Kora Amp and Preamp Repair

Better yet spend $20 on a custom T-Shirt that reads:

Beat me up
Take me home
& call me Peggy.

You must be a glutton for punishment. Let us know how it ends this time, by hammer or drop from a great height.

I'd have to be asking myself if there isn't some inherent fundamental design flaw that is causing the problems. I've read interviews with more than one designer/engineer that feels there are any number of poorly executed amp designs that are fundamentally flawed and subject to constant failure.

Your story reminds me of my AudioValve monos, made in Germany. They sounded wonderful when they worked, but ... poor reliability & costly repairs. Techs told me there were design issues, which I took that with a grain of salt, but several problems were due to just plain poor soldering. The amps were 11-12 yrs old and had cold solder joints here, there and everywhere. Fix one problem, another popped up somewhere else ... A moving target ...

Eventually I just cut my losses: 'got them repaired to spec, at high cost, sold them, and haven't looked back. Besides the money, the whole thing took up too much mental disc space. And there are many, many great sounding amps in the world ...

I can fix them. You can message me through Agon or contact me through the Alta Vista Audio website bigkidz email address. I am in Montville, NJ.

Your story reminds me of my AudioValve monos, made in Germany. They sounded wonderful when they worked, but ... poor reliability & costly repairs. Techs told me there were design issues. I took that with a grain of salt. But several issues were due to just plain poor soldering. The amps were 11-12 yrs old and had cold solder joints here, there and everywhere. Fix one problem, another popped up somewhere else ... A moving target ...

Eventually I just cut my losses: got them repaired to spec, at high cost, sold them, and haven't looked back. Besides the money, the whole thing took up too much mental disc space. And there are many, many great sounding amps in the world ...

I know this is an old thread but the record must be set straight. I stand corrected about Kora'a reliability. Kora is actually very reliable and resilient if owner/serviceman use it right.

SPECIFICALLY, ALL THOSE ISSUES WERE DUE TO THE WRONG TUBES BEING USED.

EL84M IS NOT THE SAME AS EL84. I REPEAT: EL84M IS NOT THE SAME AS EL84!

This will explain why Kora's preamp and DAC products (Eclipse, Hermes, Crescendo) are almost indestructible than their power products (Flash, Explorer, Cosmos, Galaxy, et al).

Kora's power amp products use EL84M which has a different bias. If you put regular EL84 (or the misleading EL84S) into Kora, you will risk damaging it! Fuses will blown, smoke may come out. You name it.

I finally realized the past malfunctioning Kora amps I encountered were all with EL84 from previous owners! To make it way worst, multiple repair shops tweaked the schematics to make them not blow up using EL84 --- of course that's not a true fix. Such wrongly repaired Kora become ticking time bomb.

It is very sad that the EL84M is grossly misunderstood, that some tube-rolling hungry owners may not bother to notice such critical difference, and some audio repair shops made the same wrong assumption and thus made things worst.

So do yourself s favor. If you are owner of Kora power amp and/or integrated amp products, please make sure you are using EL84M, not EL84.

Hope all of you enjoy the magical Kora sound as much as I do.

I have a Kora Galaxy Reference amplifier, and, stupidly inserted 4 Svetlana tubes. The right bank red lights came on, I switched it off, replaced the tubes with the Sovtecs, and it now works again, though the red lights are on. Any clue who can fix this.......?

David

I have a Kora Galaxy Reference amplifier, and, stupidly inserted 4 Svetlana tubes. The right bank red lights came on, I switched it off, replaced the tubes with the Sovtecs, and it now works again, though the red lights are on. Any clue who can fix this.......?

David

It is true that the EL84M is more robust, due to the fact it can handle high anode voltages better than the regular EL84 can.  Kora used transformers that are designed for 115V primaries when we commonly have 126V available today. This means that for nominal 400V rails, the Koras actually have 440V rails, which causes the tubes to over-dissipate. 

When I repair Koras I lower the rail voltages, and I reduce the Q point a bit, so that any EL84 can be used (even though the "M" remains better).  This eliminates this issue.  Most of my audio buddies have Koras that I rebuilt many years ago and they have had zero issues and rarely need new tubes.  And they sound incredible.

As for putting Svetlana tubes in, this is not the problem.  The reason an issue came up is because you must adjust the bias when you retube these amps because they have a fixed bias - they are not autobias (cathode biased) like most other amps on the market today.  You can get much better performance with fixed bias, but it requires knowledge and skill to replace the tubes.