you first built the amp.

Phil.

[AKlein]

Thanks for the reply Phil,

I have replaced just the EL84's, the ECF80's remain (not the original Edicron ones though).

The EL84's were new JJ's.

I do have a multimeter, but all voltages are as per the WAD instructions/testing manual (?)

I did think about the ECF80's, but also, perhaps the caps are starting to perish. Maybe these need replacing also?

Regards,

Adam

[Phil Y]

Hello Adam,
The JJ EL84s should be fine, I just asked because some valves out there are being sold that look just old rather than NOS.
How old are your ECF80s ? I have just replaced mine at 6 - 7 years because they were getting fairly tired (I have a valve tester). Though that said, they just sounded flat and lifeless rather than actually rolled off at the top and bottom.
If you still have the original "orange drop" coupling caps I would think they will be fine. Unless abused they should last pretty much forever.
If the PSU caps had gone badly you might expect hum. That only leaves the cathode bypass caps. These could be past it and audio grade ones do sound a lot better than standard ones.

Just to rule a couple of things out, do all inputs sound the same ?
Also, this may sound a silly thing to ask but are you sure you have not made any other changes to your system lately.

That is all I can think of right now, maybe someone else will have some ideas.

Phil.

[AKlein]

Hey Phil,

I have Tungsgram ECF80's and they will be getting on for around 8 or so years old. I'll order some replacements just as a general precautionary measure.

My coupling caps are Audio Note Copper Foil and these will be around 8 years old also, the original orange drop ones are long gone i'm afraid.

No hum with my unit at all, and the bypass caps are BG's, again around 8 years old.

Not silly at all Phil, but no, no equipment changes of any description.

So, plan of action so far is as follows, which I will undertake:

1) Replace ECF80's.
2) Replace Coupling Caps, albeit not AN ones, probably Clarity Cap.
3) Replace PSU Caps (Dublier ones with kit) with BC Component ones.
4) Replace all electrolitics with Panasonic FC's

In effect, give the amp a service. This will take a couple of weeks or so, so I will update all then, with some nice pictures.

Thanks very much Phil, very much appreciated.

Does anyone else have any suggestions over and above the plan of action items?

Regards,

Adam

[Richard]

Originally Posted by AKlein

Then, I opened it up and noticed one of the coupling capacitors had come off at one end!, great, I thought, soldered it back on and......urm, wasn't that either. The bass was a little more balanced but still some way off.

Hi both, yes sounds a good plan. Small signal triodes may last around 10 times as long as output pentodes but these ECF80s also have a pentode section and I don't really know how long they last.

The above made me smile. Perhaps we'd expect such a fault to be very obvious but I had one which was only running on one output valve also and it still gave around 4W in single ended and didn't sound obviously bad at reasonable volumes!