{"id":7825,"date":"2019-03-24T09:27:53","date_gmt":"2019-03-24T09:27:53","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=7825"},"modified":"2019-03-24T09:27:53","modified_gmt":"2019-03-24T09:27:53","slug":"eml20a-driving-eml45b","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2019\/03\/24\/eml20a-driving-eml45b\/","title":{"rendered":"EML20A driving EML45B"},"content":{"rendered":"

I’ve got asked the question on how an EML20 (or EML30)<\/a> can drive an EML45B<\/a>. Answer is straight forward and hopefully this brief blog entry can shed some light to this request.<\/p>\n

I recently looked back again on the EML20A<\/a>. With a gain of 20, it’s a good candidate but it hasn’t got just enough gain to drive the output stage to full power:<\/p>\n

\"\"<\/a>
EML45B with 5K OPT<\/figcaption><\/figure>\n

As you can see on the curves above, the 45B needs 176Vpp to produce about 4.6W. You can push it up to \u00a06W in class A2 with 200Vpp input signal. I’m not sure how the Emission Labs grid will work with positive grid current so I wouldn’t try this without checking with the manufacturer.<\/p>\n

With a 2Vrms input signal you will get about 113Vpp at the output of the EML20A. Not enough for full power and will give you 2W. You will need to add an extra input stage or a simple 1:2 SUT at the input.<\/p>\n

The EML20A has to be biased at higher voltage. Here is my suggested operating point:<\/p>\n

\"\"<\/a>
EML20A driver<\/figcaption><\/figure>\n

The EML20A has to be run at 300V at least. The EML30 is an alternative. I don’t know how linear and good this one is as I haven’t tried it myself. However looking at the curves you will need to run it at 400V at least. With the voltages involved and swing required, probably better to run it with choke load.<\/p>\n

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

As I’ve done it in the EML20A preamp circuit, the valve is biased with filament bias. The SiC diodes get hot, but can handle it. They drop close to 1.5V when running through large currents like in this circuit. So we will need 3 diodes to get about 4.5V. In this way we can allow 180Vpp swing. We may want to increase this to 5V bias and give some further headroom for 200Vpp or more. The HT is 410V and you notice as well that the negative raw bias supply has to be around -200V as the 45B needs -88V at its grid and you need at least 100V swing voltage (in both directions).<\/p>\n

I’m sure this would make a great sounding DHT amp with these 2 nice valves!<\/p>\n

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

I’ve got asked the question on how an EML20 (or EML30) can drive an EML45B. Answer is straight forward and hopefully this brief blog entry can shed some light to this request. I recently looked back again on the EML20A. With a gain of 20, it’s a good candidate but it hasn’t got just enough … Continue reading “EML20A driving EML45B”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_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}},"categories":[5],"tags":[920,1216,1096,1134,1215],"class_list":["post-7825","post","type-post","status-publish","format-standard","hentry","category-valves","tag-45-amplifier","tag-45-single-ended","tag-eml-spice-model","tag-eml20a","tag-eml45b"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-22d","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7825","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=7825"}],"version-history":[{"count":1,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7825\/revisions"}],"predecessor-version":[{"id":7829,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/7825\/revisions\/7829"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=7825"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=7825"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=7825"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}