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Old 8th January 2013, 03:01 PM   #2291
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Hi!

Quote:
Originally Posted by tyo94 View Post
Anyway, is there any info for good DHT tube beside 26 which can be used for good DHT preamp?
It is always important to look at it from the entire system. What is needed from the preamp. Gain? Low output impedance or both. Depending on that the tube chocie can be done.

My favorite for linestages is the 10Y / 801A family of tubes. I don't need much gain in a linestage so I can use these with step down to get low output impedance as an ideal driver for a TVC.

Other candidates besides the 26 would be the UX112 or if you want somewhat euphonic sound the UX201A. You could even use large triodes like the 211 or 845 if you are prepared to deal with them.

But again don't look at the tube alone. In my opinion the volume control is at least as important as the tube.

And of course many other possible choices

Best regards

Thomas
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Last edited by Vinylsavor; 8th January 2013 at 03:06 PM.
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Old 8th January 2013, 03:18 PM   #2292
tyo94 is offline tyo94  Indonesia
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Quote:
Originally Posted by Vinylsavor View Post
My favorite for linestages is the 10Y / 801A family of tubes. I don't need much gain in a linestage so I can use these with step down to get low output impedance as an ideal driver for a TVC.
Same with me, I don't need much gain. Currently, I do experiment by building preamp based on RE144 (gain: 10). I haven't try 26 yet, even though I already have the tubes. Some people said that this tube hard to handle when it comes to filament.

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But again don't look at the tube alone. In my opinion the volume control is at least as important as the tube.
Why the volume control has the same importance as the tube? Is there any specific reason? I am sorry for my silly question. I am really newbie in DHT Triode world.
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Old 8th January 2013, 05:45 PM   #2293
12B4A is offline 12B4A  United States
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Probably because everything that ends up being amplified by a system is what is developed across the volume control impedance interacting with the source and amplifying stage that follows.
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Old 8th January 2013, 05:58 PM   #2294
djn is offline djn  United States
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Is that also true with LED lightspeed volume controls?
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Old 8th January 2013, 06:49 PM   #2295
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Anyway, is there any info for good DHT tube beside 26 which can be used for good DHT preamp?>>

I've tried most DHTs. My favourite is the 4P1L in filament bias into a LL1660/18mA. This replaced my 26 preamp which replaced my 10Y preamp which replaced my 01A preamp which replaced my 1G4G preamp (nice tube, VERY microphonic).

I'm so pleased with the 4P1L I haven't used anything else for about half a year now, and usually tubes go in and out of fashion with me. But the 4P1L is a keeper.

71A, 112A, 46 and several others fell by the wayside. I do respect the 46 a lot but it demands more in filament bias than I'm willing to give it!
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Old 8th January 2013, 06:58 PM   #2296
mogliaa is offline mogliaa  United Kingdom
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I like the 4P1L, CX301a as well as 46 and 10Y. The latter two are quite demanding for filament bias, so not ideal if you're not willing to invest in the filament supply. I;m currently using the 46 in filament bias as a driver and the filament supply is simply: big!
The 4P1L can be a great poor man's DHT preamp valve. You can get excellent results with a mu-follower gyrator load circuit. Many have implemented this preamp with great results but if you can go for a LL1660/20mA you can achieve a very low output impedance without the compromise of the output capacitor. But then, the budget is different. The other advantage of the gyrator load is the PSRR.
I personally like the tone of the 01a and I'm running it with a gyrator load as well.
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Old 8th January 2013, 07:15 PM   #2297
iko is offline iko  Canada
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I wonder if anyone tried for preamp or driver duty anything excessive like a zero bias transmitting tube. I got a couple of NOS TZ40 that are looking for a good project. 7.5V at 3A heaters, amplification factor 62... Have no idea how linear they'd be at a few mA operating point.
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Old 8th January 2013, 07:58 PM   #2298
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Somebody made a 6AS7 preamp and reported negligable distortion. How it actually sounded I have no idea.
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Old 8th January 2013, 08:23 PM   #2299
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Hi!

Quote:
Originally Posted by tyo94 View Post
Why the volume control has the same importance as the tube? Is there any specific reason? I am sorry for my silly question. I am really newbie in DHT Triode world.
I regard the volume control as one of the most delicate parts in the entire system. When I tried transformer or autoformer volumecontrols the first time I never went back to resistive volume controls. That's already almost 15 years ago. This is not related to DHTs but preamp design in general. Although I prefer DHTs generally, I would take a IDHT linestage with a great TVC any time ober a DHT with a resisitve volume control. They need some care though. IME best driven low impedance through a step down transformer. For example 10Y thorugh LL1660 wired 4.5:1 into a Slagle TVC is awesome. Equally good the Tribute lineouts with the secondary implemented as volume control

Best regards

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Old 8th January 2013, 09:33 PM   #2300
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The conventional approach to the volume control is to do it in the analogue domain. My source - and I'm not alone in this - is in my computer, a Mac Mini. It's easiest for me to do all the volume controls in the digital domain. I'm constantly setting different levels for Youtube, TV, BBC iPlayer, iTunes, Spotify and so on. I sometimes have to do it very quickly if a programme sets its own volume control. So given this situation I've abandoned a volume control on my preamp. It's there but always on maximum, so effectively a 100K resistor to earth.

So as to have as little effect as possible in the digital domain, my whole system has enough sensitivity to allow me to turn the music up a little in volume if I have to, but no more than that.
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