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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 8th April 2013, 08:55 PM   #1
mudchute is offline mudchute  United Kingdom
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Default Checkout double check.

Hi all,

I've just been tackling the checkout procedures.

With all the valves installed, speakers in place and powered up I'm getting a b+ of 459v.

R17 and R27 are putting out 36v each.

I went through Ty's checkout procedure to see if my tube of choice is working within its limits (Tung Sol 6L6GC STR reissues).

SO, with the parts list 560ohm resistors in place using ohms law (correctly I hope) I got 0.064ma.

For the dissipated power I took 36v from 459v = 423v then multiplied that by 0.064a gives 27.26w dissipated power.

Does that sound correct?

NExt up, the tube specs http://www.tungsol.com/tungsol/specs...r-tung-sol.pdf

If I'm correct, I believe I'm over the max signal plate current listed on the specs (in triode operation) as 44ma max, sound right? It has 66ma listed as the max plate voltage for tetrode, is it that one I should be going by?

But, max plate dissipation is listed as 30w so If I've worked that out I believe I'm ok.

Lastly, Georges simulations for my opt/tube/b+ combination (CXSE25-5k-8, 459v, 6L6GC) suggest I'm gettting close to the max abuse my tubes can take with the 560ohm resistor.

6L6GC 450 5000 437 37 560 66 27 3.95 7.1 0.4 3.21

So here's crunch time, if I've understood everything correctly would it be safe to say that the 560ohm resistor is a good choice for these tubes?

Last edited by mudchute; 8th April 2013 at 08:58 PM.
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Old 8th April 2013, 09:59 PM   #2
rknize is offline rknize  United States
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Yes, it looks like a good choice. The 30W max rating is what is important, as that is what the plate has to dissipate when the amp is idle. For a SE amp like this, the plates are thermally stressed the most at idle. When playing music, some of that power gets diverted to driving your speakers.

The plate current numbers are just examples of certain circuit topologies to give an idea of how the tube operates.
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Old 8th April 2013, 11:27 PM   #3
mudchute is offline mudchute  United Kingdom
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Thats great, thank you for checking that out for me. Everything to do with my understanding has now clicked into place!

Well, I can now report a happy amplifier which I have just wired up into triode with cfb and subsequently sounds superb. I'c can just sit back an enjoy for some time now (touch wood...)

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