SURFING MUSIC SOUND-WAVES

My  DREAM was  to build and own a DHT26 .  The #26  tube  is renowned to be "par excellence" sounding but the SO-MUCH notorious hum seems to deter most of DIY-ers . I took it up as the challenge and spend quite some time in selecting a appropriate design while collecting  parts . Kevin Kennedy / KTA 's design  filled  my heart . It took me 5 months tedious toiling and communicating intensely with Kevin to understand this "temperamental" #26  tube , but then  I have been able achieve  excellent success in overcoming  the hum. The reward is one of the  purest and most beautiful sound . Its fluidity , tonality and  harmonics is amazing . No wonder that Jim de Kort (www.vt52.com) in his homepage has dedicated a extensive article to this tube and labeled the  DHT26 as "the angel-voiced tube".....

 Progress Clipboard

 Separate chassis for Signal and Powersupply. Tube regulated Plate  Power supply and CCS for heater supply

 Some of the #26 tube variations I tried-out initially  in the  DHT 26 preamp:

                   Philco ST 26                                       Cunningham CX326                 RCA UX226          Victor ST 26

28 Feb 08  :

The DHT26 line-amplifier was fully finished on 28 February 2008 and external bench-marking done on 8 March 2008. Using a CCS (vers1) reduced substantially the hum.

 (Go to Constant Current Supply page for further information)

The  excellent but rare and vintage UTC A25 line-output transformer as output mode  made it a very low-gain animal, something like a crossbreed between a passive controller and a very low-gain power amplifier - but with  refined sonic !

My last step was the vintage front control knobs and a try-out at Arif's Place.

                  DHT26 as my newline-amplifier                                 Try-out at Tube-Lovers place, 08 March 2008       

  LOT : UTC  A25  15K : 500 Ohm / max 8 mA DC current                                                                

08March 2008 - A BIG THANK YOU  !!!! 

Kevin Kennedy / KTA for his DHT26 design and guidance.

 Setiawan , for  the mains transformer and  the  CCS .

 Mauri Pannari, Finland , for  additional guidance  to choosing a appropriate  line output transformer.

Arif Wicaksono - the "TubeLover" - sharing his precious mono-blocks ( with the exotic RS242 tubes !!) during the test-out  , other unnamed friends  for  sharing knowledge and experiences

13 March 2008 

Try-out on the 01A/112A and 201-301A tubes on the DHT26 with its slightly lower B+ The fierce glow of the 01a type tubes  is a  attractive sight.  I am  really a sucker....

 Upper Pic : The fierce glowing Cunningham ST 01a type tube

 Note 1 :

 The DHT26 was build with flexibility in mind to accept several tubes within its family through a user-selected (B+) anode voltage supply (90-150Vdc) and trimmable CCS heater supply ( 1-5Vdc)

The following DHT tubes can be "plugged & played"  with :

Type 26 (#226/#326), #30, #00 and #01a (#201/301/201a/301a) ,  #12a/112a, B406 

Note 2 :

Its Output-Mode was made flexible , a choice of either "output-capacitor" mode or "output-transformer" mode can be easily implemented. But after one gets hooked on a outputtransformer , he/wont be able to get away .....

 13 June 2009

The rare Vintage Phillips Miniwatt  DHT #B406  tube as another choice.

Tube anode specification resembles the DHT #112A tube  ( Va: 135Vdc/5mA)

Successful Test-drive Specs :

Vp 120Vdc / 5mA , Bias maintained at minus 9Vdc  ,   Vf 4Vdc/0.1mA , G = 6 , Ra = 6000 Ohm.

LOT used : made by  Electraprint/ USA -  15K/ 600 ohm / max 15mA primary DC current

 Slightly different sonic character   compared to the DHT 112A tube. Excellent -  sweeter sound than the 112A

Its character could be caused by the Electraprint LOT. Needs to compare further with the UTC A25

 Thanks to Jack Elliano,  Electraprint to customwound the transformer.

01 December 2009

 For a change , I have swapped the #112A tubes with the rare vintage Phillips B406. 

The LOT is back using the superior sounding  UTC A25 .

Electraprin  LOT will be used for the IDHT27 line-amp.

How about its sonic signature ?....

I won't say anything ...to me its a personal sonic preference.... Try it out !!!

But for the tube itself , its a amazing quality vintage production  from year 1925 ...

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Technical operational specs with B406:

B+ max 120Vdc

Bias minus 9 ,

Current 5mA