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Old 30th September 2003, 01:06 AM   #1
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Default Any good #26 line amp designs?

Does anyone have a good #26 line amp design they would care to share?
I have a set of 150H chokes I would like to use for plate chokes. Any recommended plate voltages? Any help here would be appreciated.

Joe
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Old 30th September 2003, 09:15 AM   #2
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Hi,

Here's Jim De Kort's design for you:

# 26.

And one using an OPT as plate load from Denmark:

26 WOT

Cheers,
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Old 30th September 2003, 09:33 AM   #3
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Hi,

And yet another one, this time resistively loaded:

Chris Brady's preamp.

Cheers,
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Old 30th September 2003, 11:54 AM   #4
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Frank

Thanks for the fine examples of the 26. Do you have any words of wisdom before I tackle my last line stage? From what I hear the 26 is the worst to work with. I would like to use up my 150H chokes with this until I can get Barcelona to answer my email requesting prices.

Do you have any words of wisdom in regard to plate voltage and Dc supply for the heater?

Joe
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Old 30th September 2003, 12:39 PM   #5
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Quote:
Originally posted by burnedfingers
I would like to use up my 150H chokes with this until I can get Barcelona to answer my email requesting prices.
Email Kevin at K&K as there are some special order LL1667 that can be ordered gapped for 8 or 10mA IIRC and are probably around the 300-350H mark. I beleive they're the same price, but you might have to wait till his next shipment, but do check with him over the logistics. That's basically how the Oz distributor works so I guess he'll be the same.
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Old 30th September 2003, 02:17 PM   #6
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For another twist on 26 line stages you can check out the one I did a couple of years ago. Look in the schematics section down towards the bottom.
Gary P's DIY page

The choke loaded version used 2 150Hy hammond 156C's per channel. The dual chokes extended the frequency response on both ends of the spectrum. The double inductance of the chokes in series increased the bottom end. The capacitance is cut down as the interwinding capacitance is effectivly 2 caps in series for half the capacitance extended the high end.

Filament supply is a OTT dual battery setup. While the preamp is running on one set of batteries, the charger is charging the other pair. The batteries swap about every half hour. Allows long (indefinate) run time on small batteries.

Gary
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Old 30th September 2003, 09:16 PM   #7
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Hi,

Quote:
Do you have any words of wisdom before I tackle my last line stage?
It's also quite likely going to be the last you'll build...it can be that good.

My word of advice would be:

Watch out for microphony. Use rubber grommet shockmounts on the UX-4 sockets.

Now that Gary mentions it I do recall him using the Hammonds as he describes...somehow it just didn't turn up in my Google search results.

Another weakness is the heater's susceptability to hum...no problem if you go for GPs' clever solution.

With attention to detail in the right places this could be one of the best preamps ever.

Cheers,
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Old 1st October 2003, 11:46 AM   #8
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Thanks for the very fine examples of the 26. I will probably build one of each to see which I like the best. I will use grommets to mount the tube sockets as well as the transformer and chokes. In other words take no chances the 26 will pick up any stray vibrations or hum from chassis components.

Does anyone have a favorite plate voltage and current draw for this tube? Gary P have you built a 26? If so would you care to share a picture?

Thanks everyone for the helpfull hints. Brett could you send me a link or something as I haven't heard of K&K

Joe
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Old 1st October 2003, 12:16 PM   #9
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Quote:
Originally posted by burnedfingers
Brett could you send me a link or something as I haven't heard of K&K

Joe
Forum
http://www.audioasylum.com/forums/KandK/bbs.html

Homepage
http://hometown.aol.com/kevinc927/index.html
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Old 6th October 2003, 04:21 AM   #10
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I think I am going to tackle the Choke loaded design from Gary P
diy page. I am going to try this without the battery circuit as I think it can be done with a regulated 1.4 volt supply. I put together several regulated supplies and they are quite clean and certainly deserving of a try. I assume that a well sinked LM317T should be up to the task.

I have a very nice stepped control (value 10K) and was wondering if it was feasable to use it on the tail end of the line stage. Is this a recommended way to do things? Can someone help me with the calculations here? Also, it doesn't list the B+ voltage on the plate. Any ideas here?

Joe
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