{"id":301,"date":"2015-06-20T18:59:16","date_gmt":"2015-06-21T01:59:16","guid":{"rendered":"http:\/\/tubetime.us\/?p=301"},"modified":"2015-06-20T18:59:16","modified_gmt":"2015-06-21T01:59:16","slug":"vacuum-tube-op-amp-experiments","status":"publish","type":"post","link":"https:\/\/tubetime.us\/index.php\/2015\/06\/20\/vacuum-tube-op-amp-experiments\/","title":{"rendered":"Vacuum Tube Op Amp Experiments"},"content":{"rendered":"

At the electronics flea market I recently found something particularly interesting…
\n<\/a><\/p>\n

This is a vintage Philbrick K2-W vacuum tube operational amplifier<\/a>! Turns out they have quite the following<\/a>. Sadly the original 12AX7 tubes were gone–somewhere, someone probably has rare GAP\/R marked tubes in their guitar amplifier. I put in some generic replacements.<\/p>\n

I decided to build a little jig to try it out.
\n<\/a>
\nThis is based on the inverting amplifier schematic given in the K2-W datasheet I linked above. I added a simple linear power supply to generate the +\/-300V rails. If you build your own supply, be sure to add bleeder resistors so you don’t get a nasty surprise after you turn it off and try to work on it.<\/p>\n

After connecting a 10K series and 100K feedback resistor to the op-amp, I ran a 1KHz 5Vp-p square wave from my function generator into the circuit and saw this:
\n<\/a>
\nNeat! The top trace is the input and the bottom trace is the output. The bottom trace has a magnitude of 50Vp-p, as expected.<\/p>\n

It’s really interesting to see how the short paragraph of specifications at the bottom of the first page of the K2-W datasheet developed into the formal electrical characteristics tables you can see in more modern op-amp datasheets, like the 741.<\/p>\n","protected":false},"excerpt":{"rendered":"

At the electronics flea market I recently found something particularly interesting… This is a vintage Philbrick K2-W vacuum tube operational amplifier! Turns out they have quite the following. Sadly the original 12AX7 tubes were gone–somewhere, someone probably has rare GAP\/R marked tubes in their guitar amplifier. I put in some generic replacements. I decided to […]<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"jetpack_publicize_message":"","jetpack_is_tweetstorm":false,"jetpack_publicize_feature_enabled":true},"categories":[5],"tags":[],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p80Z1r-4R","_links":{"self":[{"href":"https:\/\/tubetime.us\/index.php\/wp-json\/wp\/v2\/posts\/301"}],"collection":[{"href":"https:\/\/tubetime.us\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tubetime.us\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tubetime.us\/index.php\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/tubetime.us\/index.php\/wp-json\/wp\/v2\/comments?post=301"}],"version-history":[{"count":1,"href":"https:\/\/tubetime.us\/index.php\/wp-json\/wp\/v2\/posts\/301\/revisions"}],"predecessor-version":[{"id":428,"href":"https:\/\/tubetime.us\/index.php\/wp-json\/wp\/v2\/posts\/301\/revisions\/428"}],"wp:attachment":[{"href":"https:\/\/tubetime.us\/index.php\/wp-json\/wp\/v2\/media?parent=301"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tubetime.us\/index.php\/wp-json\/wp\/v2\/categories?post=301"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tubetime.us\/index.php\/wp-json\/wp\/v2\/tags?post=301"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}