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All DHT Phono Stage
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Nick
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PostPosted: Tue Feb 23, 2010 8:06 am    Post subject: Reply with quote
Just for fun, why not current reg the filaments and include the cathode resistor to give the required bias?
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Andrew
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PostPosted: Tue Feb 23, 2010 8:59 am    Post subject: Reply with quote
SteveTheShadow wrote:
OK a bit further on now

Here is a proposed HT regulated supply for one of the pairs of DCC90s;
this courtesy of a National Semiconductor application paper (I'm not clever enough to do my own,
or that inclined to reinvent the wheel Smile)


Steve


Ah the Maida reg, Nat Semi Data Sheet 47.

Steve, please take a look at the power supplies for the LCR and Colin's C3g phono.

I have been here, know what bits get hot, and even have a vero board layout.

As you say, no point re-inventing the wheel, the info should all be in those threads.

-- Andrew
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Andrew
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PostPosted: Tue Feb 23, 2010 9:01 am    Post subject: Reply with quote
Mike H wrote:
Sorry only just seen this!


Andrew wrote:
Hang, maybe I'm missing something here, but how does the valve know what's behind the regulator?

I believe it doesn't Question ~ hopefully the desired result is that the regulated output (+ & –) looks like just another battery


So, why do you need separate TX's? Wouldn't separate regs do it, which is what I think Nick is alluding to.

-- Andrew
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Nick
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PostPosted: Tue Feb 23, 2010 9:39 am    Post subject: Reply with quote
Yes, doing it that way you could have a common ground.
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simon
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PostPosted: Tue Feb 23, 2010 1:02 pm    Post subject: Reply with quote
Nick wrote:
Just for fun, why not current reg the filaments and include the cathode resistor to give the required bias?

Can't quite imagine how that would look? The filaments in this phono aren't straightforward, at least to me anyway. Or am I imaginging it more complicated than you mean?

Interesting project Steve - very interested to see how lots of regulation compares to big passives and batteries. As another alternative, my phono using John Broskie's pcbs has a ICXY CCS protecting a LD1085 - really quite straightforward to implement and seems to work well enough. It's probably not appropriate for me to post the circuit here, though it'll be buried on Tubecad somewhere, but I could send you a scan if you're interested?

I think Will tried choke loading the anodes to maximise the gain, but I think he struggled with it a bit. Might be worth considering to avoid the extra stage? And if you're going to add another stage why not another DCC90? There's a challenge for you Smile.
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Nick
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PostPosted: Tue Feb 23, 2010 1:28 pm    Post subject: Reply with quote
Well, you could either put both heater supplies in series, input valve connected to ground, second valve to current regulator. Parallel the heaters in each valve to require 220ma @1.4v, then feed them both from a 220ma current source.

or keep them separate and use a 220ma current source for each valve. To get the bias for the second stage add a 5R9 resistor between the heater and ground to create the 1.3v bias.

If needed I will draw it out tonight.
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Mike H
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PostPosted: Tue Feb 23, 2010 1:30 pm    Post subject: Reply with quote
Nick wrote:
Yes, doing it that way you could have a common ground.

OK gotcha, cos it's 3V with a 1.5V 'tap' so to speak. Not sure how to do it though.

.
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Mike H
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PostPosted: Tue Feb 23, 2010 1:32 pm    Post subject: Reply with quote
No I do. I think ....
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Nick
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PostPosted: Tue Feb 23, 2010 2:01 pm    Post subject: Reply with quote
I will try and draw it out tonight. I could always be wrong.
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simon
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PostPosted: Wed Feb 24, 2010 1:01 pm    Post subject: Reply with quote
Right, I think I understand, though I really must get my head around sinks and sources one day - the current source bit lost me.

I have the valves to have a go at this one day. I think I'd be inclined to have separate current regs for each valve, unless I can find some big batteries that will give 1.4V - listening to Steve's I got the impression, and I might be wrong, that the filaments didn't like being starved.

And three separate regs for the HT. With anode chokes.

But all that regulation might kill what I really like about this phono so who knows...
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Mike H
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PostPosted: Wed Feb 24, 2010 1:58 pm    Post subject: Reply with quote
I thought I had the heater regs arrangements sorted out for a minute, but no.

Why can't one 3V reg supply both valve heaters in series?

.
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