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Balanced Differential Linestage with Low Mu - perhaps DHT ?
Balanced Differential Linestage with Low Mu - perhaps DHT ?
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Old 8th November 2017, 01:42 PM   #21
audiowize is offline audiowize  United States
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It's actually quite difficult to compare an anode choke against a CCS, as you need to raise the B+ a bunch to use the CCS properly compared to the choke.
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Old 8th November 2017, 01:50 PM   #22
Blitz is offline Blitz  Germany
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Really ? Kevin's CCS needs about 10-15V to operate and an anode choke loke the LL1168 has 340ohm per windings, in my case maybe 25mA for the 7119 gives 340*0,025=8,5V , so we talk about a difference of max 5-6V...I can live with that.
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Old 8th November 2017, 02:48 PM   #23
audiowize is offline audiowize  United States
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You can swing above B+ with a plate choke, but you can't do that with a CCS. This will always make the plate choke sound a lot better than the CCS when you are just substituting one for the other unless signal levels are tiny.
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Old 8th November 2017, 03:07 PM   #24
Blitz is offline Blitz  Germany
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Aaaaah, now I got the point, sorry for being too slow. I never used a CCS sofar as anode resistor/choke replacement before. So, the CCS should be run more at a level of an anode resistor to have enough dynamic headroom ?
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Old 8th November 2017, 03:28 PM   #25
artosalo is offline artosalo  Finland
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Quote:
...to have enough dynamic headroom ?
Are you still talking about Linestage ?
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Old 8th November 2017, 04:14 PM   #26
ErikdeBest is offline ErikdeBest  Switzerland
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Balanced Differential Linestage with Low Mu - perhaps DHT ?
Quote:
Originally Posted by Blitz View Post
Well...in the older days there have been schematics and even white papers and I believe this is tremendous...I would regard the way Thomas is sharing today more like as a teasing...for potential customers on his build quality and for us diy-guys to use our brains and figure the stuff out by using a forum like this.

Typically his circuits are very, very simplistic ...for very good reasons. So, it should not be too hard to fogure it out...
A while ago I asked Thomas how he would do a PP amp, and he mentioned differential with chokes in the common cathode, that would be at least one choke per channel. He shows 4, maybe he will connect both in series or parallel?
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Old 8th November 2017, 05:53 PM   #27
Blitz is offline Blitz  Germany
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Well...I guess you want to do some maths to check...:

A 801a would need at least 15mA current (actually better 30mA), lets say he runs it at 400V. (PLease see his nice explanations here: VinylSavor: The search for that 'magical' operating point ) rp might be 4K if you are optimistic a bit (that is a result I see with many of those I have tested). 4K with an inductance of 100H for one full LL1668 gives us -1db at 25Hz or -3db at 6Hz. In SE.

340 Ohm winding resistance would give us a voltage drop of 340*0,015=5.1V. The bias you need at 400V is actually more like -35V at 15mA...all just for one tube.

With two chokes in series we would bust the defined limit of the chokes in the picture as this would mean 30mA over two chokes where each is speced only for 15mA in series with a voltage drop of approx. 20.4V.

With two chokes in parallel...this would reduce inductance to 50H effectively, which gives us still a -3db point of 12Hz...and he used not the 25mA, but the 15mA version of the LL1668, so maybe 150H/2 ?
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Old 10th November 2017, 07:44 AM   #28
RhythMick is offline RhythMick  United Kingdom
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Originally Posted by artosalo View Post
Here the pre with LM317 CCS.
Really appreciate that thanks.

I'm going to ask a dumb question now, but just one of those weird things I need to get straight in my head.

Given that the valves are DHT, how best to configure the filaments ? Let's assume AC for now - simply run 5V AC across the 2 valves in parallel ?
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Old 10th November 2017, 01:50 PM   #29
artosalo is offline artosalo  Finland
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Given that the valves are DHT, how best to configure the filaments ? Let's assume AC for now - simply run 5V AC across the 2 valves in parallel ?
I would not even try to use AC, only DC-voltage.
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Old 10th January 2018, 09:55 AM   #30
RhythMick is offline RhythMick  United Kingdom
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Originally Posted by artosalo View Post
Here the pre with LM317 CCS.
I plan to use a pair of DHTs, perhaps 26s. It may not work well, but I'd like to try it.

Firstly, I've never used a CCS before (or any solid state) - is there a primer on how to calculate the resistor network required to provide 12mA through the CCS (each 26 approx 6mA) ?

Secondly, I've never used a valve model in LTSpice. If I PM you would you be happy to mail me that model to give me a start point ?
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