{"id":6228,"date":"2017-02-11T13:18:54","date_gmt":"2017-02-11T13:18:54","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=6228"},"modified":"2017-02-11T13:21:52","modified_gmt":"2017-02-11T13:21:52","slug":"gyrator-fet-options-more","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2017\/02\/11\/gyrator-fet-options-more\/","title":{"rendered":"Gyrator FET options (More!)"},"content":{"rendered":"

Someone had to invest and sacrifice some gyrator boards<\/a> to test various lower FETs (either depletion or enhancement devices as well as TO-92 or SMD options). That was me. <\/p>\n

Why? Because I want to push this circuit further and find the best options as well as provide to the builders out there some other device alternatives when they can’t solder SMD components. <\/p>\n

So let me present you the abused test mule and the various boards under the mercy of my tests:<\/p>\n

<\/a>
Boards with different FETs under test<\/figcaption><\/figure>\n

So What FETs where analysed? Here is the list:<\/p>\n

    \n
  1. BSSH111BK<\/a>: N-Channel, Enhancement, 55V, 335mA, SMD device (needs to be mounted in 45 degrees or with an adaptor)<\/li>\n
  2. 2N7002<\/a>: N-Channel, Enhancement, 60V, 115mA, SMD device (needs to be mounted in 45 degrees or with an adaptor)<\/li>\n
  3. 2N7000<\/a>: N-Channel, Enhancement, 60V, 200mA, TO-92 – fits perfectly on the PCB board.<\/li>\n
  4. BS107A<\/a>: N-Channel, Enhancement, 250V, 250mA, TO-92 – fits perfectly on the PCB board.<\/li>\n
  5. BSS123<\/a>: N-Channel, Depletion, 100V, 150mA, SMD device (needs to be mounted in 45 degrees or with an adaptor) <\/li>\n<\/ol>\n

    The test circuit<\/h2>\n

    The test circuit is very simple. The classic DHT preamp stage with a 4P1L in filament bias. The HT supply is regulated 300V with a decoupling 100\u03bcF ASC Oil cap with a 100nF film cap in parallel. To separate FR impact from the load, the load is the test set in parallel with the 510k\u03a9 R8.  The following components differ between boards as am planning to use them in different circuit from the 4P1L but shouldn’t affect the results of the below tests:<\/p>\n

      \n
    1. R4: Either 300k\u03a9 or 390k\u03a9 (preferred for 4P1L)<\/li>\n
    2. C1:100nF and R6 10M\u03a9<\/li>\n
    3. R7: 300\u03a9 or 470\u03a9<\/li>\n
    4. Rf: 15\u03a9<\/li>\n<\/ol>\n

      All tests were conducted with If=650mA and the 4P1L biased to Ia=30mA\"\"<\/a><\/p>\n

      Below are the tests conducted.<\/p>\n

      \"\"<\/a>
      BSSH111BK test<\/figcaption><\/figure>\n
      \"\"<\/a>
      BS107a test<\/figcaption><\/figure>\n
      \"\"<\/a>
      BSS123 test<\/figcaption><\/figure>\n
      \"\"<\/a>
      2N7002 test<\/figcaption><\/figure>\n
      \"\"<\/a>
      2N7000 test<\/figcaption><\/figure>\n

      So in summary, here’s my doggy bag take:<\/p>\n