plate voltage and cathode resistor for octal outputs - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

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 25th April 2012, 02:56 PM   #1
diyAudio Member
Join Date: Jan 2004
Location: Minnesota
Default plate voltage and cathode resistor for octal outputs

I have seen 500ohms all the way to less than 300 ohms for class A SE outputs for the EL34,6550,6V6,6L6,5881, etc family.

I assume this question may have allready been asked, but for a standard output stage, what combo of plate voltage, output impedance, and cathode resistor would work for all the above?

Oh and include the 6W6 too.

This would be for a standard pentode output stage for guitar amp.

on a side note, is there a good tone control circuit that is low loss and single pot? thinking the moonlight tone control.

It is not you... you are it.
  Reply With Quote
Old 25th April 2012, 03:18 PM   #2
diyAudio Member
Osvaldo de Banfield's Avatar
Join Date: Dec 2011
Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
The cathode bias not only fixes the plate and screen current, also sets the maximum input voltage at the grids pin, so, increasing a bit the cathode bias ensures not grid current at a more high signal voltage. Check the manufacturer data sheet for the bias needed for each tube in particular.

Osvaldo F. Zappacosta. Electronic Engineer UTN FRA from 2001.
Argentine Ham Radio LW1DSE since 1987.
  Reply With Quote
Old 25th April 2012, 04:00 PM   #3
diyAudio Member
Join Date: Jan 2004
Location: Minnesota
what i am looking for is 1 plate voltage, cathode resistor and output impedance that would work for all of those tubes, so i can swap them for different "sounds"
It is not you... you are it.
  Reply With Quote
Old 25th April 2012, 04:25 PM   #4
diyAudio Member
Tubelab_com's Avatar
Join Date: Jul 2005
Location: West Virginia panhandle
1 plate voltage, cathode resistor and output impedance that would work for all of those tubes.......Oh and include the 6W6 too.
The maximum screen voltage for the 6W6 is 150 volts. Unless you are looking at a screen voltage regulator the plate voltage can't be much over 150 volts. The 6550 won't "rock" on 150 won't even sing the blues, but it might cry or wimper a bit.

You want a "one amplifier for every tube" deal? Use one of those Edcor "tinker box" power transformers that have multiple output taps so that you can switch between different B+ voltages. You can even use a seperate transformer for heaters with a variac on the B+ transformer.

Use a switch with several cathode resistors, then use a 5 or 6K OPT with multiple output taps and a switch for the speaker to the 4, 8 or 16 ohm taps.

I used to build "Turbo Champs" with additional switches for tube or SS rectifiers, different cathode bypass capacitors, triode or pentode connection, and switchable feedback.

These techniques can be used to extract the widest range of tones from each tube, but the user has to understand the limits of each combination.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
  Reply With Quote
Old 25th April 2012, 04:49 PM   #5
diyAudio Member
doozerdave's Avatar
Join Date: Feb 2012
Location: Kitchener, Ontario
You need to consider the screen voltage. Screen grid voltage dictates your idle current flow from plate to cathode. You then use your cathode resistor to set the control grid DC offset (idle bias). So for different B+ and different screen voltages (in different amps, let's say) you will likely come across different cathode bias resistor values and wattage.

I'm currently designing (well, it's designed, just needs to be started) a high voltage (500V B+) SE pentode so I'm in this zone.
  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
Summing two amplifier outputs with just a resistor perfknee Solid State 9 9th October 2011 04:51 AM
Plate Current VS Plate Voltage Graphs Captn Dave Tubes / Valves 2 13th February 2009 08:57 PM
How can I calculate voltage over cathode resistor? Nordic Tubes / Valves 27 30th April 2008 10:44 AM
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 05:58 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