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Old 7th January 2010, 04:52 PM   #1
robmil is offline robmil  United Kingdom
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Default Conrad Johnson ART preamp question.

Here goes.......

as a complete novice and have only worked with solid state stuff...can someone help answer this question.

A friend has a Conrad Johnson ART MK2 preamp. It uses parallel ECC88s. The manual says the tubes will last a mere 3 months if left on at all times.

The question is - why 3 months? Is this to do with the B+ voltage which is 160v? The heater voltage is 12.6v. I've looked at the spec and the ECC88 heater is rated at 6.3v. If you tie pins 4 and 5 together (heater pins) do you then run them at 12.6v?

thanks for not killing me in advance

Rob
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Old 7th January 2010, 04:59 PM   #2
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by robmil View Post
Here goes.......

as a complete novice and have only worked with solid state stuff...can someone help answer this question.

A friend has a Conrad Johnson ART MK2 preamp. It uses parallel ECC88s. The manual says the tubes will last a mere 3 months if left on at all times.

The question is - why 3 months? Is this to do with the B+ voltage which is 160v? The heater voltage is 12.6v. I've looked at the spec and the ECC88 heater is rated at 6.3v. If you tie pins 4 and 5 together (heater pins) do you then run them at 12.6v?

thanks for not killing me in advance

Rob

Just the number of hours of operation before the tubes start to degrade audibly in their performance. FWIW I do not recommend any tube component be left operating continuously unattended or when not in use for more than a couple of hours. This is both for safety and longevity of components including tubes.

A lot of electrolytic capacitors are rated at only a couple of thousands of hours at their rated temperature, and even at a fraction of that in continuous operation might last only a few years.

Finally there is a real safety issue as well if a component fails and the power fuse does not blow for some reason. I have had more than one instance where had I not been in the room or nearby a tragic outcome may have been the result.

For critical listening normally less than an hour of warm up should be required for the maximum glory of which the particular device is capable. Longer than that and there is probably a design issue IMHO.
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Old 19th January 2011, 03:32 PM   #3
sajti is offline sajti  Hungary
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I like the simplicity, and elegance of the ART preamplifier. So I decided to build something like the ART. I did some simulation, and the result is quite good:
4pcs. of E88CC (8 triode parallel), with 6.2mA bias each. Distortion is 0.00075% with 100kohm load, and 1V output! Output impedance is about 800ohms. The distortion with 800ohm load, and 1V output it 0.1%. With 100kohm load, and 10V output is 0.05%
I know that is only simulation, but it looks promising!

Sajti
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Old 19th January 2011, 04:06 PM   #4
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If B+ has a dedicated switch keeping filament on would prolong tube life. For power saving purposes filament in standby mode can be one fourth of normal operational voltage.

B+ especially if it goes on right away with filament that wears off cathode the most.

Amprex PQ 6DJ8 claimed to be the best ECC88 very hard to find NOS however. 6922 is another option.
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Old 19th January 2011, 04:20 PM   #5
DF96 is offline DF96  England
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Keeping the heater on with no anode current may cause sleeping sickness (cathode interface) problems, unless the valve has a special cathode which avoids this.
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Old 19th January 2011, 04:25 PM   #6
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Quote:
Originally Posted by DF96 View Post
Keeping the heater on with no anode current may cause sleeping sickness (cathode interface) problems, unless the valve has a special cathode which avoids this.
It is a typical myth from Russian online forums. Typical myth from American online forums is that all tubes feel better when B+ is delayed by relay...
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Old 19th January 2011, 04:37 PM   #7
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I am owning Italian Graaf 13.5 II that has B+ delay.
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Old 19th January 2011, 04:38 PM   #8
sajti is offline sajti  Hungary
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Quote:
Originally Posted by DF96 View Post
Keeping the heater on with no anode current may cause sleeping sickness (cathode interface) problems, unless the valve has a special cathode which avoids this.
E88CC can handle it.

Sajti
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Old 19th January 2011, 04:40 PM   #9
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Cathode poisoning, aka Sleeping Sickness is real. It just doesn't seem to be happening much in our amps. This was discovered decades ago in tube powered computers that could often leave a tube unused for long periods of time.
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Old 19th January 2011, 04:40 PM   #10
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Quote:
Originally Posted by suntechnik View Post
I am owning Italian Graaf 13.5 II that has B+ delay.
Now all myths are international!

I mean,
1) B+ relay delay saves lives of tubes;
2) Keeping cathode hot with no B+ saves lives of tubes.

Actually, both are bad for them. First cause big transient currents and cathode poisoning, second causes cathode poisoning only, but of greater degree.
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Last edited by Wavebourn; 19th January 2011 at 04:44 PM.
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