Preamp 6v6 grid leak resistor value? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs 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

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 30th August 2009, 03:20 AM   #1
jetbat is offline jetbat  United States
diyAudio Member
Join Date: Nov 2008
Location: Maryland
Default Preamp 6v6 grid leak resistor value?

Hi, I need some help with 6v6 grid leak resistor values for use in a preamp. I got the idea using the 6v6 as a preamp tube from this thread.

6V6 line preamp

With this he is using a 100k pot for the grid leak I think. I am not using a pot in that position so I need to figure out what I can use.

Right now I am using the tube with fixed bias (-20V) and it works fine.
(see picture 1)
Now I want to try it with cathode bias but I'm not sure on the proper value of the grid lead resistor. Picture 2 is what I am thinking of trying.

Also I must say this is for a guitar amp. That is why I have the bias cold so I get some compression and distortion.

Looking a the datasheet, I am not sure which value to use. (see picture 3) Should I use the 500k or the 2.2meg recommendation for the upper limit.

Attached Images
File Type: png Picture 14.png (3.8 KB, 141 views)
File Type: png Picture 15.png (3.7 KB, 135 views)
File Type: png Picture 16.png (144.8 KB, 132 views)
  Reply With Quote
Old 30th August 2009, 05:11 AM   #2
diyAudio Member
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
I would think 500K would be fine. Sometimes you have to be careful using higher value grid leaks,even when they are suggested on the datasheet,it sometimes depends on the tube.
  Reply With Quote
Old 30th August 2009, 08:09 AM   #3
diyAudio Member
Rod Coleman's Avatar
Join Date: Jul 2004
Location: Warwickshire UK
So long as you're using a cathode resistor of 150 ohms or more, you can theoretically go to the 2.2M limit. But if the 6V6 is old and gassy, you may get bias stability problems.

in a guitar amp, set the gridleak R in combination with the coupling cap! The Fender/Marshall approach is 22nF/630V cap and about 220K gridleak. you could use 22n and 470K or 100n/100K according to what you have in a junkbox. All else being equal, a LOW value of gridleak is better, to counter the gas problem. The low values of coupling cap are used in guitar amps to limit the rumbly bass (especially in overdrive channels).

If the 6V6 is connecting to the pickup though (bad idea, gain too low for guitar) you need 1M gridleaks, or the pickup sounds dull.
  Reply With Quote
Old 30th August 2009, 08:49 PM   #4
jetbat is offline jetbat  United States
diyAudio Member
Join Date: Nov 2008
Location: Maryland
Thanks for the replies.

There is a 12ax7 tube in front of the 6v6 to drive it, so there is plenty of gain. I'm using .047uf coupling caps between the 12ax7 stages and the 6v6. I put a .1uf (what I had laying in front of me at the time) before the 6v6 to isolate the negative bias from a volume pot that I am going to remove. The low end is pretty thick but it sounds good. I was going to try .022uf caps and see how that sounds. As for the grid leak, I'll try the 220k since that is already in there.
  Reply With Quote


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
When to use a grid leak resistor? bequerel Tubes / Valves 8 25th April 2009 01:09 AM
Changing grid leak bias preamp to cathode bias bereanbill Tubes / Valves 8 28th March 2009 05:26 PM
Value of grid-leak resistor hkoetz Tubes / Valves 4 11th January 2009 04:15 PM
Value of grid leak resistor Klimon Tubes / Valves 4 10th November 2006 04:40 PM
screen-plate resistor and grid leak resistor metebalci Tubes / Valves 4 26th February 2004 03:18 AM

New To Site? Need Help?

All times are GMT. The time now is 02:34 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2