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Old 21st January 2003, 01:33 AM   #1
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Default Availability of 6C33C tubes? I need some for OTL amps

Hi

I have heard some worrying news about the availability of 6C33C tubes, some people say that they are not manufactured anymore. Does anyone know the facts?

I use them in my OTL amplifier and today I am building a couple of these for my friends, it would not be so good if the tubes are unavailable soon if they would be needed for re-tubing.

My OTL is here: http://www2.gol.com/users/tube/otl.html

Regards Hans
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Old 21st January 2003, 02:05 AM   #2
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Hi,

Seems to be widely available. If the production does cease, Russian military jets are going to be without radar.
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Old 21st January 2003, 05:53 AM   #3
Colt45 is offline Colt45  Serbia
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I have a friend that can supply them for $15-20, let me know if that will work..
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Old 21st January 2003, 07:26 AM   #4
dhaen is offline dhaen  Europe
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Default Availability

Hi,

These things have to run out sometime.
Gintaras (who ships worldwide) seems to still have them at the reasonable price of $10.95 ea.
http://www.kwtubes.com/

Cheers,
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Old 21st January 2003, 07:19 PM   #5
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Default FROM INSIDE THE INDUSTRY.

Hi,

The 6C33-C has not been in production for the passed 4 years.

However,don't panic...prices have never been lower at current dealers and stock levels are still estimated at 750.000 units worldwide.

The lack of breakthrough for audio use is one factor for the current hold,the war thread in the East however is such that the factories keep all tooling ready in case war comes into play.

Nowadays even the US-Army uses these types in various applications.

Relax...if we can still unearth NOS tubes from the 40's to this day you can be rest assured the 6C33-C will still be around for the next 20 years at least.

Ineteresting your SRPP OTL.
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Old 21st January 2003, 09:47 PM   #6
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Frank,

Thank you for this valuable information, that is exactly what I wanted to know, if stock is that much I can understand it shoudn't be a problem to source tubes for 2 or 3 amplifiers in the future.

I have used my OTL now for ~ 3 years and during this time it has been very stable and I have not needed any re-adjustment of bias. I have heard that many people experience problems with 6C33C but as I have understood it, it depends either due to bad sockets or that the tubes are not run in properly. I adjusted my sockets so that the connectors is pressing on the pins as much as possible and I also let the tubes run for one week with heaters only before switching on B+.

2 of my friends, one here in Japan and one back in Sweden really like this amplfier so I promised to build 2 more.

Regards Hans
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Old 21st January 2003, 10:05 PM   #7
dhaen is offline dhaen  Europe
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Default Omoshiroi

Han's,

Your comments about the 6c33 are very interesting. I had been put off using them for such a design because of the worry about stability.
May I ask:
What kind of sockets have you used?
&
What is the reasoning behind the 1 week burn-in?

Cheers,
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Old 21st January 2003, 10:15 PM   #8
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Default ALLOW ME PLS.

Hi,

Quote:
What kind of sockets have you used?
Icecold,the septar socket is not up to carry the heater currents.

Quote:
What is the reasoning behind the 1 week burn-in?
This is a low mu,high transconductance valve operated at high current.
It will need weeks to stabilise and change even after that...John you should know your teletubes.

Moreover the septar will have a hard time carrying this kind of heater current,it will eventually quit its' job.

Cheers,
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Old 21st January 2003, 10:23 PM   #9
dhaen is offline dhaen  Europe
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Frank,

I was aware of the heater current problem, which is why I posed the question.

I also wondered whether it was characteristic drift, and how far they drift apart.

Your comments on the OLT thread are not clear, with regard to biasing.

Has the beer kicked in yet.

Cheers,
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Old 21st January 2003, 11:26 PM   #10
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Hi,

The sockets I use I bought here in Japan from the same place from where I got the tubes. These sockets are not the same as ordinary SEPTAR types as they have an extra U-shaped spring that push the split connectors together, (I have used ordinary Septar sockets without these extra springs when I built RF amplifiers with YL1070 a long time ago). The sockets I use in my OTL I assume come from Russia as the tubes, the tubes where delivered in original boxes, (bad quality card board type).

The reason I did a one week burn in is that was recommended in the build instructions I got together with my 6C33C SE amp kit from SAN-ei, this amp was designed by Mr Dakesue who was the first one who imported 6C33C to Japan, (renamed EC33C)in the seventies.

As Frank says the 6C33C being a high transconductance tube is bound to show more drift than a lower transconductance tube like 300B, the distances between the catode and grid is smaller and therefore any mechanical tolerances or thermal drift, (where by these mechanical dimensions changes) will show up as a comparably larger drift in GM, (GM is inversly dependant on cathode to grid distance)

I measured some drift of bias current when I used my SE amp so therefore I use the burn in method also in my OTL and it seem to have worked well.

The tubes I use in my OTL is from Ulianov production, (they have Ulianov marking). I use 250mA bias current in my OTL so it works in class AB.

Regards Hans
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