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Old 18th May 2006, 07:08 PM   #1
mourip is offline mourip  United States
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Default UX-226 Preamp

Hi,

Anyone out there running a 26 tube preamp or heard one. I have several 226's burning a hole in my pocket and am tempted to make a very simple preamp. I have read that it can be hard to make them quiet. I have previously built a 71 amp and really like the sound of these old DHTs. I started with AC filaments but ended up with DC since I was using headphones and had a hard time taming the humm. AC sounded better to me. Has anyone tried an SMPS for heaters? I have already seen the VT52 web page projects and would probably use that for a start.

The alternative that I am considering is an Aikido but I love the globe tubes...

Any opinions out there?

Thanks a lot,

Paul
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Old 18th May 2006, 11:50 PM   #2
arnoldc is offline arnoldc  Philippines
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My friend hoarded 26 tube in various forms (gave me a pair which I haven't collected) and built a preamp. It hums loud, and he has tried various tweaks but I can never convince him to use battery for the filaments.

It sounds glorious on his system (he's using a type 50 amp) and he's tolerating the hum. Me, I can't. So if I finally collected my pair from him, I would do battery filament, or at least DC.

I'd use diyAudio's CCS to load it on the anode or sink on the cathode, I don't know yet. Just thinking out loud.
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Old 19th May 2006, 01:32 AM   #3
mourip is offline mourip  United States
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Quote:
Originally posted by arnoldc
My friend hoarded 26 tube in various forms (gave me a pair which I haven't collected) and built a preamp. It hums loud, and he has tried various tweaks but I can never convince him to use battery for the filaments.

It sounds glorious on his system (he's using a type 50 amp) and he's tolerating the hum. Me, I can't. So if I finally collected my pair from him, I would do battery filament, or at least DC.

I'd use diyAudio's CCS to load it on the anode or sink on the cathode, I don't know yet. Just thinking out loud.
Thanks for the input. I am in the collecting stage for ideas and yours are very welcome. I went to your web page and saw the 417a/45 amp you made. Very nice. I made a very similar amp with a 417a and a 171 tube. I started with a Lundahl interstage but converted it to choke load the input driver instead. I made this one just as a headphone amp. I wish that I never sold it.

I love DHT's.

Best,

Paul
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Old 19th May 2006, 01:43 AM   #4
arnoldc is offline arnoldc  Philippines
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Quote:
I started with a Lundahl interstage but converted it to choke load the input driver instead.
A bit OT but I have vested interest I was thinking of going that way, using LL1660. Can you share your experience why you liked choke loaded over the IT instead?
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Old 19th May 2006, 02:11 AM   #5
mourip is offline mourip  United States
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Quote:
Originally posted by arnoldc


A bit OT but I have vested interest I was thinking of going that way, using LL1660. Can you share your experience why you liked choke loaded over the IT instead?
Boy, this is a little tough, mainly because I only remember that I prefered it. I tried a lot of things with that amp. I loved AC filaments but could not kill the humm. I ended up with DC filaments but put some small chokes in the filter. It sounded somewhere inbetween AC and DC. I also used battery bias on the driver tube. If I remember correctly I used the LL1660s also. I used an 80 for the rectifier. The rectifier tubes made a pretty big difference in the sound. Here are a couple of photos. If anyone out there has this amp let me know how you are liking it...

Click the image to open in full size.



Click the image to open in full size.
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Old 19th May 2006, 02:17 AM   #6
arnoldc is offline arnoldc  Philippines
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alright, thanks for sharing re: IT vs Choke

back to the topic- my friend is inviting me to his place tomorrow for some wine and steak i hope i don't get shy this time on the 26

it will be goodluck to us both on our 26 project
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Old 19th May 2006, 11:35 AM   #7
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I believe Kevin Kennedy got around the hum problem.

Like others here I also have a shoe box full of parts for this project. Haven't tried this yet but I am sure it will work. Without batteries too.

I ordered some Edcor transformers instead of the costly and hard to find HA-133's
Attached Files
File Type: pdf 26 line stage.pdf (44.4 KB, 746 views)
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Old 19th May 2006, 12:08 PM   #8
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Default Re: UX-226 Preamp

Quote:
Originally posted by mourip
Hi,

Anyone out there running a 26 tube preamp or heard one. I have several 226's burning a hole in my pocket and am tempted to make a very simple preamp. I have read that it can be hard to make them quiet. I have previously built a 71 amp and really like the sound of these old DHTs. I started with AC filaments but ended up with DC since I was using headphones and had a hard time taming the humm. AC sounded better to me. Has anyone tried an SMPS for heaters? I have already seen the VT52 web page projects and would probably use that for a start.

The alternative that I am considering is an Aikido but I love the globe tubes...

Any opinions out there?

Thanks a lot,

Paul
Give a look here,
a phono preamp (Loesch like) with 26 linestage.

http://www.teresaudio.com/haven/preamp/csb_riaa.gif

I hope this can help you
ciao cicero32
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Old 19th May 2006, 07:13 PM   #9
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I use variable DC bench power supplies for the filaments of my balanced line stage, which has four UX4 sockets which can take any DHTs that fit the socket. I like having the variable DC for filaments so I can try out different tubes, and there are plenty that fit besides the 26. Just dial in the voltage you want and off you go. Simple. I don't have hum problems with my speakers, which are about 87db efficient. I tried batteries but in my case they were no improvement. My PSUs are Thurlby Thandar, which is nice, but there are plenty of others cheap on ebay all the time. Useful things to have for filaments.
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Old 19th May 2006, 08:53 PM   #10
kevinkr is offline kevinkr  United States
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Other tubes that come to mind that will work well in this design include the UX112A/12A, and the 301/201/01. This design will also work with the 27 IDHT as well and its variants. Hum obviously is less of an issue with one of these..

It is really important to minimize magnetic fields around the tubes and transformers, and a quiet filament supply is a must.

I strongly recommend a separate chassis for the psu, that said it is possible to build one on a single chassis with good results.. I mounted the power transformer at one end of the chassis on top and the output transformers internally mounted on back and side panels about as far away as possible.

I recommend electrostatic shields around the tubes as unattractive as that may be..

The speakers I use are extremely efficient >103dBspl at 1W and there is no audible hum from this pre-amplifier with a power amplifier having in excess of 20dB of voltage gain.

Of the above types the 26/226 is by far the most common and easily obtained.

I noted the link to my schematic, and I am delighted that people are sharing it here, but please (!!) read the associated article which you can find through a link on my site. There is a lot of material about this design and what is needed in general to build one successfully. A number of my local friends have also built this design without serious difficulty.

edit: fix omissions
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