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
 23rd November 2005, 02:14 PM #1 dr._sleep   diyAudio Member   Join Date: Jul 2005 Location: southern us Loaded Question How does one calculate the load an input tube is working into when the next stage is a power tube, cap coupled? How about the Aikido input tube, its loaded by the other half of the tube? thanks, dr._sleep
jan.didden
diyAudio Member

Join Date: May 2002
Location: The great city of Turnhout, BE

Quote:
 Originally posted by dr._sleep How does one calculate the load an input tube is working into when the next stage is a power tube, cap coupled? How about the Aikido input tube, its loaded by the other half of the tube? thanks, dr._sleep

I assume you mean AC load (the DC load is different). Is the power tube into grid current? That is a load for the driver (or prestage). If not, you have - for AC - everything in parallel to make up the load: pre tube anode load, next stage grid resistor, whatever. Remember, for this calculation, for AC, the B+ and ground are the same, and the cap can be seen as a short. Any impedances to either B+ or ground, on either side of the cap, are in parallel.

Jan Didden
__________________
Music is dither to the brain; lets me think below the usual chaos - me
Get more Linear Audio for less! Check out my Autoranger and SilentSwitcher

Miles Prower
diyAudio Member

Join Date: May 2005
Location: USA
(See attached)

The load of the next stage grid is composted of the grid resistor in parallel with the specified capacitances: the grid-to-cathode capacitance, plus the Miller capacitance from: C(miller)= Cgp(1 + Av), plus the inevitable stray capacitance. The latter can be guesstimated as 30pF (you can't make it much less, but you can make it considerably more with poor construction techniques).

For the low frequency end of the audio range, the tube capacitances can be ignored. At the high frequency range, these become important and it is necessary for your driver to be able to supply those additional currents if you are to avoid slew rate distortion. If you don't go into grid current, then just about any medium u tube operated a sane load line should provide that current to any pentode or beam tetrode operated as pentodes/tetrodes. (High u tubes may not have enough moxie to drive a power tube directly, so you can use a cathode follower for adequate power grid drive.) This can possibly become problematic if triodes are used, as power triodes typically have larger Miller capacitances.

Of course, classes that require grid current have the additional load represented by the resulting grid current. In those cases, you probably need xfmr coupling or something like a power MOSFET to supply the necessary grid power. And that's a whole 'nother story.
Attached Images
 vt-input-ckt.gif (3.6 KB, 58 views)
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com

 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 munkittrick Car Audio 15 27th May 2009 12:49 PM gnugear Full Range 16 11th March 2008 10:24 PM BHD Full Range 13 13th December 2006 07:15 PM Bull Multi-Way 3 4th September 2005 09:55 AM zobsky Multi-Way 5 21st September 2004 08:13 PM

 New To Site? Need Help?

All times are GMT. The time now is 08:39 PM.