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Steven123 23rd April 2011 10:20 PM

Hello I'm having some troubles finding the 10m45s from ixys. But is it possible to use the dn2540 wich i have without any change to the circuit of the tubelab SE or do I need to chnange something.
Or is there maybe anybody here who has some of those for sale and is willing to send them to Europe?

Kind Regards and thanks...

A desperate Tubelab SE builder...

Green77 24th April 2011 06:29 AM


I just finished my TSE with DN2540. Works greate :)
You will have to change the 330 Ohm resistor. I change it to 200 ohm and my 5842 is running with 10,7 mA..

What is the 5842 suppose to run at? 10mA? 12mA?


Steven123 24th April 2011 10:02 AM

I just checked the datasheet for the Raytheon 5842 and the max is 38mA amd typical operation is 25 to 27mA. So I think that 10,7 thqt you are running with is a nice value.
Thanks for your help.

zxx222 24th April 2011 07:41 PM

I had problem with purchase of 10m45s in eu, so made dn2540 cascode daughter boards for sse - not sure if it is safe, because B+ should be around 450 volts - that exceeds max voltage specification for dn2540. can't try it out, because I am still waiting for opt's from edcor. hopefully board will not burn during breadboard tests.

Green77 25th April 2011 06:43 AM

I'm thinking of putting in cascode DN2540 too.. what resittor value did you use?

zxx222 26th April 2011 08:07 AM

180 ohms - I read about this value in one of posts about dn2540 cascode. it will be necessary to measure current when amp will be running.

Tubelab_com 26th April 2011 12:59 PM

I have used the DN2540 in a TSE. I think I used a 180 ohm resistor. The DN2540 is rated for 400 volts but you will always drop at least 50 volts in the 5842, usually 150 to 200. That way the DN2540 sees about 250 volts.

The 5842 will dissipate too much power if cranked to 27 mA. I aim for 10 to 15 mA which keeps the dissipation to 3 watts if the plate voltage drifts to 200 volts with age. The 5842 has a wide tube to tube variation and does tend to drift with age.

Steven123 27th April 2011 10:35 AM

While I read everything here I also want to ask how important it is or not to use matched Tubes.

Steven123 29th April 2011 10:35 PM

Hello, since i'm still gathering parts for my tubelab SE i wanted to know how important the value for the Power Supply bypass cap is does it has to have 100uf and 370vac and what brands are availabale in these values.

Tubelab_com 30th April 2011 12:22 AM

Copied from an answer I posted about the SSE in another forum. THe same thing applies here except the choke can be rated for less current if you are building for 45's:

Just about any choke that can handle 150 mA or more will work. Aim for 5 to 10 Hy and a DC resistance between 100 and 250 ohms. I used a 1 Hy choke with 60 ohms of DC resistance in one of my amps because I didn't have space for a bigger choke. It still works better than a resistor.

The aux cap should be a motor run (NOT motor start) cap. Motor run caps are made for a very low ESR and work synergistically with the electrolytic to form a very good low cost solution. These are usually rated in AC volts and should be 370 VAC or higher. Any capacitance value from 40 uF to 100 uF will work. I usually shop for 80 or 100 uF motor runs on Ebay and have found them for $15 to $20.

Matched tubes are important in some P-P amps. Fanatics want them in SE amps but exact matching isn't needed. On the other extreme grossly mismatched tubes can make the two channels sound different.

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