• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

What tubes for a OTL tube amp?

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BUIZERD

BUIZERD

Member
Joined 2011
To Mr Popilin,

This is what Ralph Karsten from Atma has to say about preconditioning the tube's,

"If you are dead set on using American tubes, it is possible. The cathode resistance must be increased to a minimum of 5 ohms 5 watts (which is a good idea anyway). If the tubes are NOS they must be preconditioned for 72 hours to minimize arcing."

So i'm not sure what to do, preheat or not????
 
dady

dady

Member
Joined 2002
BUIZERD said:
To Mr Popilin,

This is what Ralph Karsten from Atma has to say about preconditioning the tube's,

"If you are dead set on using American tubes, it is possible. The cathode resistance must be increased to a minimum of 5 ohms 5 watts (which is a good idea anyway). If the tubes are NOS they must be preconditioned for 72 hours to minimize arcing."

So i'm not sure what to do, preheat or not????
Click to expand...

Thanks Buizerd for your investigation. Please if is possible to attach the link for read the entire article.
Best Regards and sorry for my Mad FACE
Welcome to Menorca. Many dutch come this year to (the)(My) Island.:)
 
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popilin

popilin

R.I.P.
Joined 2010
BUIZERD said:
To Mr Popilin,

This is what Ralph Karsten from Atma has to say about preconditioning the tube's,

"If you are dead set on using American tubes, it is possible. The cathode resistance must be increased to a minimum of 5 ohms 5 watts (which is a good idea anyway). If the tubes are NOS they must be preconditioned for 72 hours to minimize arcing."

So i'm not sure what to do, preheat or not????
Click to expand...

In old/NOS valves, the getter should be reactivated, then preheat is a must.
But not as proposed, ie powering the heater with no voltage between the cathode and anode.
Follow the advice of Wavebourn, is no coincidence that he is one of our superheroes in the forum.;)
My buddy Dady, said to me he would make an experiment with a thermocouple to heat the valves in an oven, to determine preheat temperatures and times.:)
 
W

Warmsound

Member
Joined 2009
Driver V4 Voltage

In the final MullardEL34 schematic, post 247 and attached, the effective Vpp voltage across the driver 6SN7 V4 is 620V. If the grid bias voltage on the final 6AS7s is in the range of -65V to -75V for Class A (say -70V), as delivered at the cathodes of V4, then the net voltage across V4 is about 380V. Seems awfully high as the 6SN7 spec sheet says 300V max. What am I missing?
 

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P

PET240

Member
Joined 2010
G'day TV7,

You just up the road from me.....

It'd be easier to read the thread, there is so much here, first 6-8 are really interesting, currently sorting my trannies for a set of M60 clones as the NO NFB attracts me.....a lot. I have a set of other OTL monoblocks in build stage as well when I came upon this thread. I could give you basics but it's worth the read.
Pm me and could have a yarn.

Cheers,

Drew.
 
BUIZERD

BUIZERD

Member
Joined 2011
As you can see in my avatar, I have them up and running for a while now, and i'm very satisfied, I have only a very small hum in the background, but that's because I do not have a balanced preamplifier.
Is it perhaps possible to share your talk with Ralph with us, we don't see him so often on this board lately.
 
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