EL84 driving EL84 SET with fixed bias

cotdt · 06:13 AM

I would like to make a(nother) low-powered EL84 amp.

Rationale:
-EL84 has just the mu we want to drive another EL84
-With the same tube, we get distortion cancellation under a specific bias and voltage setting
-It is a VERY linear tube, and distortion should be extremely low with a CCS load
-Can make a low powered speaker amp, preamp, headphone amp, or driver stage for a 300B, 845, GM70, etc.
-The GE and Sylvania EL84 sounds very similar to a 45 DHT, but has the advantages of indirect heating. The Russian and Chinese tubes won't give that DHT sound, unfortunately.

To accomplish these goals I will use a CCS loaded driver stage and fixed bias on the output EL84. One can use a 12V battery or an adjustable power supply to adjust bias current.

jerluwoo · 12:10 AM

5W EL84 drive EL84 SE

cotdt · 6th December 2012, 12:33 AM

Thanks for the link, but the schematics on that page are not showing up due to broken links.

cotdt · 6th December 2012, 12:38 AM

Two of my goals for this project are:
(1) to compare the typical cathode bias for EL84 versus fixed bias. I really like the idea of a 9V battery, but have never tried.
(2) to evaluate the sound quality of EL84 as driver compared to others I've used to drive EL84 in the past such as 6DJ8, 12A*7, 12BH7, 5687, etc.

Svein_B · 6th December 2012, 05:35 AM

Have a look also at Thorsten Loesch's "Legacy" amp with SV83/EL84 pentode mode driver for 300B.

http://community.fortunecity.ws/rive...cy/Legacy.html

--
SB

jpjindex · 10th January 2013, 11:29 AM

Quote:

Originally Posted by Svein_B

Have a look also at Thorsten Loesch's "Legacy" amp with SV83/EL84 pentode mode driver for 300B.

http://community.fortunecity.ws/rive...cy/Legacy.html

--
SB

Hi Sven

Regarding this Legacy you posted the problem is the power supply.
I'm interested to assembly a Legacy but with another Power Supply.

Do you have some hints to give me?

Thanks

Jones

enzoastro · 10th January 2013, 12:43 PM

I think from my tests that there are better drivers tha n the el84. I dont know if you'd get some cancelation using the same tube though?

tinitus · 10th January 2013, 01:19 PM

EL84 drive EL84 could be something you do for fun
though I guess there would be better ways to build EL84 amp

funny, but yesterday I thought about using EL84 in a QUAD II style amp using the new Amplimo trafos with cathode feedback winding

cotdt · 16th January 2013, 06:46 AM

I just drew this on a piece of paper. Can you guys look this over before I start building?

artosalo · 16th January 2013, 07:29 AM

Based on my tests with many triode connected pentodes with CCS loading I think that the first EL84 will work well with smaller anode current, say 10 mA.
It's linearity is improved if the grid resistor of second EL84 is increased.
The maximum recommended by Philips is 300 k.

6th December 2012, 12:01 AM	#1
cotdt diyAudio Member Join Date: Oct 2005	EL84 driving EL84 SET with fixed bias I would like to make a(nother) low-powered EL84 amp. Rationale: -EL84 has just the mu we want to drive another EL84 -With the same tube, we get distortion cancellation under a specific bias and voltage setting -It is a VERY linear tube, and distortion should be extremely low with a CCS load -Can make a low powered speaker amp, preamp, headphone amp, or driver stage for a 300B, 845, GM70, etc. -The GE and Sylvania EL84 sounds very similar to a 45 DHT, but has the advantages of indirect heating. The Russian and Chinese tubes won't give that DHT sound, unfortunately. To accomplish these goals I will use a CCS loaded driver stage and fixed bias on the output EL84. One can use a 12V battery or an adjustable power supply to adjust bias current. Last edited by cotdt; 17th January 2013 at 06:13 AM.

6th December 2012, 12:06 AM	#2
jerluwoo diyAudio Member Join Date: Feb 2006 Location: Ashland,Ky U.S	5W EL84 drive EL84 SE Last edited by jerluwoo; 6th December 2012 at 12:10 AM.

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6th December 2012, 12:33 AM	#3
cotdt diyAudio Member Join Date: Oct 2005	Thanks for the link, but the schematics on that page are not showing up due to broken links.

6th December 2012, 12:38 AM	#4
cotdt diyAudio Member Join Date: Oct 2005	Two of my goals for this project are: (1) to compare the typical cathode bias for EL84 versus fixed bias. I really like the idea of a 9V battery, but have never tried. (2) to evaluate the sound quality of EL84 as driver compared to others I've used to drive EL84 in the past such as 6DJ8, 12A*7, 12BH7, 5687, etc.

6th December 2012, 05:35 AM	#5
Svein_B diyAudio Member Join Date: Oct 2005	Have a look also at Thorsten Loesch's "Legacy" amp with SV83/EL84 pentode mode driver for 300B. http://community.fortunecity.ws/rive...cy/Legacy.html -- SB

10th January 2013, 12:43 PM	#7
enzoastro diyAudio Member Join Date: Oct 2010 Location: se england	I think from my tests that there are better drivers tha n the el84. I dont know if you'd get some cancelation using the same tube though?

10th January 2013, 01:19 PM	#8
tinitus diyAudio Moderator Join Date: Nov 2005	EL84 drive EL84 could be something you do for fun though I guess there would be better ways to build EL84 amp funny, but yesterday I thought about using EL84 in a QUAD II style amp using the new Amplimo trafos with cathode feedback winding

16th January 2013, 06:46 AM	#9
cotdt diyAudio Member Join Date: Oct 2005	I just drew this on a piece of paper. Can you guys look this over before I start building?

16th January 2013, 07:29 AM	#10
artosalo diyAudio Member Join Date: Feb 2010	Based on my tests with many triode connected pentodes with CCS loading I think that the first EL84 will work well with smaller anode current, say 10 mA. It's linearity is improved if the grid resistor of second EL84 is increased. The maximum recommended by Philips is 300 k.