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Author Topic: Anyone here familiar with the B&W L-1000-A amp?  (Read 836 times)
K1ZJH
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« on: November 27, 2017, 08:56:59 AM »

I am curious to know what the neutralization stub (NS on the schematic) looks like.  Length, and proximity to tube plates.

I don't see it shown in the photos in the manual.

Pete
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W1QJ
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« Reply #1 on: November 27, 2017, 12:29:44 PM »

Good Question.  I don't see it in any of the photos of the amp.  I do see it drawn on the schematic.  I wonder if it is really there?  If it is there it is hard to see in any photos.  If it is there it will probably look like a simple metal stube about 3/8" wide and probably 3" long insulated from the chassis and situated right in between the tubes.  I had an LPA-1 years ago and they look almost exactly the same and probably are.  I don't recall that stub on mine.  It's been a long time.
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N4UE
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« Reply #2 on: November 27, 2017, 12:43:11 PM »

Hi Lou. Decades ago, I bought a HB 50 MHz amp built by a retired machinist. It was based on an Swan conversion by Bill Orr. It was in a very old issue of CQ. Before he passed, Bill and I exchanged snail mail about the amp..... It has the vertical plate between the pair of 3-400Zs, later replaced with 3-500Zgs.
The ground end of this plate is a 2 turn coil inserted into an inductor in the input circuit. It works great, but is retired, because it is just plain huge.

73
ron
N4UE
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K1ZJH
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« Reply #3 on: November 27, 2017, 02:07:38 PM »

Lou, I.m betting it is in the recessed  section where the tube socket is below chassis, or that the wire gimmick wasn't needed and not installed by the factory.  Grid to plate capacitance is minuscule in that tube.
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W1QJ
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« Reply #4 on: November 27, 2017, 03:39:26 PM »

From what I can see the LPA-1 that I had is basically the same amp (RF deck) as this l-1000a.  I don't remember seeing that stub but maybe it was there.  It is basically there for neutralizing I'd suppose.  I would think 2 tubes would not be enough to need it.  The Ameritron AL-811 with 3 tubes doesn't, but the H with 4 tubes does.
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N4MPM
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« Reply #5 on: December 02, 2017, 06:23:59 PM »

No stub in my L1000A.
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K1ZJH
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« Reply #6 on: December 03, 2017, 07:35:08 AM »

No stub in my L1000A.

That is consistent with other reports... so if the feedback winding for the NS exists on the filament choke, it must be in the recessed socket area below chassis and not visible.

No big deal, I am just curious as to how they did it. 

Pete
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W1QJ
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« Reply #7 on: December 03, 2017, 10:03:40 AM »

No stub in my L1000A.

Yup my LPA-1 I don't think had one either.
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