EL84 plate voltage.

mario13 · 2nd March 2011, 09:40 PM

Im bulding a guitar amp out of stuff I have layin around. I got it up and running and it sounds great but I have a few questions regarding my limit in plate voltage for my pp el84 power amp stage. The amp uses a 6SJ7 premap ala Fender Champ 5C1, a 12AX7 phase splitter (long tailed pair) and fixed bias. The way I've got it running I got 460v on the plates( from an RS 350-0-350v 150ma PT) but my negative bias is enough to keep me at sane idle plate disibation around 8W per tube. My screens are at about 350v. Is this pushing it or is it fine so long as my plate and screen current do not go over there max values(max disibation of plate and screens given a specific voltage).the amp is suprisingly loud and there is no redplating. I havent had the chance to scope the amp yet but this should deliver I think 20 watts plus power. Any thoughts or suggestions?
Thanx!
Mario.

vinylkid58 · 2nd March 2011, 10:10 PM

The 6BQ5 data sheet says max. 300/300v for screen and plate, but we all know this is being exceeded in all kinds of amps. If you're really worried, you could run 7189's instead, but they may not give you the same "tone". What EL84's are you running?

jeff

mario13 · 2nd March 2011, 10:21 PM

Hi Jeff,
I'm running Ediswan NOS 6BQ5's.

vinylkid58 · 2nd March 2011, 10:37 PM

They'll probably last longer than some of the new production EL84's. Wouldn't mind hearing the amp. Got any youtube clips?

jeff

SY · 2nd March 2011, 10:57 PM

IME, abusing the plate voltage rating of most EL84 doesn't pose as much of a hazard as exceeding screen ratings.

jjman · 2nd March 2011, 11:33 PM

Many guitar amps also violate the alleged max idle plate dissipation wattage for EL84s. Most use cathode bias. The schematic of my 1967 Harmony H415 idles at 299 (net) plate volts for around 12.7 watts each (including the screens.)

350-0-350 sounds too high to me as a starting point for el84s. But if it works..

2nd March 2011, 09:40 PM	#1
mario13 diyAudio Member Join Date: Jul 2010	EL84 plate voltage. Im bulding a guitar amp out of stuff I have layin around. I got it up and running and it sounds great but I have a few questions regarding my limit in plate voltage for my pp el84 power amp stage. The amp uses a 6SJ7 premap ala Fender Champ 5C1, a 12AX7 phase splitter (long tailed pair) and fixed bias. The way I've got it running I got 460v on the plates( from an RS 350-0-350v 150ma PT) but my negative bias is enough to keep me at sane idle plate disibation around 8W per tube. My screens are at about 350v. Is this pushing it or is it fine so long as my plate and screen current do not go over there max values(max disibation of plate and screens given a specific voltage).the amp is suprisingly loud and there is no redplating. I havent had the chance to scope the amp yet but this should deliver I think 20 watts plus power. Any thoughts or suggestions? Thanx! Mario.

2nd March 2011, 10:57 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	IME, abusing the plate voltage rating of most EL84 doesn't pose as much of a hazard as exceeding screen ratings. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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2nd March 2011, 10:10 PM	#2
vinylkid58 diyAudio Member Join Date: May 2005 Location: Victoria, B.C.	The 6BQ5 data sheet says max. 300/300v for screen and plate, but we all know this is being exceeded in all kinds of amps. If you're really worried, you could run 7189's instead, but they may not give you the same "tone". What EL84's are you running? jeff

2nd March 2011, 10:21 PM	#3
mario13 diyAudio Member Join Date: Jul 2010	Hi Jeff, I'm running Ediswan NOS 6BQ5's.

2nd March 2011, 10:37 PM	#4
vinylkid58 diyAudio Member Join Date: May 2005 Location: Victoria, B.C.	They'll probably last longer than some of the new production EL84's. Wouldn't mind hearing the amp. Got any youtube clips? jeff

2nd March 2011, 11:33 PM	#6
jjman diyAudio Member Join Date: Jan 2009	Many guitar amps also violate the alleged max idle plate dissipation wattage for EL84s. Most use cathode bias. The schematic of my 1967 Harmony H415 idles at 299 (net) plate volts for around 12.7 watts each (including the screens.) 350-0-350 sounds too high to me as a starting point for el84s. But if it works..

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