SE 6V6 cathode resistor value - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

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
Reply
 
Thread Tools Search this Thread
Old 23rd May 2009, 12:47 AM   #1
diyAudio Member
 
Join Date: Jan 2009
Question SE 6V6 cathode resistor value

Me again. Still looking into a nice SE amp to build. I was planning a 6V6 powered model for a while...sort of a mutated Fender Champ with an extra gain stage and MV. While looking through some schematics I noticed that Fender used a 470 ohm cathode resistor on all of thier SE Champs, while the VM amp I have...also SE 6V6 uses a 300 ohm. Quite a difference, not? They both run the plate at about 350V and use a single 12AX7 in the preamp. Why such a difference in cathode resistors? The VM is from an old reel to reel player and is way more gainy than the Champ ( is gainy even a word ? I guess it is now !!)
  Reply With Quote
Old 23rd May 2009, 01:49 PM   #2
flysig is offline flysig  United States
diyAudio Member
 
Join Date: Apr 2009
A quick look at the 6V6 datasheet shows about 74mA of anode current, which through a 300 ohm resistor gives you a grid bias of -22v. That looks about right for a typical class AB1 push pull guitar amp. Going to the higher resistor would take it to seemingly too much bias of around -34v. At that much bias it is in cutoff and the amp won't be class AB1.

The answer is probably that it is a hi-fi design vs a guitar design.
  Reply With Quote
Old 23rd May 2009, 03:21 PM   #3
Funker is offline Funker  Germany
diyAudio Member
 
Join Date: Feb 2009
Location: Hamburg, Germany
Hi flysig,

refer to the Fender champ schematic . They use a high supply voltage of about 360V for the Champ. This operation point is not given in the tube data sheet. See link below!

http://tubedata.tigahost.com/tubedat...155/6/6V6G.pdf

The original Fender diagram show you a 470 Ohm kathode resistor. the kath. Voltage is 19V and resulting 40mA kath. current . The data specs of the 6V6 says max. Plate dissipation 12W and with 40mA you will be close to the limit. Assume 4mA for the screen left 36 mA Plate current. The Plate voltage is 350V and 19V at the kath . So the Plate turn 11,9W into heat.

To run a SE Amp with 70mA Plate current at abt 330V between Plate / kath dissipate 23 W and ruin the tube in few minutes . The 70mA in the data specs is valid for a PP amp with 2 tubes !

In my little homebrew amp there is also a 6V6 in the final. I run it with 420V supply voltage . 420 minus 30V at the opt winding and another 30Volts at the kath resistor give 32mA Plate current . The kath. resister is 910 Ohms .

If I would need much more current I should use a 6L6 in the final.


To find out which kath resistor sounds best. Replace the kath resistor against a potmeter in series with the low limit value resistor to avoid tube overload. Play the amp and adjust to the best sounding setting. By the way , SE audio amps can only run in class A.

regards from Hamburg
Wolfgang
__________________
Ground your devices before they ground you
  Reply With Quote
Old 23rd May 2009, 06:38 PM   #4
diyAudio Member
 
Join Date: Jan 2009
Thanks Flysig & Funker ( sounds like a law firm ...lol ). I am using the PT from the VM amp so I will try out the 300 ohm rK. I like the tone and the crunch of the VM so I have gutted a small SS combo to use the chassis and cabinet. My weekend project.
  Reply With Quote
Old 23rd May 2009, 07:40 PM   #5
diyAudio Member
 
dsavitsk's Avatar
 
Join Date: Jan 2005
Location: Hartford
This might prove helpful in answering your questions: http://boozhoundlabs.com/howto/
  Reply With Quote
Old 23rd May 2009, 09:39 PM   #6
flysig is offline flysig  United States
diyAudio Member
 
Join Date: Apr 2009
Quote:
Originally posted by Funker
Hi flysig,

refer to the Fender champ schematic . They use a high supply voltage of about 360V for the Champ. This operation point is not given in the tube data sheet. See link below!

http://tubedata.tigahost.com/tubedat...155/6/6V6G.pdf
Wolfgang,

Es tun mir leid! I missed that this is a single-ended design. Thank you for the link to tubedata, which is something that I desperately needed.
  Reply With Quote
Old 24th May 2009, 01:42 PM   #7
Funker is offline Funker  Germany
diyAudio Member
 
Join Date: Feb 2009
Location: Hamburg, Germany
Hi flysig,

after the first time you blow up your circuit design you enter the next level .

So here is my own design, I added a distortion stage to it . The Amp give 5 Watts. A friend of mine use it for rehearsal and small Pup gigs. The chassis and the enclosure is from a scraped chinese Trasistoramp which had a horrible sound.

Click the image to open in full size.

The Kath Resistor must be 910Ohms , in my drawing you see an 680 Ohm which is a wrong value The drawing was first for an 4 watter EL84 with 300V Supply . I used the same drawing and so I forget to change some values.

regards from Hamburg

Wolfgang
__________________
Ground your devices before they ground you
  Reply With Quote
Old 24th May 2009, 04:11 PM   #8
jjman is offline jjman  United States
diyAudio Member
 
Join Date: Jan 2009
The schematic for my '74 (Vibro) Champ shows 24v on the 470ohm cathode resistor and ~418v on the plate. That comes out to about 18watts

I changed it to a 750ohm and it idles around 12.5watts now.
  Reply With Quote

Reply


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
Replacing a cathode resistor with a CCS Original Burnedfingers Tubes / Valves 88 14th January 2014 06:36 PM
Help with CATHODE resistor value on 6BM8 PP Amp GlidingDutchman Tubes / Valves 3 18th June 2009 12:25 PM
Determining cathode resistor bereanbill Tubes / Valves 5 27th April 2009 11:33 PM
TVA-1 cathode resistor value audiohead Tubes / Valves 3 9th December 2007 07:15 PM
Wirewound cathode resistor Klimon Tubes / Valves 12 30th August 2006 10:19 PM


New To Site? Need Help?

All times are GMT. The time now is 08:03 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2