{"id":8388,"date":"2020-04-28T19:50:15","date_gmt":"2020-04-28T18:50:15","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=8388"},"modified":"2020-04-28T20:53:45","modified_gmt":"2020-04-28T19:53:45","slug":"300b-se-amp-build-part-ii","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2020\/04\/28\/300b-se-amp-build-part-ii\/","title":{"rendered":"300B SE Amp: build part II"},"content":{"rendered":"

Slowly making progress during the lockdown period. Over the past few weeks I managed to achieve quite more than I was expecting. The fixed bias and 300B filament supply board (board 1) needs to be wired. On the other hand, the driver filament supply plus the HT supply board is completed (board 2):<\/p>\n

\"\"<\/a>
Board No. 2: HT Supply and DHT driver filament supply<\/figcaption><\/figure>\n

I tested the HT supply and can deliver over 430V. It has more voltage capacity, however the filtering capacitors are 450VDC. \u00a0The DHT filament supplies can do 8V to 15V to accommodate different filament requirements (including some level of filament bias). It works beautifully!<\/p>\n

Last night I did a quick job to build a pair of source follower boards. They will drive the 300B grid with DC coupling. The whole fixed bias arrangement will be as follows:<\/p>\n

    \n
  1. Raw supplies for -200V and +25\/50V for positive grid current supply and correct operation of the pass-MOSFET in the follower<\/li>\n
  2. Swenson+ regulator for bias<\/li>\n
  3. Channel trimpot and coupling capacitor for independent channel bias setting. This will be in one PCB<\/li>\n
  4. Each channel has a source follower biased at 20mA<\/li>\n<\/ol>\n

    Here is a snapshot of the boards:<\/p>\n

    \"\"<\/a>As I ran out of these PCBs, I decided to make a minor upgrade on the boards before requesting a new batch. I added a series resistor and parallel LED for either A2 operation or normal operation indicator. Also place underneath the board to solder a film\/PIO 100nF decoupling capacitor as needed.<\/p>\n","protected":false},"excerpt":{"rendered":"

    Slowly making progress during the lockdown period. Over the past few weeks I managed to achieve quite more than I was expecting. The fixed bias and 300B filament supply board (board 1) needs to be wired. On the other hand, the driver filament supply plus the HT supply board is completed (board 2): I tested … Continue reading “300B SE Amp: build part II”<\/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":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[5],"tags":[610,836,544],"class_list":["post-8388","post","type-post","status-publish","format-standard","hentry","category-valves","tag-300b","tag-300b-amplifier","tag-300b-fixed-bias"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-2bi","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/8388","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=8388"}],"version-history":[{"count":2,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/8388\/revisions"}],"predecessor-version":[{"id":8392,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/8388\/revisions\/8392"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=8388"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=8388"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=8388"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}