nuvistors

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Mike H
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Post by Mike H » Tue Oct 04, 2011 3:07 pm

Silly question time ~ where in the circuit is this 295k? I'm looking at this ~ assuming it's still current:
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Mike H
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Post by Mike H » Tue Oct 04, 2011 3:13 pm

PS: FWIW for 560k I would have automatically assumed something like 0.1uF, did in the above calculator, got the –3 dB @ 3 Hz; for 295k, 0.22uF for about the same effect Image
 
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Mike H
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Post by Mike H » Thu Oct 06, 2011 6:25 pm

I'm still confused where 3.3uF fits into things. Image
 
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Post by cressy » Thu Oct 06, 2011 8:40 pm

the 295k is where the 300k is in the above circuit, it needed amending due to the change from its original form. originally it was done for the 7f8w which required 300k but the nuvistor needed 295 instead. the 3.3uf was subbed in for the 0.22uf output cap.

the input on the amp is a 50k pot so i put 25k in to represent the pot half open and it came out at 20hz f3 point.

i put the biggest resistor i had (560k) between the signal pin and earth tag on the output socket, seemed like a good idea to stop the output impedance changing

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Mike H
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Post by Mike H » Fri Oct 07, 2011 1:18 pm

Ah-hah thank you. :D That explains all yes.

If it helps my phono pre o/p is using 6.8uF ClarityCaps for the same reasons.

Yes you need a leak resistor of some sort across o/p socket otherwise if you turn it on before plugging it in, then plug it in the following amp gets a big SPIKE
 
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cressy
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Re: nuvistors

Post by cressy » Tue Jan 03, 2017 11:13 pm

Got some aluminium extrusions to re case it after nearly 6 years.
Image

Fascias will be walnut with copper tape on the back to maintain shielding, psu in one, circuit in the other. hopefully it will quiet it down some more

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Re: nuvistors

Post by cressy » Mon Jan 16, 2017 5:39 pm

Quick question re re casing the phono stage, usual best practice when using an umbilical is to put the last psu cap in the circuit enclosure.
As this psu has one of nicks mj regulator boards on the end of the psu presumably the reg board should be in the circuit enclosure?
Or would it be better to have the last cap and the board in it
Cheers ant

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Re: nuvistors

Post by Cressy Snr » Mon Jan 16, 2017 5:44 pm

Merln Blencowe reckons a regulator should be as close as possible to the circuit it is regulating.
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Re: nuvistors

Post by Ant » Mon Feb 12, 2018 7:23 pm

Possible dumb question.
I am severely out of practice with anything to do with this.
Given that the heaters for the 2ds4 nuvistor is 2v, is there any reason why I couldn't use a 2v sealed lead acid battery to heat them?

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Re: nuvistors

Post by jack » Sun Feb 18, 2018 11:44 pm

I believe 2V nominal SLAs are actually 2.1V and float charge up to 2.25V.

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Re: nuvistors

Post by IslandPink » Mon Feb 19, 2018 9:34 am

Easy enough to knock that down with a resistor or two.
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