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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

#26 pre amp

Nice overview, Thomas!

My own personal favorite is the Sparton balloon 26. Clean and clear but with a touch of warmth. Sparton made their own tubes for a while and then outsourced to RCA; not sure who made my pair, but the plate structure is a bit different from the RCAs I have.
 
Hi.
My Pre UX-226


Line Stage
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Power Supply
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19803587340_ee17cfdf95_c.jpg


..
 
Dear Sir,

Hi I'm in the process in asking a builder to build a good pre-amp for me as I'm not technically inclined. Initially I was determined to select an Aikido but after looking at this page, my mind changes a little.

Some questions
1) How does this compare to Aikido, sound quality wise?

2) I'm not an experienced builder but I'd be providing a schematic for a friend ( an experienced one ) to build. Hence, I would want a schematic that is as direct as possible so that to make it as hassle as possible. Which one should I choose?

3) Which are the more expensive parts that I have to take into account for this project as sky is not unlimited but I have a budget of say $1500. Would this be enough?

4) Is there any "problem" that would be difficult to solve ( i.e humming etc ? ) should I encounter it?

5) Any maintenance/biasing required as an when?

Sorry for so many questions. Thanks in advance.
 
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Joined 2004
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My #26 tube preamp is -almost- cost no object (TVC, Elma swithes, V-Cap capacitor, Shinkoh and Riken resistors etc.) project, but the total cost is below 1500 USD (about 1000-1100).

Most effective parts:
- TX-102 TVC (it's unnecessary if you use good -for example TKD, Noble- potentiometer, or leave it);
- Elma 24x switch (it's unnecessary if you don't use TVC);
- Elma input switch;
- 100nF V-Cap teflon capacitor (use cheaper ones -for example russian FT-3-);
- AZ1 mesh rectifier tube (use good solid plate rectifier tube);
- Power supplies -HT and LT-;
- teflon tube sockets, silver connectors;
- Good -I prefer globe tubes- #26 tubes. ST tubes are cheaper.

As you can see it's a two box design (HT and LT supply, preamp).

I use regulated HT (Salas SSHV2 regulator) and Rod Coleman's V4 heater regulator in the preamp box (medium sized heat sinks needed).

Tube is heater biased, anode load is CCS (cascode DN2540 FETs). Heater bias resistor (10R 50W DALE non inductive 10W dissipation) large heat sinks is old computer CPU passive ones.
 

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BTW, how scarce is the 26 tubes? I did a quick search at epay, not much available.
What are the equivalence?

There are no equivalents.

But I would use the 4P1L. I built my first 26 preamp in 2008 and it lasted until about 2011 in many different versions. I then went over to the 4P1L - more dynamic, better treble. And I stopped using line stages and just used a 2-stage amp. Simple as that. The first stage can be used as a line stage, of course. But the output stage is better than any 2a3 or 300b design I built, and there were several of them. With its generous mu of 10 the 4P1L can be used in a 2-stage amp, and that solves a lot of issues.
 

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There are no equivalents.

But I would use the 4P1L. I built my first 26 preamp in 2008 and it lasted until about 2011 in many different versions. I then went over to the 4P1L - more dynamic, better treble. And I stopped using line stages and just used a 2-stage amp. Simple as that. The first stage can be used as a line stage, of course. But the output stage is better than any 2a3 or 300b design I built, and there were several of them. With its generous mu of 10 the 4P1L can be used in a 2-stage amp, and that solves a lot of issues.

It depends of your entire setup. I don't do the same combo if I use my 2A3 amp, Citation II or SS amp. Add speakers matching...That's another game!