{"id":3673,"date":"2014-08-04T18:02:39","date_gmt":"2014-08-04T17:02:39","guid":{"rendered":"http:\/\/www.bartola.co.uk\/valves\/?p=3673"},"modified":"2014-08-05T21:12:05","modified_gmt":"2014-08-05T20:12:05","slug":"4p1l-with-screen-as-anode","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2014\/08\/04\/4p1l-with-screen-as-anode\/","title":{"rendered":"4P1L with screen as anode"},"content":{"rendered":"

A friend in DIYAudio came up with a great idea of using the 4P1L<\/a> in a different way for a pre-amp\/line stage. Given availability of IT and its gapped current, he suggested connecting the 4P1L differently. Instead of using the anode as the anode element, the screen is used as anode. The 4P1L screen has a maximum current of 10mA and\u00a0dissipation\u00a0should be within the 1.5W.<\/p>\n

The 4P1L curves in this mode<\/h2>\n

Let’s look at an initial transfer curve with Uak=100V:<\/p>\n

\"4P1L<\/a><\/p>\n

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I wired the 4P1L in the following way to allow tracing with the uTracer:<\/p>\n

\"4P1L<\/a>The connection is slightly different as the one suggested by Indra. If you are looking to implement filament bias, you will have to rearrange the anode and\u00a0suppressor\u00a0grid connection and expect a slight shift on the curves given the change in bias. Filaments are in series here, however is\u00a0preferred\u00a0to wire them in parallel when using this valve in filament bias as a smaller filament resistor will be required given there is twice the filament current when filaments are connected in parallel. This will help to keep the output resistance lower as the size of this resistor is smaller (remember it is reflected\u00a0multiplied\u00a0by\u00a0\u03bc+1 times.<\/p>\n

Now plotting the transfer curves in this mode:<\/p>\n

\"4P1L<\/a><\/p>\n

Don’t ask my why I didn’t proceed with the expected 4V step below -12V. It just happened that my brain did the wrong basic math when typing fast!<\/p>\n

Approximating an SPICE model for these curves we can see that it matches very well:<\/p>\n

\"4P1L<\/a><\/p>\n

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Some thoughts<\/h2>\n

\"points\"<\/a>If we have a tranformer gapped between 5 and 10mA then we can bias the 4P1L at 100-113V. The anode resistance will be between 2K9 and 3K7 approximately. \u00a0This is even less than half of what the 26 anode resistance is. In fact, the 4P1L in this mode has higher anode current and power capacity as well as three times of the transconductance. All in all, is a real winner on paper at least. Haven’t heard the 4P1L in this mode, but am sure it will sound really well after using 4P1L in pre-amps for many years.<\/p>\n

I’d probably aim to run it at 8mA if possible to reduce anode resistance and operate the 4P1L out of the knee.<\/p>\n

The Spice model<\/h2>\n

Here is my version f the SPICE model for you to play with, you can download the file from the link below.I’ve been a bit lazy and haven’t updated the capacitances. Also, we don’t have Cg1g2 (now Cg1a) and Cg2k (now Cak) in the datasheet. We can plug in the Cg1k which is about 8.5pF.<\/p>\n

\n
**** 4P1L SCREEN AS ANODE2 Composite DHT *****************************************\r\n * Created on 08\/04\/2014 16:39 using paint_kit.jar 2.9\r\n * Curves and model created by Ale Moglia \/ valves@bartola.co.uk\r\n * www.bartola.co.uk\/valves\r\n * Plate Curves image file: 4P1L Screen as Anode2.png\r\n * Data source link: www.bartola.co.uk\/valves\r\n *\r\n * Capacitances not updated !!!\r\n * RFIL is 4.45V\/330mA<\/pre>\n
*----------------------------------------------------------------------------------\r\n .SUBCKT DHT_4P1L_SCREEN 1 2 3 4 ; P G K1 K2\r\n + PARAMS: CCG=3P CGP=1.4P CCP=1.9P RFIL=13.6\r\n + MU=9.6 KG1=1545 KP=111.6 KVB=256.7 VCT=0.374 EX=1.43 RGI=2000\r\n * Vp_MAX=200 Ip_MAX=20 Vg_step=2 Vg_start=4 Vg_count=12\r\n * Rp=4000 Vg_ac=55 P_max=40 Vg_qui=-48 Vp_qui=300\r\n * X_MIN=108 Y_MIN=158 X_SIZE=416 Y_SIZE=490 FSZ_X=1128 FSZ_Y=758 XYGrid=false\r\n * showLoadLine=n showIp=y isDHT=y isPP=n isAsymPP=n showDissipLimit=y\r\n * showIg1=n gridLevel2=n isInputSnapped=n\r\n * XYProjections=n harmonicPlot=n harmonics=y\r\n *----------------------------------------------------------------------------------\r\n RFIL_LEFT 3 31 {RFIL\/4}\r\n RFIL_RIGHT 4 41 {RFIL\/4}\r\n RFIL_MIDDLE1 31 34 {RFIL\/4}\r\n RFIL_MIDDLE2 34 41 {RFIL\/4}\r\n E11 32 0 VALUE={V(1,31)\/KP*LOG(1+EXP(KP*(1\/MU+V(2,31)\/SQRT(KVB+V(1,31)*V(1,31)))))}\r\n E12 42 0 VALUE={V(1,41)\/KP*LOG(1+EXP(KP*(1\/MU+V(2,41)\/SQRT(KVB+V(1,41)*V(1,41)))))}\r\n RE11 32 0 1G\r\n RE12 42 0 1G\r\n G11 1 31 VALUE={(PWR(V(32),EX)+PWRS(V(32),EX))\/(2*KG1)}\r\n G12 1 41 VALUE={(PWR(V(42),EX)+PWRS(V(42),EX))\/(2*KG1)}\r\n RCP1 1 34 1G\r\n C1 2 34 {CCG} ; CATHODE-GRID\r\n C2 2 1 {CGP} ; GRID=PLATE\r\n C3 1 34 {CCP} ; CATHODE-PLATE\r\n D3 5 3 DX ; FOR GRID CURRENT\r\n D4 6 4 DX ; FOR GRID CURRENT\r\n RG1 2 5 {2*RGI} ; FOR GRID CURRENT\r\n RG2 2 6 {2*RGI} ; FOR GRID CURRENT\r\n .MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N)\r\n .ENDS\r\n *$<\/pre>\n<\/blockquote>\n
The model can be found here as a well: “4P1L Screen as anode SPICE model<\/a>“.<\/p>\n
 <\/p>\n","protected":false},"excerpt":{"rendered":"
A friend in DIYAudio came up with a great idea of using the 4P1L in a different way for a pre-amp\/line stage. Given availability of IT and its gapped current, he suggested connecting the 4P1L differently. Instead of using the anode as the anode element, the screen is used as anode. The 4P1L screen has … Continue reading “4P1L with screen as anode”<\/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":[12,156,24,5],"tags":[782,522,142,595,623,289],"class_list":["post-3673","post","type-post","status-publish","format-standard","hentry","category-dht-valves","category-pre-amplifier-valves","category-valve-curve-tracer","category-valves","tag-4p1l","tag-4p1l-curves","tag-4p1l-preamp","tag-4p1l-preamplifier","tag-4p1l-screen-as-anode","tag-4p1l-spice-model"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-Xf","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/3673","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=3673"}],"version-history":[{"count":4,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/3673\/revisions"}],"predecessor-version":[{"id":3690,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/3673\/revisions\/3690"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=3673"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=3673"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=3673"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}