{"id":7273,"date":"2018-03-13T20:41:42","date_gmt":"2018-03-13T20:41:42","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=7273"},"modified":"2021-02-19T10:09:51","modified_gmt":"2021-02-19T10:09:51","slug":"gm-70-se-amplifier","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2018\/03\/13\/gm-70-se-amplifier\/","title":{"rendered":"GM-70 SE Amplifier"},"content":{"rendered":"

I keep getting requests about SE amp designs using the 6SF5 driver<\/a>. Here is what I have come up with for the 6SF5 driving the GM-70. With only one stage you can drive the GM-70 to full power and get 18W out of this lovely transmitting valve:<\/p>\n

\"\"<\/a>
GM70 SE Amp<\/figcaption><\/figure>\n

I don’t think the circuit needs explanation. The driver is described on the 6SF5 blog post. The grid of the GM-70 is properly driven by a source follower<\/a> which also provides the DC bias using a Rod Coleman regulator (or any other regulator) The output stage relies on the scary 1.1kV HT and also a very good quality 10K OPT<\/p>\n

This is not for beginners, so I g<\/p>\n

et somehow scared when people ask me how to calculate the loadline of this circuit!<\/p>\n

The Rod Coleman regulator is mandatory as no AC heating is viable here. Rod can help you with the LT supply design.<\/p>\n

Hope this helps and no one dies in the process of building this amp! You’ve been warned \ud83d\ude42<\/p>\n

You are not limited to the 6SF5 of course, you can use many other great triode (or pentode) drivers here. You just need to have enough headroom and gain to deliver effectively 200-220Vpp. Not many drivers can do this well at low distortion. If you don’t want to pursue the DHT route (e.g. an 801a\/VT-25 with a 1:8 SUT) you can look into D3a, E810F as well as many others I have blogged around here:<\/p>\n

\"\"<\/a>
GM-70 10K loadline example<\/figcaption><\/figure>\n

You can use any of these drivers as shown below. Instead of SiC diode bias if you prefer a good quality resistor (un-bypassed) will work perfectly well in the hybrid mu-follower topology:<\/p>\n

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

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

I keep getting requests about SE amp designs using the 6SF5 driver. Here is what I have come up with for the 6SF5 driving the GM-70. With only one stage you can drive the GM-70 to full power and get 18W out of this lovely transmitting valve:<\/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_feature_clip_id":0,"_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":[1123,746,759,1124,44,875,1062],"class_list":["post-7273","post","type-post","status-publish","format-standard","hentry","category-valves","tag-bartola-source-follower","tag-cree-c3d02060f-bias","tag-gm-70","tag-gm-70-se-amplifier","tag-gyrator","tag-gyrator-pcb","tag-source-follower-pcb"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-1Tj","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7273","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=7273"}],"version-history":[{"count":4,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7273\/revisions"}],"predecessor-version":[{"id":9280,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7273\/revisions\/9280"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=7273"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=7273"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=7273"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}