{"id":500,"date":"2012-07-29T12:35:02","date_gmt":"2012-07-29T12:35:02","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=500"},"modified":"2012-07-29T12:37:41","modified_gmt":"2012-07-29T12:37:41","slug":"26-dht-preamp-with-ll2745-opt","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2012\/07\/29\/26-dht-preamp-with-ll2745-opt\/","title":{"rendered":"26 DHT preamp with LL2745 OPT"},"content":{"rendered":"

Today I managed to finally test the Lundahl LL2745\/8mA specially designed by Lundahl for Thomas Mayer<\/a> for a 26\/01a preamp \/ line stage.<\/p>\n

The circuit tested is here<\/a>.<\/p>\n

Initially did some tests with fixed bias, normal DC heater supply from my workbench and HT from a passive capacitor multiplier also available in my workbench. Circuit breadboarded has long cables and we shouldn’t expect good 50\/100Hz noise levels as have many transformers and things around \ud83d\ude42<\/p>\n

Test 1: fixed bias<\/h1>\n
    \n
  1. Vgk=-6,8V<\/li>\n
  2. Ia=6mA, Va= 119V<\/li>\n
  3. THD=0.033% @ Vo=1.4Vrms<\/li>\n<\/ol>\n

    \"\"<\/a><\/p>\n

    ;<\/p>\n

    Test 2: fixed bias with Rod Coleman regulator<\/h1>\n
      \n
    1. Vgk=-6,8V<\/li>\n
    2. Ia=6.5mA, Va= 119V<\/li>\n
    3. THD=0.031% @ Vo=1.4Vrms<\/li>\n
    4. Vf=1.4V (minor starvation)<\/li>\n<\/ol>\n

      \"\"<\/a><\/p>\n

      Test 3: Filament bias with Rod Coleman regulator<\/h1>\n
        \n
      1. Vgk=-6,3V<\/li>\n
      2. Ia=6.5mA, Va= 119V<\/li>\n
      3. THD=0.031% @ Vo=1.4Vrms<\/li>\n
      4. Rfilament=5\u03a9, Vf=1.4V (minor starvation)<\/li>\n<\/ol>\n

        \"\"<\/a><\/p>\n

        As we shown earlier in other tests, filament starvation reduces THD slightly as expected. The OPT performs really well. Probably will look at starving a bit more filaments whilst doing a listening test<\/p>\n

        Will now proceed to rebuild the 26 DHT preamp with LL1660 with this circuit \ud83d\ude42<\/p>\n

        \"20120729-133737.jpg\"<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

        Today I managed to finally test the Lundahl LL2745\/8mA specially designed by Lundahl for Thomas Mayer for a 26\/01a preamp \/ line stage. The circuit tested is here. Initially did some tests with fixed bias, normal DC heater supply from my workbench and HT from a passive capacitor multiplier also available in my workbench. Circuit … Continue reading “26 DHT preamp with LL2745 OPT”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[1],"tags":[779,47,785,78,784],"class_list":["post-500","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-779","tag-dht-preamplifier","tag-ll2745","tag-rod-coleman-regulator","tag-thd"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-84","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/500","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/comments?post=500"}],"version-history":[{"count":3,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/500\/revisions"}],"predecessor-version":[{"id":506,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/500\/revisions\/506"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=500"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=500"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=500"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}