![\"\"](\"https:\/\/i0.wp.com\/www.bartola.co.uk\/valves\/wp-content\/uploads\/2017\/02\/C299-Mule-2.jpg\")
<\/a>I built the “Mule<\/a>” to provide enough flexibility to test other DHTs as pre-amplifier \/ line stage. Using the gyrator board<\/a>, the flexibility is fantastic. Can share same HT and dial the right anode voltage. The LT supply can also be shared amongst many DHTs and Rod Coleman provided me with a set of different resistors to test the list of 9 or 10 DHTs I have in mind which haven’t listed carefully on this design. <\/p>\nThe C-299<\/h2>\n
<\/p>\n
First one of the list is the rare 99\/199\/299.<\/a> This old DHT has thoriated filaments with low current and slightly less gain that the 01a. I push it hard to 4mA and beyond 90V. It can work well at 110-120V though. I want to minimise the slew-rate of the stage when driving the 4P1L PSE amplifier. 4mA is ok, if you’re worried you can bias it colder. I have a set of the C-299 as well as CX-299. Given I installed the UV-4 sockets, I added the C-299 with the socket adaptor.<\/p>\n They are slightly microphonic, but not much. I haven’t even starved the filaments. This hasn’t been a problem at all on my system.<\/p>\n The circuit is already popular, here we go:<\/p>\n The component selection is on the same lines as before. I have followed the advice from Barry French and trailing the Takman MF resistors on R5 and R7. The filament resistor is Kiwame. Russian caps, the rest is already known. <\/p>\n It measures really well. Great frequency response from 4Hz to 250kHz without loading the preamp:<\/p>\n The distortion is really low (lower than 0.002%) but didn’t save the measurement plot, next time.<\/p>\n The sound is very interesting. I can say after listening to a few records (including Giant Steps from Coltrane), the detail is very similar to the 01a. The bass is strong as it’s the detail of the treble. I like it, sadly has lower gain than the 01a. <\/p>\n Will listen to it for a while….<\/p>\n <\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" The start of a different DHT experience with the Mule I built the “Mule” to provide enough flexibility to test other DHTs as pre-amplifier \/ line stage. Using the gyrator board, the flexibility is fantastic. Can share same HT and dial the right anode voltage. The LT supply can also be shared amongst many DHTs … Continue reading “C-299\/CX-299 DHT Preamplifier”<\/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":[835,12,911],"tags":[853,216,632,1005,1006,1007,1008,186,47,44,888],"class_list":["post-6238","post","type-post","status-publish","format-standard","hentry","category-4p1l-pse-amp","category-dht-valves","category-gyrator-pcb","tag-01a-gyrator","tag-4p1l-pse","tag-bartola-valves","tag-c-199","tag-c-299","tag-cx-199","tag-cx-299","tag-dht-preamp","tag-dht-preamplifier","tag-gyrator","tag-gyrator-board"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-1CC","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/6238","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=6238"}],"version-history":[{"count":2,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/6238\/revisions"}],"predecessor-version":[{"id":6246,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/6238\/revisions\/6246"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=6238"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=6238"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=6238"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/i0.wp.com\/www.bartola.co.uk\/valves\/wp-content\/uploads\/2017\/02\/CX299-Preamp-V01.jpg?resize=751%2C730\")
<\/a><\/p>\nHow does it perform?<\/h2>\n
![\"\"](\"https:\/\/i0.wp.com\/www.bartola.co.uk\/valves\/wp-content\/uploads\/2017\/02\/cx299preamp-test01-1024x439.png?resize=525%2C225\")
<\/a><\/p>\n![\"\"](\"https:\/\/i0.wp.com\/www.bartola.co.uk\/valves\/wp-content\/uploads\/2017\/02\/C299-Mule-1-1024x688.jpg?resize=525%2C353\")
<\/a><\/p>\n![\"\"](\"https:\/\/i0.wp.com\/www.bartola.co.uk\/valves\/wp-content\/uploads\/2017\/02\/C299-Mule-3-1024x768.jpg?resize=525%2C394\")
<\/a><\/p>\nHow does it sound?<\/h2>\n