Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

Input Choke Too Small
Input Choke Too Small
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
Thread Tools Search this Thread
Old 29th September 2007, 10:07 PM   #1
dre7 is offline dre7  United States
diyAudio Member
Join Date: Jul 2004
Location: U.S.
Default Input Choke Too Small


First a big thanks for this forum and all the information I've been able to glean here. I've been trying to electrocute myself for a few years now and in the process have built a few nice amps and repaired some others. The inevitable result of all this tinkering is a garage full of parts. So my idea was to build a "junkbox amp" out of them. PP 6B4G/ transformer splitter/6J5 driver/input transformer. Just got through breadboarding and the PS threw me a loop. Everything went fine cranking up the variac until I got past 100vac or so then the voltage starting runaway. Before runaway, B+ was hovering around 340v, a bit higher than I wanted, but I believe still within the capabilities of the Sovtek monoplates I'm working with. It's choke input PS and I think what's going on is the choke is too small (4 Hy) and "disappearing" past critical voltage at which point my PS becomes cap input.

I know the best solution would be a larger choke, but there are cost and chassis space issues as well as a garage to clean! So in that spirit, is there anything to do?

My thought was a bleeder resistor at the end of the voltage rail, but how do I figure the amount of current to pull to keep the choke from saturating?

Thanks for any help. This is my first go at trying to design something.

Will also try to post schematic.
Attached Images
File Type: jpg testpp6b4g.jpg (30.4 KB, 216 views)
  Reply With Quote
Old 29th September 2007, 10:35 PM   #2
Eli Duttman is online now Eli Duttman  United States
diyAudio Member
Join Date: Apr 2004
Location: Monroe Township, NJ
A reasonable approximation for the critical current (in mA.) is given by V/L. It works out that a 4 KOhm bleeder resistor is what's needed with a 4 H. 1st inductor.

If you use filter caps. that would survive under cap. I/P conditions, you can increase the value of the bleeder resistor and allow signal circuitry draw to complete entry into the choke I/P regime. Slow starting rectification, like that provided by 5AR4s and damper diodes, is your friend. The signal tubes will be hot and ready to conduct by the time B+ rise occurs. That allows the WVDC of the filter caps. to be held down. Subtract the idle current of the signal tubes from the critical current. Use Ohm's Law to compute the value of the bleeder resistor needed. Round down to the nearest "standard" value.
Eli D.
  Reply With Quote


Input Choke Too SmallHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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 Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Help for choke input regulated PSU inertial Power Supplies 5 1st September 2008 07:05 PM
Choke rating for choke input duty cbutterworth Tubes / Valves 14 9th November 2007 04:43 PM
Choke input PSU, drawbacks? dsavitsk Tubes / Valves 12 4th May 2007 11:52 PM
SOZ Choke input filter? gnomus Pass Labs 48 14th May 2004 06:41 PM
Resistor-Input vs. Choke-Input vs. Cap.Multip. Blitz Pass Labs 13 26th September 2003 04:59 AM

New To Site? Need Help?

All times are GMT. The time now is 05:50 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio