Akarakrit Uamkruea, blogger and audio gear maker who passionate in vacuum tube, audio & music.
Producing electronics projects since high school. Seriously upgrade and modify vintage audio equipment for “Real Sound” concept.
He is a co-founder of Soundaries, all audio solution provider.
Experienced and lively explore the listening rooms & audio shops in Japan as his most favorite to do.

Thursday, December 30, 2021

Hard to Find Information Tube : LS7/CV1660

 I will try to measure vacuum tubes and post here frequently about tubes that hard to find information especially characteristic curve.

Hope this will help many people to discover good and reasonable price tubes on worldwide markets.

First is LS7/CV1660, Directly Heated Triode tube from England, ST shape with brown base.

Can make good sound small power amplifier or preamplifier.

Vf = 4V

If = 0.15A

Va = 150 Volts

Vg = -6 Volts

Ia = 10 Milliamperes

Mu = 12

Rp = 5,000 ohms

Gm = 2,400 Micromhos

Happy New Year 2022 to all of you.


Tuesday, August 31, 2021

Life Easy with Etracer ...

I think in Tube DIY world must know Tube Tracer that can trace tube's characteristic curves.

And now eTracer from Essues is latest smart vacuum tube tracer/tester.

You can access their website and study how it work, 


or find many of tube amp designers who using it and post on their blogs.

Essues Tech. supply it in kit (assembly/option), easy to assemble with 1 day man-hour ;)

Connect to computer via USB cable and fully control with program, easily change parameters

like filament voltage/current, plate voltage/current, load line, etc.

  Advantage that I really love are

1) match pair or match tube's sections with their characteristic curves not life time!

2) get accurate values to use in real circuit not common values from datasheet provided!

3) best for me is can plot triode curve from pentode tube that cannot find from any source!

Example : Triode curve of EL802 tube that never seen in any datasheet

I've measure and trace many tubes along 3 years that using this smart tube tracer/tester.

And know how easy to design if get the curves so I plan to post characteristic curves 

and typical operation values like plate voltage/grid voltage/amplification factor/plate resistance 

and transconductance of many tubes that common datasheet did not provided or not usable.

To be continue...

Thursday, May 6, 2021

Telefunken ELA V311 Transformation Part 1

I've got the first version of V311 power amplifiers more than 10 years. 

Already took out microphone transformers (2 channels in 1 can, using as stereo) 

to use as MC step up transformer, match with many cartridges especially Ortofon SPU.

Very good sound indeed, good dynamic and musical.

But the rest has been keeping like trash until now.

(Maybe) because many reasons that hard to bring them to life.

It is too high power (100W)/ It has 100V line output (not 16/8/4 ohm)/ It's heavy 😆/

It's using expensive power tube (2 of EL156)/ I'm too lazy (maybe the main reason 😁)

So I plan to re-design circuit, make it can exchangeable between EL12 & EL156.

Bypass microphone amplifier stage also tone control stage too.

Change to fully balanced circuit with input transformer and 1 high gain tube driver stage.

And finally using switching power supply instead of all parts in rectifier stage.

It will get about 20W output power, enough for me & my friend's speakers.

Let's see in next chapter but check the original before doing anything below.

Inside with German built... (from 1950's)

Many parts need custom to fit with standard components but interesting to make it possible.


Tuesday, December 22, 2020

Inside Northern Electric R4389B Theatre Bay

Last year my friend bought this "Northern Electric" mono theater rack sound system 

from local seller and ask me to restore to working condition.

Problem was information for this brand is hard to find, not like Western Electric equipment

that you can find from many sources.

After find out for long time, I can collect schematics that refer to each amplifier in the rack.

Then I thought to cluster them in my blog.

If someone want information should spend less time than me. 

Front side


Inside of back side for replace tubes (after restore).

Close up

R7877B Control Panel

R4137B Monitor Amplifier

Single 6V6 with input & output transformers and 6X5 rectifier tube.

Also has 4 ohm winding to connect monitor speaker too.

Schematic for R4137A & R4137B.

R6EB Amplifier

Inside of R6EB.

R6EB schematic with Mic & Phono inputs.

Information for strapping input & output impedances.

R4136B Amplifier.

Can check bias for all signal tubes.

This model can use schematic of Altec 323B Amplifier.

R7879B Field Coil Power Supply.

Using large Selenium Bridge Diode.

Hope all of these photos and information can be useful for someone or many.