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DHT line stage 26, 01a or 101d

cygnus x1

Member
2006-09-25 1:19 pm
I have to start out by saying that I currently have a 26 line stage and are pretty happy with it. I remember a long time ago I tried a 10 and liked it but could not deal with the hum. Something about a thoriated tungsten filament that appealed to me. So now looking for my next fix. Thinking 01a or even a 101d (not thoriated). May even go back to the 10? I don't need a lot of gain. Anyone try either of these?
 

euro21

Member
Paid Member
2004-09-17 12:16 pm
Budapest
Some years ago I regularly use #26 preamp (filament biased, CCS loaded, parafeed output to S&B TVC) and very satisfied with it....but IMHO TT (thoriated tungsten) filament is the another world. I'm in love it. :)

I tried #01 (UX201). It has wonderful tone, but (for me) driving capacity (I use TVC) is problematic (see Ale's site Slew Rate (Part 2) | Bartola Valves ).

I continuously use 841, 10/10Y/VT-25, 801/801a/VT-62 tubes in my VAS, CF and output stages with excellent results.

The topology is usually simple, but no free lunch. Separated (filament transformer, raw DC PSU and -I use Rod Coleman' type- regulator) filaments, optionally filament bias, significant - 20-30mA -anode currents, silent HT PSU(s), large heatsinks etc.

My humble rule: every 1 kg amplifier needs 10kg PSU. :)

I'm on the finishing state of 801 (or 10 and variants) preamplifier.
Filament biased (Rod Coleman V7 regulator), gyrator loaded (Ale's design), capacitor (V-Cap CuTF) coupled. The volume control is one TKD potmeter in the input.
The PSUs is in the other box: two raw filament supplies, one common HT (300-320V, cLCLC).

I will try it with graphite anode 801 tubes.
 

cygnus x1

Member
2006-09-25 1:19 pm
I built my 10 linestage after I saw an article in Sound Practices issue 16 (a log time ago). DC heater. 4:1 transformer coupled. Although I could never get all the hum out of it, it really did sing. I may have to revisit that now, with Coleman reg and FET CCS.
 
Some years ago I regularly use #26 preamp (filament biased, CCS loaded, parafeed output to S&B TVC) and very satisfied with it....but IMHO TT (thoriated tungsten) filament is the another world. I'm in love it. :)

I tried #01 (UX201). It has wonderful tone, but (for me) driving capacity (I use TVC) is problematic (see Ale's site Slew Rate (Part 2) | Bartola Valves ).

I continuously use 841, 10/10Y/VT-25, 801/801a/VT-62 tubes in my VAS, CF and output stages with excellent results.

The topology is usually simple, but no free lunch. Separated (filament transformer, raw DC PSU and -I use Rod Coleman' type- regulator) filaments, optionally filament bias, significant - 20-30mA -anode currents, silent HT PSU(s), large heatsinks etc.

My humble rule: every 1 kg amplifier needs 10kg PSU. :)

I'm on the finishing state of 801 (or 10 and variants) preamplifier.
Filament biased (Rod Coleman V7 regulator), gyrator loaded (Ale's design), capacitor (V-Cap CuTF) coupled. The volume control is one TKD potmeter in the input.
The PSUs is in the other box: two raw filament supplies, one common HT (300-320V, cLCLC).

I will try it with graphite anode 801 tubes.

I have nothing to add ... this is the bible.
 

vega65

Member
2007-11-13 4:03 pm
"Yes, we can make the 10 line-stage hum-free now.", Thanks to Rods regulators!!!

This one is "Silent"
(Tribute's irons in psu, and stepdown opt with tapped secondaries for volume control)
Spectrum from output with 2,8v signal in,
 

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I agree with Ale about the tonality of the 01A. And thanks to Rod you can built now DHTamps/preamps hum free, but most important with no sound degradation. Also thanks to Ale, one can built them at lower cost and great sound using his gen2 gyrator.
I recently built a switchable preamp between 01A and 26. Little mod and 10Y can be used too. The trick is to find the operating point that have the same Ua and switch the Rk and R sense of Coleman.
 
10Y, 4P1L, 112a, 30sp, 26 etc are all great options but for me best tone is 01a. You can add an output follower to ensure you can drive more demanding loads. Sound isn't degraded in my experience. Good luck
Ale

Ale and I have set up various listening tests to compare 4P1L, 26 and 01A line stages. we've both built several examples of all three.

Ale is quite right - if you want to build a damn near perfect line stage, it's his 01A Gen 2 design. He has some PCBs and I wouldn't hesitate to contact him and start the build. It's the current state of the art.

http://www.bartola.co.uk/valves/dht-pre-amplifier/01a-preamp-gen2/
 

euro21

Member
Paid Member
2004-09-17 12:16 pm
Budapest
I recently built a switchable preamp between 01A and 26.
Hi Radu,

Do you like it? :)
01-26 switchable preamp.jpg


Abszero said:
Little mod and 10Y can be used too.
I'm afraid it's a bit more than "little mod". :p
I use my 10/801 preamp with 320-340V B+ (between 260-270V and 25-30mA operating points) and 8R bias resistor.
It's another animal than "low voltage/low current" preamps as 01a or 26.
 

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I do like that I can switch between two wonderful sounding tubes.

Regarding the mods for 10Y: I was thinking more of a lower operating point something like 180V, 15mA, -7V. Then need a little twitch to the Rsense, keep Rk at 7ish ohms and replace 2SK170 with J310. I never tried 10Y as a preamp, so I am not sure that the operating point that I proposed is a good one. Looks good on the paper though.

Cheers,
Radu
 

euro21

Member
Paid Member
2004-09-17 12:16 pm
Budapest
I also use in my 801 preamp J310 (and 1kV depletion MOSFET) in Ale's gyrator.

I prefer higher (25-30mA) anode current.

The tone -IMHO- "smoothens" about 25mA (I mainly use graphite anode 801s with moderate -7..8W- dissipation). The "steel" plate tubes (10, 10Y, 801 a etc.) "requires" higher anode current (in my 841-10Y-801a PSE amplifier I use this tubes at 30mA).

In this region -if the tube is in good working condition- the 3th distortion spectrum line is decreasing a little (according to my measurements), second is dominated (at line levels), so overall tone is become cleaner.

It's my experience, in my system, appropriate for my taste, so strongly subjective. :p
 

euro21

Member
Paid Member
2004-09-17 12:16 pm
Budapest
I assume it's somewhat like the 26 schematic you posted above, but with different operating points, etc.?
Right.
I'm a lazy man, so rarely make changes in proven solutions. :)

It's a bit oldest schematic (only for simulations). In the reality the B+ and the anode current is a bit higher, so operating point is about 260V/30mA.

I will start soon separated topic as "10/801 preamplifier", where updated schematics -preamp, HT, LT supply etc. and pictures about the constructions) will be shown.
 

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