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Another baby step with the LM3886...

Posted 24th November 2009 at 08:14 PM by Bas Horneman (Bas Horneman's diyAudio.com blog)

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It will take a while before the Baby Huey is done...

Posted 23rd November 2009 at 10:52 PM by Bas Horneman (Bas Horneman's diyAudio.com blog)
Updated 24th November 2009 at 05:01 PM by Bas Horneman

therefore in between I'll be posting progress on my LM3886 "gainclone"

I soldered the boards a long looong time ago. So no pictures. And I don't think anyone would want to see these boards soldered part by part. pcb's are boring in that way.

The build will be quick and dirty. But still something I could "live" with. Hopefully.
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Delivery

Posted 20th November 2009 at 07:48 PM by Bas Horneman (Bas Horneman's diyAudio.com blog)

Look what the mailman/woman dropped at my casa.

A matched quartet of GM70's (Almost ashamed at how little I paid for them) GM70's are for a SE GM70 amp with MQ parafeed iron.

And the 500R trimpots and 0,22uF caps for the Baby Huey.

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Ordered 500R pots for the driver stage.

Posted 18th November 2009 at 09:27 AM by Bas Horneman (Bas Horneman's diyAudio.com blog)

And while I was at it I saw some 0,22uF Epcos MKV from the same seller. The Epcos will do duty as coupling cap, as I've seen good reports (anecdotal) on them.

I asked Ian (gingertube) what the 470R resistors were for. Because I figured the CCS would take care of everything of the balance.

Here was his answer:
Quote:
The 1K pot is to set balance in the diff amp. The resistance in the triode cathode degenerates the tube gm (Ia/Vgk). Sweeping the pot wiper from side to side varies the amount of degeneration on each of the 2 triodes until they match. This is the minimum distortion condition for the diff amp. As we don't want to throw away gm un-necessarily we don't want those resistance values too high - just high enough to be able to adjust for matching behavior.
For a random sampling of 12AX7 and ECC803S that I had, 1K was too much, 100R was'nt quite enough so I dropped the 470R on each side of the 1K pot which effectively makes that pot about
...
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Slowly but surely making progress

Posted 16th November 2009 at 10:36 PM by Bas Horneman (Bas Horneman's diyAudio.com blog)

I have used a diy fluid for drilling for the first time. Used bicycle chain oil...water and detergent. Quite happy with it. Drilled the largest hole yet. And it looked almost professional.

Also a photo of the oak enclosure after it was treated with boiled linseed oil. The oil makes the oak enclosure look a lot better, it really brings out the grain. As usual I don't have "before" pictures to show the difference. (the pictures below had a partial coat already)

I'm not sure what to seal the wood with. Suggestions are welcome. Right now I'm thinking about shellac.
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Output tubes's CCS's (bias blocks) completed.

Posted 15th November 2009 at 12:14 AM by Bas Horneman (Bas Horneman's diyAudio.com blog)

sans bypass cap.

Measure 380mV accross a 10R resistors. Therefore the CCS is set to 38mA.
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First holes have been drilled...

Posted 19th October 2009 at 09:07 PM by Bas Horneman (Bas Horneman's diyAudio.com blog)

Mock up pictures. The wooden "boxes" are from Ikea and will cover the output transformers. The single power transformer shown will be put under the chassis.
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Building the Baby Huey EL84 PP

Posted 19th October 2009 at 04:08 PM by Bas Horneman (Bas Horneman's diyAudio.com blog)

As a way to kick off my project. I decided to pour the Baby Huey thread into a wiki form. So that I would have all "necessary" info in one spot. And hopefully so would other prospective builders.

Baby Huey PP EL84
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