{"id":7580,"date":"2018-09-09T15:43:52","date_gmt":"2018-09-09T14:43:52","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=7580"},"modified":"2018-09-09T15:43:52","modified_gmt":"2018-09-09T14:43:52","slug":"300b-amps-an-early-breadboard","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2018\/09\/09\/300b-amps-an-early-breadboard\/","title":{"rendered":"300B Amps: an early breadboard"},"content":{"rendered":"

Browsing my schematic archive I found this early implementation from some years ago on the 300B:<\/p>\n

\"\"<\/a>The amp design is straight forward. Let’s start from the output stage. The 300B is run hot at 33W (376V\/90mA) with a fixed bias of about -78V. I used a pair of LL1623\/90mA OPTs which I had wired on 3K:8 mode.<\/p>\n

The filaments are driven by Rod Coleman’s regulators which are floating and connecting one end of the filament (cathode) to ground. This leg goes via a current meter (A1) with a pair of protection diodes (D1 and D2). There is a timed fuse which I believe I ended up with a 150mA and not 200mA as shown in the diagram. Should the fuse blow, R2 will force the valve to nearly cut-off and protect the valve and OPT.<\/p>\n

The bias was implemented with a very early prototype from Rod Coleman of his fixed-bias regulator. The regulator was feeding a current of about 24mA through a 3K3 wirewound resistor to generate the bias voltage. I used a 4-wire Kelvin film cap (aka “Morgan Jones’ cap”) to provide a clean bias to the 300B via the secondary of the IT transformer.<\/p>\n

The HT supply was properly “over sized” and you can see it here<\/a>.<\/p>\n

The driver was based around the 6e5p<\/a> in triode mode. I wrote quite a lot about this and her sister 6e6p-dr. Both are great drivers. In this case, I biased it up to over 4.2-4.7V using a stack of my favourite SiC diodes. The IT was LL1671.20mA configured to 1:1 ratio. I used an HV Shunt Regulator set to about 40mA. Each channel had its own shunt regulator.<\/p>\n

\"\"<\/a>To get full output power of 8W you will need 52Vrms (146Vpp)drive. Therefore the driver should have at least 200Vpp\/70Vrms capability as headroom is needed. The 6e5p will drive the stage nearly at maximum output level with a standard 2Vrms input. If you have a lower input source, you should look at a different driver like the ones discussed here<\/a>.<\/p>\n

Looking at this amplifier today, I’d probably change the input driver for a hybrid mu-follower (aka gyrator<\/a>) plus a source follower<\/a> instead of the IT. Also output transformer would be the Monolith Magnetics(Summit S-9<\/a>)\u00a0which are superior than the Lundahls.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Browsing my schematic archive I found this early implementation from some years ago on the 300B: The amp design is straight forward. Let’s start from the output stage. The 300B is run hot at 33W (376V\/90mA) with a fixed bias of about -78V. I used a pair of LL1623\/90mA OPTs which I had wired on … Continue reading “300B Amps: an early breadboard”<\/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":[673,911,154,158,5],"tags":[610,29,887,606,607,864,894,1123,401,44,1174,822,749,885,1061],"class_list":["post-7580","post","type-post","status-publish","format-standard","hentry","category-300b-amp","category-gyrator-pcb","category-output-stage","category-se-designs","category-valves","tag-300b","tag-6e5p","tag-6e5p-triode","tag-6e6p","tag-6e6p-dr-triode","tag-bartola-gyrator","tag-bartola-pcb","tag-bartola-source-follower","tag-fixed-bias","tag-gyrator","tag-rod-coleman-fixed-regulator","tag-se-amplifier","tag-sic-cathode-bias","tag-single-ended-amplifier","tag-source-follower"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-1Yg","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7580","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=7580"}],"version-history":[{"count":2,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7580\/revisions"}],"predecessor-version":[{"id":7585,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7580\/revisions\/7585"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=7580"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=7580"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=7580"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}