DIY 26/UX-201a line preamplifier.

Hi!

During this CNY long holiday I have converted my 12a preamp into 26. This would be my prototype for 26/UX-201a project.

First, I will built it as 26. After fine tuned the circuit, UX-201a will be built. At last, Both design will combine into 26/UX-201a line stage. 

Previous 71a PSU reused for 26.


This 26 used Filament bias , so no cathode by pass cap needed. . All filtering would be done passively. As I did tried regulators on heater supply before, but I prefer the passive way. It's preserve DHT magic better !


100W Ohmite resistors being used as filament bias( Thanks, MThoi )
This resistor may go up to 80c during its operation.



I'm using a Solen 51uf capacitor as the last smoothing cap.
I will try out some NOS oil cap later stage.



Cheah

Wow! That thing looks like an industrial power installation.

I don't know much about tube components but this looks AWESOME!

Any chance I can get to listen to it one day?

Hi !

I replaced the 51uf Solens with NOS 8uf oil capacitors. 


With these 8uf oil cap, sound become more relex and open. I can here more detail then before.
Bass is lower and have better outline. I'm surprise that this 8uf cap can do so much for this preamp.

Cheah

Hi!

In order to make this preamp switchable 26 and UX-201a, I'm forced to try other cathode resistor. It's a bit difficult to accommodate 4 pcs of those 8" long Ohmite resistor in the line amp.
So, I decided to try Mills 50W non inductive wire wound resistors. A pair of 10ohm resistor will be use for 26. For 201a, 2 pcs( 10R + 12R) resistor will be series to achieve 22ohm.
 


When 26 is operating, the resistors will get very hot and heat up the whole aluminum rail. Soon, heat sink is added to it.



How does the Mills sound?
So far this 26 preamp sounded shut in. Sound staging is so much narrower than my 71a line amp. When change to Mills, suddenly sound staging open up, better depth and most importantly it's sounded more relax and analog.

Cheah

I put a 2w trimmer as temporary cathode resistor. This is convenient for me to get the optimum operating point for 01a and 26. Now the circuit is being finalized and the trimmer  will be replaced by 12W mills resistors.



Thomas Mayer did help me to make the top plates for my UX-201a/ 26 preamp.
They will share the same landscape style like my 10Y/801a preamp.

Cheah

Hi! 

The 01a/ 26 line amp had arrived, I can start building it.

Top plate for signal section.



PSU top plate.

This preamp looks so awesome compared to some sold out there. What's the final cost likely to be?

Hi STC,

Nice things have a price tag to pay.  

Please contact Thomas Mayer for a price quote.

Cheah

01a/ 26 preamp have been completed.



This preamp can use 01a, 12a and 26 tubes. These DHT tubes have their own strength. All of them sound very open. Microphonic level is very low as this preamp is equipped with sub plates for signal tubes.

Cheah

Cheah,

Congratulations, very nice - in 2 chassis.  Those look like Arcturus blue tubes?

Reg

Mthoi,

Thanks.
Those are Arcturus blue 012a tubes.

Cheah

Nice job, Noodle88. 

All you need to add is a nice nameplate to it. How about Noodle88 in chrome? 

STC,

STC,

Noodle88,

I saw your other creation too. Perfect job.Maybe you should also add your name to it. Like this...Hahaha
" />

STC,

That's look awful!

As I'm doing all these as a hobby, and have no business intention in it. Your tag suggestion is not needed here. Any how, thanks.

Cheah