Velleman K4000 amp

[Marc Schutte]

Hi all,

I am rebuilding a Velleman K4000 amp at the moment, after it vaporized 16
cathode resistors for the third time :-( . Does anyone know of any
upgrades/tweaks that i should try with this amp? This is what i've done so
far:

- Converted to triode mode
- Upgraded coupling caps
- Got rid of the ceramic caps
- Replaced all resistors with better ones to lower noise and improve
reliability
- Upgraded input/output connectors
- Replaced some internal wiring for lower hum
- Bypassed supply caps with 100n/630V
- Put in a blue power LED for better sound <LOL>

Any further tips are very welcome.

TIA, Marc Schutte

[Tom McNally]

I replaced each set of 4 of the 39 ohm cathode
resistors with 1 10 ohm 1 watt flameproof per
tube. It's a lot better, only blew one in a
year. I haven't moddded anything else yet.
Oh - did you replace those nasty Tesla EL-34's
with something better ?

... tom

[Marc Schutte]

Tom McNally <t...@mcnally.cc> schreef in berichtnieuws
37E05E59...@mcnally.cc...

> I replaced each set of 4 of the 39 ohm cathode
> resistors with 1 10 ohm 1 watt flameproof per
> tube. It's a lot better, only blew one in a
> year. I haven't moddded anything else yet.

I received the same tip from Remco (thanks). However, if i calculate the
amount of power dissipated by these resistors, the 1/4 w units should be
enough. Am i missing something here?
A Conrad-Johnson MV125 i'm repairing had the same problem, and it uses 5W
wirewounds.

> Oh - did you replace those nasty Tesla EL-34's
> with something better ?
>

Yep. Donated them to the recycling bin right after purchase (some 9 years
ago).

Marc Schutte

[Jorge Santos]

HI Marc
I think that you have a problem of instability and oscilation.
First as you have converted to triod mode you have increased the bandwith
of the
amplifier because the output transformers are now being drived by a much
low inpedance.
specially as the transformers of the 4000 are toroyds and as i have
measured have
large capacitance between primary and secundary.
You also say that you have (got rid of ceramics) but you dont say if have
changed
for other type of capacitors or you have simply retired them of the
circuit.
Has you have changed the cables for other types you also have changed the
capacity of them.
All of that changes have changed the open loop gain and phase of the
amplifier and then you have to try to estabelised it. For that you can try
change the capacitor across the feedback resistor and if it dont work you
may have to put a RC cellula across the plate resistor of the ECC 83 tube.
I hope it helps. I also have a Velleman K 4000 amp.
It's a pitty that Vellman dont make a less powered version with only a pair
of EL 34, because i think that paraleleds tubes dont sound so good.
Cheers
Jorge Santos
PORTUGAL.

Marc Schutte <lam...@removethisaha.nl> escreveu no art

igo <7rp4t5$spb$1...@news1.xs4all.nl>...

[Marc Schutte]

Jorge Santos <js...@ip.pt> schreef in berichtnieuws
01bf0039$fd08a000$155117c3@open...

> HI Marc
> I think that you have a problem of instability and oscilation.
> First as you have converted to triod mode you have increased the bandwith
> of the
> amplifier because the output transformers are now being drived by a much
> low inpedance.
> specially as the transformers of the 4000 are toroyds and as i have
> measured have
> large capacitance between primary and secundary.
> You also say that you have (got rid of ceramics) but you dont say if have
> changed
> for other type of capacitors or you have simply retired them of the
> circuit.
> Has you have changed the cables for other types you also have changed the
> capacity of them.

Oops, my fault. I should have mentioned that this problem has existed since
the first time i turned on this amp, some 9 years ago. So it has nothing to
do with the recent changes. Also it seems to be a common problem, not just
in my unit. Once every year/two years 1 channel quits. It also has nothing
to do with output power, it happens totally at random. This time i replaced
every part in the amp, and added some upgrades on the way. Its playing at
near full power for some hours now, without problems. But i still don't have
clue why it quits after some time :-(. Gues i'll know in a year's time or
so...

[vaalburg]

Hi Marc,

I also have gone trough many mods to my Amp. Shortly after I purchased mine
a friend of mine also bought one. The funny thing was that he kept on
blowing EL34's, now a total of four!. He and I basicly are now to the point
that both are equally modified amplifier, running in triode mode, class
A,same amount of bypass etc. There only remained one difference.
From the beginning I've always felt that underneath the topcover it was
getting too hot. This is not good for any component. Let alone drifting of
values.
In order to get some lower temperatures I raised the cover slightly by using
some extension bushings, M5 or M6 I forget. The kind you see on connectors
e..g. on your computer. I have yet to blow a resistor or tube. It may not
cure your problem, but it cannot do any harm as long as you do not raise the
cover too much for the sake of safety.

Good luck!

You also might give this a try
Marc Schutte heeft geschreven in bericht <7rqptg$8nh$1...@news1.xs4all.nl>...

[Vince Rhea]

Yeah, but what about the amp?

Vince

Jorge Santos wrote in message <01bf0039$fd08a000$155117c3@open>...

[Marc Schutte]

Guess that's why i had to start my own business to get a job...
<ROFL>

Vince Rhea <vin...@mis.net> schreef in berichtnieuws
FedE3.22846$Dk7.6...@newscene.newscene.com...

[Marc Schutte]

Thanks for the reponse.

This one's certainly worth a try. I looked through my notes of previous
repairs and found that the problem always begins with the same half of the
same channel, even after tube replacement. The only thing i can think of is
a problem in the bias circuit. I've replaced every part on the board,
including the icky bias pots. Better cooling could make life a bit easier
for them.

Thanks !

Marc Schutte

Vaalburg <vaal...@worldonline.nl> schreef in berichtnieuws
7rred5$eh3$1...@news.worldonline.nl...

> Hi Marc,
>
> I also have gone trough many mods to my Amp. Shortly after I purchased
mine
> a friend of mine also bought one. The funny thing was that he kept on
> blowing EL34's, now a total of four!. He and I basicly are now to the
point
> that both are equally modified amplifier, running in triode mode, class
> A,same amount of bypass etc. There only remained one difference.
> From the beginning I've always felt that underneath the topcover it was
> getting too hot. This is not good for any component. Let alone drifting of
> values.
> In order to get some lower temperatures I raised the cover slightly by
using
> some extension bushings, M5 or M6 I forget. The kind you see on connectors
> e..g. on your computer. I have yet to blow a resistor or tube. It may not
> cure your problem, but it cannot do any harm as long as you do not raise
the
> cover too much for the sake of safety.
>
> Good luck!
>
> You also might give this a try
> Marc Schutte heeft geschreven in bericht <7rqptg$8nh$1...@news1.xs4all.nl>...
> >
> >Jorge Santos <js...@ip.pt> schreef in berichtnieuws
> >01bf0039$fd08a000$155117c3@open...

> >> HI Marc
> >> I think that you have a problem of instability and oscilation.