Input stage
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 10th May 2010, 09:52 PM #1 el156   diyAudio Member     Join Date: Apr 2010 Location: ALBUFEIRA ;PORTUGAL Input stage HI ! I have been spending lots of time to make the best input stage for my new amp! I want to use a 12AT7 (ECC81) ,and i need a plate voltage of 90V,because it is direct coupled with next tube (12B4A as phase splitter),and i want to have about -3v in the grid of the 12AT7, because i will use a CD player, an the output of it is about 2V. I have B+ of 280V! What value of plate resistor and cathode resistor should i use to get this values? And i would like to have plate current of about 3ma! Is this possible? Thanks
 10th May 2010, 10:02 PM #2 Globulator   diyAudio Member     Join Date: Aug 2004 Location: Cambridge, England. Check out this link: How to "Screw Around" Your Tube Load Line You can work out most stuff using Ohms law. An anode resistor at 3mA dropping (280-90) = 190V will be: R = V / I = 190/3E-3 = 63k Now for a plate voltage at 3mA on an ECC82 lookup the load lines and locate Ia = 3mA and Va = 90V, so we get a Vg = 1V. So to get 1V on the grid (actually -1V) you need a cathode resistor that gives 1V at 3mA, or R = 1/3E-3 = 330R. Job done.
 10th May 2010, 11:04 PM #3 hemgjord   diyAudio Member   Join Date: Apr 2007 Sorry to say but -3V and 90V is not gonna happen with ECC81, it is cut off. I would suggest a more "low voltage tube" like ECC88/6dj8 where you could achieve a reasonable working point at -2 to -2,5 V on the grid with 90V on the plate. /Olof __________________ I'm not allowed to do magic, union rules...
el156
diyAudio Member

Join Date: Apr 2010
Location: ALBUFEIRA ;PORTUGAL
Input stage

Quote:
 Originally Posted by hemgjord Sorry to say but -3V and 90V is not gonna happen with ECC81, it is cut off. I would suggest a more "low voltage tube" like ECC88/6dj8 where you could achieve a reasonable working point at -2 to -2,5 V on the grid with 90V on the plate. /Olof
THANKS, that makes sense, but i need a higher gain tube for this input and working in class A all the time and no more than 90V on plate ! any suggestions?
Thanks

 11th May 2010, 10:31 AM #5 Globulator   diyAudio Member     Join Date: Aug 2004 Location: Cambridge, England. Use my post to calculate the operating point of an ECC88 - you just need the ECC88 load lines - google 'ECC88 datasheet'. The ECC88 has higher gain than the ECC81 I think - by quite a bit. ETA: Looked it up - you need -2.8V grid for 3mA at 90V, Rk = 2.8/3e-3 = 933 Ohms, pick 910R. Last edited by Globulator; 11th May 2010 at 10:35 AM.
el156
diyAudio Member

Join Date: Apr 2010
Location: ALBUFEIRA ;PORTUGAL
Quote:
 Originally Posted by Globulator Use my post to calculate the operating point of an ECC88 - you just need the ECC88 load lines - google 'ECC88 datasheet'. The ECC88 has higher gain than the ECC81 I think - by quite a bit. ETA: Looked it up - you need -2.8V grid for 3mA at 90V, Rk = 2.8/3e-3 = 933 Ohms, pick 910R.
Thanks Globulator!
I will make a few tests later on with ECC88, probably it is the best choice i have to do what i want! i will post the results! I was looking inside an AUDIBLE ILLUSIONS preamp, and they use ECC88 with parallel triodes with 22K to anodes
and 510R cathode to ground with 800mf parallel !
Thanks

 11th May 2010, 01:40 PM #7 SY   On Hiatus     Join Date: Oct 2002 Location: Chicagoland Your other choice if you want to use an ECC81/12AT7 is to increase the plate voltage to accommodate the bias (2mA, BTW, is a good current for linearity) and then use a step network to couple to the next stage. __________________ "You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
SY
On Hiatus

Join Date: Oct 2002
Location: Chicagoland
Quote:
 Originally Posted by Globulator The ECC88 has higher gain than the ECC81 I think - by quite a bit.
Other way around.

Problem with ECC88 is that you want to run fairly high currents to get decent linearity. 5mA minimum, 8-10 is better.
__________________
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."

el156
diyAudio Member

Join Date: Apr 2010
Location: ALBUFEIRA ;PORTUGAL
Quote:
 Originally Posted by SY Other way around. Problem with ECC88 is that you want to run fairly high currents to get decent linearity. 5mA minimum, 8-10 is better.
Hi !
Yes,i would like to run ECC88 with higher current (about 5ma), but with grid bias
of about -3V ! How can i do that with Vb 280V and tha plate voltage cannot be more than 90V!Must i lower the Vb?
Thanks

 11th May 2010, 02:39 PM #10 Allen Wright   R.I.P.   Join Date: Dec 2001 Location: Schaffhausen Switzerland Do not worry about that 90V anode V rating. I have run them safely for years with 150 anode V's, and none less than Tektronix have used even high voltages on them to military reliability. Go for it! Regards, Allen

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post AudioGeek Tubes / Valves 2 20th March 2010 02:38 AM mahleriana Tubes / Valves 0 16th November 2009 10:37 PM maudio Solid State 15 11th October 2006 03:16 AM YUTK Solid State 11 2nd June 2005 04:34 AM

 New To Site? Need Help?

All times are GMT. The time now is 01:00 PM.

 Home - Contact Us - Advertise - Rules - diyAudio Store - Sponsors - Privacy Statement - Terms of Service - Top - Opt-out policy

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.