832 Transmitting Tetrode P-P Amplifier

 

 

 

 

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    I have a few cute 832 transmitting vacuum tubes keep inside my store-room for years, until recently a customer come to me and ask about 829 transmitting vacuum tube amplifier. He want an amplifier that similar power to 6BM8 in push pull, He is currently using Antique Sound Labs 6BM8 P-P amplifier but he want another set for his study room, with some kind of weird tubes. My suggestion is not to use 829, it can be too high power for him, around 40W Push-Pull at 600V of B+ power supply. I show him my 832 tube and he confirm with the 832 tube amp.

 

 

 

 

 

 

 

   I had search around on web and only found one design using 832, with 5670 driver in ultranalog page, After quick check on the schematic, I decided to design my own schematic to suit my customer's need. I choose 12AT7 as gain stage and phase splitter. My 832 is made in China, production date is 1960, which is 44 years old already. I wonder if it is still in good condition, I plug it in my tube tester and found that it's still working perfectly. I even increase to 300V of B+ power supply at 35mA without any problem.

  The B+ power supply is 250V and drawing 33mA per tube, and 200V for G2; running a bit cooler than the "coldwar" in ultranalog page. I use 320V for driver stage and experiments with lower supply, it works nicely so leave it for easier construction. I'm aiming for 5W of output, that should loud enough for a small room. The gain stage is directly coupled to PK phase splitter, and feed to 832, just another basic circuit. Output transformer is a pair of 8K  p-p transformer.      

  The wooden chassis is similar to 1626 Darling amplifier, actually those are left over from my 6c45pi projects. I build 12 pcs of these chassis for 6C45pi amplifier (6C45pi SPUD SE is the best selling amplifier, so far!) This chassis is last piece I have in-hand. Top panel is 3mm thick aluminium, after drilled, I spray it with epoxy under-coat, lightly sand it smooth then spray with flat black (#29). Aluminum can't take normal paint, but epoxy based paint works well.

  See the layout that I finished in an afternoon, look at the small blue LED indicator lamps at the center of tube socket, It light up the 832 tubes beautifully. The finished amp will clipping at 7 Watt RMS, and distortion is 1 % @ 5.8 Watt RMS.832 is not as linear as 6BM8, I apply small amount of feedback to reduce some distortion. Compare to the A. Sound Labs 6BM8 P-P, 832 have better sound stage and more dynamic. Now I have a real problem, My customer ask me to build another one and he ask me to sell off his 6BM8.:(

 

  Schematic can be download Here.

      Distortion curve at 1KHz, please click Here.

      Data sheet of 832 click here.

 

 

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