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Old 15th November 2009, 09:54 PM   #1
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Default DRD amplifier with CCS?

First Post ever for me;

I want to build a DRD/free lunch/ monkey type of amplifier; but i want to try to use a CCS instead of the large (80H) coil. I have done some drawing and thinkin' but have some concerns:

- Is it possible at all? I know that Manfred Huber had a schematic of some sort which could resemble such an amplifier, however his site is vanished, and I cant find any copies of his schedules.
- During "power up" doesnt the output tube fully conduct till the driver tube settles in? I dont want to break the DHT (a jj2a3) and the OPT.

Anyone some thought about this?
Greetings, Paul
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Old 15th November 2009, 10:39 PM   #2
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Quote:
Originally Posted by pauldune View Post
I want to build a DRD/free lunch/ monkey type of amplifier; but i want to try to use a CCS instead of the large (80H) coil.
Cheap Lunch?


Quote:
Originally Posted by pauldune View Post
- During "power up" doesnt the output tube fully conduct till the driver tube settles in? I dont want to break the DHT (a jj2a3) and the OPT.
Use a CCS on the cathode of the output tube and you have nothing to worry about -- just be sure it is bypassed either to ground or to B+ (i.e. Ultrapath) with a cap.
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Old 15th November 2009, 10:44 PM   #3
pointy is offline pointy  United Kingdom
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he's in outer space.............

Manfred Huber

or is he.......?
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Old 15th November 2009, 11:14 PM   #4
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Haha; on "free lunch" i didn't search...

However, did you ever build that thing?
and if you did, how did it sound?
I dont care about the diminished voltage swing. I can always use a higher V++.
The 2a3 has a mu of 4; so for about 300v pp, 75v pp should be enough...
For a input voltage of 2V rms, a mu of 14 in the driverstage (because of the css load of the driver, close to mu amplification should be possible, and low impedance driving too) should be sufficient.

As I am biasing the 2a3 (jj2a3-40) at 100mA with a V++ of 450V, the bias voltage is app. -50v.
So 100v tt is possible with an ideal CSS; as I only need 75v tt to get the 300v tt swing on the output tube, this should be OK.

If i'm making any thinkin' errors, please correct me...

gr. Paul
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Old 15th November 2009, 11:16 PM   #5
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Ha ha, I think in that post he answered from some distant galaxy...
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Old 16th November 2009, 02:54 PM   #6
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Hmm seem to unable te edit my own messages. That first one was in reply to dsavitsk, and the second one to pointy. Hope I didnt offend someone...

In the first I meant to say that i didnt search for "cheap lunch".

I really should learn not to post at time i should be sleeping...
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Old 16th November 2009, 10:35 PM   #7
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No, I never built it -- eventually I just bought the plate chokes and then stuck them in a drawer and moved on to other projects From Electra-Print plate chokes are only $42 each.

As you know, the limiting factor is the required voltage drop over the CCS. With a 50V bias, if the CCS requires 25V, then you only get 50V p-p of swing. So, the CCS design matters a lot, and my sense would be a single chip 10M45 or the like would be a good tradeoff. Note that if you do overdive the output stage, clipping will be nasty. Also probably worth some experiments to determine what happens if the source of the CCS chip goes positive w/r/t/ the drain -- you don't want a situation where a big transient blows the amp up.

Last edited by dsavitsk; 16th November 2009 at 10:40 PM.
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Old 16th November 2009, 11:08 PM   #8
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. Also probably worth some experiments to determine what happens if the source of the CCS chip goes positive w/r/t/ the drain -- you don't want a situation where a big transient blows the amp up.
It is a 10M45 i'm going to use; i think these only need a few volts to work correctly. As for the source/drain going positive; i can't think of a situation were that could happen. the 10M45 is sitting between the cathode of the 2a3 and the anode of the 12BH7 in my case. And of course connected to the grid of the 2a3.
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