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Nick
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#181

Post by Nick »

Yep, thats it.

He hosted the image on photobucket and then inserted a link to the image.
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#182

Post by Mike H »

Dave the bass wrote:^PICTURE EDITED^ due to pencil operative being dense.
Image


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#183

Post by Mike H »

Ask a daft question but is it really necessary to have such ee-norm-ouse value inductors for the first stage anodes?


Ah wait a minute, probs because 400H @ 50 Hz = 128 kilohms

Blinking flip ...

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#184

Post by Nick »

Yep, you are forming a RL high pass filter between the ra of the valve and the inductor, so for the first triode in a 6em7 with a ra of 40k, the -3dB with 400H will be 16Hz
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#185

Post by Dave the bass »

Nick wrote:Yep, you are forming a RL high pass filter between the ra of the valve and the inductor, so for the first triode in a 6em7 with a ra of 40k, the -3dB with 400H will be 16Hz
Yup, as I found out when I just stuck one 200H choke in I lost bass. 2 in series brings it back but 'EM' doesn't seem to be an ideal candidate, that led to this thread actually didn't it, good lord! We're still on topic! :lol:

Now then, 6DN7's ra is much lower isn't it at 9K. Thats going to affect the -3dB point I'm guessing.

IIRC from earlier in this thread the formula for working out the 3dB point of RC networks was f-3db = 1 / (2 x PI x C x R).

What one formula would you use for working out f-3dB when ra and inductance is involved Nick?

Back to DRD'ing. Does DN or EM lend itself better to to DRD topology?

If its raining over the weekend I could try that cct.

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#186

Post by pre65 »

Nick wrote:Yep, thats it.

He hosted the image on photobucket and then inserted a link to the image.
Aha - I see now, I wondered why there were 4 ways.
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#187

Post by Nick »

RL formula

f-3 = R / ( 2 * Pi * L )

Where in this case R = ra, and L is the size of the choke in Henry,
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#188

Post by Dave the bass »

Thanks Nick, so using that formula with 6DN7's 1st triode and 400H load I calculated 3.58Hz is the f-3dB point.

...and 'cosI've got a calculator in my hand ... Halving the inductance to 200H gives 7.16Hz.

Conclusion, with 6DN7 I don't really need 400H do I? 200H would do really.

Using 6EM7 using 1 200H choke gives a f-3dB of 31.8Hz and 2 chokes gives 15.9Hz.

Hmmmm.

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#189

Post by Nick »

Hmmmm.
Yep, it can, all those are well above 100hz :-)
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#190

Post by Dave the bass »

Nick wrote:
Hmmmm.
Yep, it can, all those are well above 100hz :-)
Arf, I said Hmmmm not Hum :lol:

That DRD cct Phil has drawn be OK for 6DN7 and 6EM7 Nick?

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#191

Post by Nick »

No 6em7, may need some values changing for t'other one. Should be doable though. Start with the op points you need and go from there.
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#192

Post by Mike H »

Dave the bass wrote:Conclusion, with 6DN7 I don't really need 400H do I? 200H would do really.

Using 6EM7 using 1 200H choke gives a f-3dB of 31.8Hz and 2 chokes gives 15.9Hz.

Hmmmm.

DTB
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#193

Post by simon »

Dave the bass wrote:Thanks Nick, so using that formula with 6DN7's 1st triode and 400H load I calculated 3.58Hz is the f-3dB point.

...and 'cosI've got a calculator in my hand ... Halving the inductance to 200H gives 7.16Hz.

Conclusion, with 6DN7 I don't really need 400H do I? 200H would do really.

Using 6EM7 using 1 200H choke gives a f-3dB of 31.8Hz and 2 chokes gives 15.9Hz.

Hmmmm.

DTB
YMMV Dave but I found that lowering the anode choke F-3 on my 26 pre from 8Hz to 4Hz made quite a difference in filling the bottom end out.
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#194

Post by Dave the bass »

simon wrote: YMMV Dave but I found that lowering the anode choke F-3 on my 26 pre from 8Hz to 4Hz made quite a difference in filling the bottom end out.
Ooooerrr, thanks Simon.

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#195

Post by pre65 »

So are we saying that the anode chokes for a 6DN7 should be 400H (2 x 200H ) like DTB currently uses or would one 200H be enough.

I was going to order some anode chokes and need to know how many.
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