An observation about EL84's & the complaints I've heard

[bluesbear]

I've been reading some old posts. I don't know why; just bored, I guess. One thing I've noticed over and over:  "I don't like EL84's because they're too harsh, or bright, or raspy, etc." The problem is they're screaming in pain! Everyone wants to run them at 340+ volts... because Vox did it that way. Well, Vox was wrong! I've even seen them run at 400 volts. If you really want to hear whet EL84's can sound like, try them at 300 volts; no more than about 10 watts. Smooth, warm, and creamy, like a violin. I have some recordings I did helping out a songwriter friend, Dave Mayne, with some homemade amps. The following is using a GA-8 with EL84's. The scematic is attached (I left out the tremolo). All fills and the second guitar lead is this amp. Dave did the first guitar lead with a 5F6a pre- through a BF Deluxe power section.

http://angelamplification.com/SomewhereAlongTheWay.m4a

For comparison, the next song was done with a 5C3 (6V6). Believe it or not, this was the first take!

http://angelamplification.com/FriendsOutIntheCountry.m4a

And, just for fun, I'm most proud of this one. No guitar leads at all! But I talked him into the leads and fills that are there. He didn't like the idea but luckily, he tried it anyway.

http://angelamplification.com/TakeMeLikeYouFindMe.m4a

Anyway. there you go. Don't assume EL84's are inherently tinny. That's the voltage NOT the tubes.
Dave

[Geezer]

Hey BB, I couldn't agree more!

The challenge is finding PT's with a low-volt secondary......everybody offers the 300v to 330v secondaries, which yield way too much B+ for the EL84's.

What do you use? (or anyone else, for that matter....where do you get good low voltage secondary PT's?)
I have a ton of old PT's, but most are 350v to 400v, and were running/abusing 2x6v6's & the like (old Bogen/RCA/Knight PA's & such)

G

[zendragon63]

+1. I tend to run my builds up to 15% lower than typical FMV specs as I personally like a little more relaxed sound.  My beef with the EL84 is that when pushed, some tubes can get mushy (maybe because the mu is as high as it is?) while others stay more articulate.

Hammond does make a 250-0250 and used to made a 225-0-225 but IIRC both delivered less than 100ma. Good observation and advice. Thanks, Regards

dennis

[samato]

I find this very interesting.  That must be what I don't like about my Fender Pro Jr.  Very harsh.  I don't know off hand but they must have the el84's in that amp running at a pretty high voltage.  Can I do anything short of getting a new PT to safely lower the voltage to them?

Seems like 6V6's actually like the higher voltage though.  I have some running at around 460v in an AB763 circuit and they sound good.  Might be damaging them, not sure.  I also have nothing to compare to because I haven't tried running them lower.  My understanding is that if I do I'll lose clean headroom, which I don't want.

[JayB]

Yeah, much more than 300vdc and they get ice picky and just sound like garbage. 300vdc is the highest I would go and they sound great.

[pullshocks]

Well there's the Weber multi-tap PT https://taweber.powweb.com/store/PTGPsch.jpg

[Fresh_Start]

What about those Antek torroid PTs?

Chip

[samato]

Yeah, much more than 300vdc and they get ice picky and just sound like garbage. 300vdc is the highest I would go and they sound great.

So how do you do that?  Can it be done with resistors or something?  I don't want to install a new PT.

[tubenit]

I first built the HoSo56 with EL84's and had around 297v on the plates.

It sounded "OK". But it's just not the tone I like. I hear a chimey tone even at moderate voltages. I rewired the EL84's to
6BM8 which I prefer.

Having said that, I've heard people play EL84 amps and what I heard sounded absolutely great. And guys like Geezer who plays better then I will ever be able to play ........ likes them. And I like his playing and tone ALOT.

It's strictly a preference thing. I don't think EL84's are a "bad" tube.

With respect, Tubenit

[Dave]

I'd like a little more clarification on what we are talking about. My guess is that we're saying that EL84's don't sound very good if you run them at a voltage higher than X and you are running them hard enough to make them overdrive.

Is that what we are talking about? The overdriven sound of EL84's at voltage X or higher?

If so, what about the clean? There are several manufacturers out there making EL84 amps that have 400+ plate volts and are fixed biased. Rumor has it that they sound pretty good clean. I am fiddling with a customer's Carvin Nomad. It reads about 440 on the plates and the clean sounds pretty good to me. He hates the distortion. The distortion he hates is all happening well before the power amp anyway.

Interesting thread.

Dave

[tubenit]

Just to demonstrate how much I'm off in not loving EL84's................   

Here is an EL84 soundclip that to me is waaaayyy over the top cool.  I love that tone.

http://www.soundclick.com/bands/page_songInfo.cfm?bandID=1106945&songID=10333523&showPlayer=true

With respect, Tubenit

[samato]

Just to demonstrate how much I'm off in not loving EL84's................  

Here is an EL84 soundclip that to me is waaaayyy over the top cool.  I love that tone.

http://www.soundclick.com/bands/page_songInfo.cfm?bandID=1106945&songID=10333523&showPlayer=true

With respect, Tubenit

Oh, I don't mean to say I don't like the sound of el84's at all.  I just find that, at least in my Pro Jr., they get very harsh & ice-picky - mostly at high volume (playing with a drummer).

Still, I've gotten sounds I like with that setup.  I'm not sure if this link will work but here's my stock MIM tele through the stock Pro Jr. (Crybaby wah, Jekyl & Hyde OD/Dist. I think):

http://www.soundclick.com/player/single_player.cfm?songid=9540701&q=hi&newref=1

This sound isn't as harsh as it gets sometimes because the guy playing drums on this one had good dynamics.  Unfortunately most of the drummers I normally play with don't have his sensibilities.  That figures because he's a keyboard player, not a drummer - according to him!

By the way, the sound in your clip was indeed very cool!

[RicharD]

I like 6BQ5 amps wired cathode bias but w/o a cathode bypass cap.  Seems to kill the harsh sizzle.

[mcrracer]

Hey Bluesbear, On V1a is that 1M resistor connected to pin 5?

[bluesbear]

"On V1a is that 1M resistor connected to pin 5?"

Yes, but remember this is a 6EU7. Different pinout from a 12AX7. I had a hard time understanding that resaistor! I believe it's a local negative feedback loop. I left it out with no ill effects.
Dave

[bmack]

Yes, this week I had the same revelation with el 84's.  I just built a Watkins Dominator circuit using the chassis and iron from an old turntable console that ran el 84's.  Due to the power transformer  primary being rated at 115 and my wall voltage being 127, the plates were up around 355 volts.  The amp sounded good but was in your face as soon as you cracked the volume knob and that is about the only tone it got.
Using a variac I brought the AC voltage down to 112 which put the plates right at 300 volts- even lower than the 325 that the Watkins schematic specified.  There were so many more tones available running it like this.   Now I could get some chewy, vowel like sounds at lower volumes and still get that chimey grind if I want by turning the volume up higher.
 
To bring the voltage down on this build I'm going to use a vintage voltage adapter that R.G. Keen  discusses at his site ( although I believe it has been discussed here also).  I like this amp so much I'm planning to build another from scratch and also noticed that there aren't many choices for  P.T.'s with secondaries that deliver the proper voltages.  The hammond's I found that were 275-0-275 were rated for 115v which brings the secondary voltage right back up.  I think Edcor has a couple options in this range, I have to check again.  I'd be curious if anyone used an Antek toroid also.  Those seem like such a good deal. 

[mcrracer]

"On V1a is that 1M resistor connected to pin 5?"

Yes, but remember this is a 6EU7. Different pinout from a 12AX7. I had a hard time understanding that resaistor! I believe it's a local negative feedback loop. I left it out with no ill effects.
Dave

Thanks Bluesbear. Yeah I know the pinouts are different. I think I will have to add this one to "The List"!

[dude]

Anyone against lowering the voltage with Zeners?

I've used two 15 watt zeners in series to lower the voltage 30 volts, they do get hot but if you leave the leads long and don't use heat shrink tape they hold up well. Stand-offs work well.

Any thoughts whether to run them off the Pt's center tap to ground or in the B+ line?

al

[Baguette]

I hear you Bluesbear,
Just finished an 18W thingie with 290V B+ and 280V on the plates. It's crazy loud and dynamic, and much smotther than the average Vox when cranked up.

[phsyconoodler]

I do not agree.I built an 18 watt with a reclaimed PT that put 420v on the plates.After some tweaking to get the current and screens safe,it's the best EL84 tone of any I've done to date.

[samato]

Maybe it's a question of whether you're going for a high gain or a clean sound?  To me the Pro Jr. sounds good dirty or driven hard, though ice-picky at times.  The clean sound I get from it is too harsh or too "in your face" in most cases.  I don't know if this is characteristic of el84's or just this amp but that's what got me looking into 6V6's; a great clean sound is my priority.

[John]

Mine is running around 360 if I remember right, and honestly I think it sounds great. I remember not being able to match the R values exactly coming off the preamp tubes, and so maybe that contributes to the overall sound as well? I normally never go past halfway on the volume, and use some pedals for the overdriven sound at low practice volumes. Mine doesn't get really gainy till around 7 or 8 on the volume knob.

I'd have to look to be sure of the value, but the cathode R is higher than called for on the schematic; it's how I got the dissipation down to safe levels (still remember HBP saying that voltage doesn't kill tubes, current does).

Regardless, when I do  my first build, I'm sure I'll be using EL84s in it. I will try to get the B+ down around 300 though, just because I'd like to compare the sound.

Another thought: since the 84s are cheap, perhaps they're put into factory amps that are also cheaply built with little thought to tone? Could explain the crappy tone so many have attributed to them?

[RicharD]

"On V1a is that 1M resistor connected to pin 5?"

Yes, but remember this is a 6EU7. Different pinout from a 12AX7. I had a hard time understanding that resaistor! I believe it's a local negative feedback loop. I left it out with no ill effects.
Dave

That 1M resistor is the difference between a plate follower and a grounded cathode amplifier stage.  Yes, it is a local negative feedback loop.  It sets the gain of the stage, Rfb/Rin or 1M/47k=21.  W/O that resistor, the gain of that stage is >50.  I come up with 57 if the B+ is 300V.  It also ups the f-3dB high from 35kHz to almost 1MHz.  Another benefit is it almost triples the input threshold from 1.3V to 3.4V.  That's a big deal if you have a string of stomp boxes in front of the amp.
(numbers crunched using TubeCad w/ B+ = 300V)

I'm curious about how you have the input jacks wired.  With 1 jack being used, you now have a 47k in parallel with the 470k which for all intents and purposes means you have a 47k grid leak.  That seems like almost a lot of loading on the guitar pickup.  I'm not dissing, I'm just curious why.  I never build 2 hole inputs, but when I have, I usually plagiarize a Fender.  Beyond not understanding the input, that looks like a really smooth 1st gain stage.

[kagliostro]

Vox on 1960 AC30 used also a 280v - 0 - 280v PT

http://www.el34world.com/charts/Schematics/files/Vox/ac301960.pdf

May be there was a reason ...............

Kagliostro

[phsyconoodler]

There are other factors that come into play here too.The preamp voltages have a lot to do with the breakup characteristics of the amp.Just making a statement that higher than 300v on the plates of EL84's is kind of silly.
  With no other changes on an 18 watt Marshall circuit,I agree that closer to 300v is the best sound.But if you make changes to accommodate higher plate voltages they can sound absolutely killer good.
  And not just for cleans.The overdrive on mine is quite good.It has more touch sensitivity and grunt.i also brought the preamp voltages down to normal 18 watt levels so I would muck too much with the way the preamp section works.
 

[Fresh_Start]

There are other factors that come into play here too.The preamp voltages have a lot to do with the breakup characteristics of the amp.Just making a statement that higher than 300v on the plates of EL84's is kind of silly.
  With no other changes on an 18 watt Marshall circuit,I agree that closer to 300v is the best sound.But if you make changes to accommodate higher plate voltages they can sound absolutely killer good.
  And not just for cleans.The overdrive on mine is quite good.It has more touch sensitivity and grunt.i also brought the preamp voltages down to normal 18 watt levels so I would muck too much with the way the preamp section works.

Knee bone's connected to the ... leg bone
Leg bone's connected to the ... ankle bone
Ankle bone's connected to the... you get the idea

Part of the tone question may be WHICH EL-84s are you using.  I just never had great love for the tone of my Blues Jr. until I found out what Ei EL-84s sounded like in it.  (JJs were muddy, EH lifeless, Sovtek harsh - just my opinions of course!)

Anyone against lowering the voltage with Zeners?

I've used two 15 watt zeners in series to lower the voltage 30 volts, they do get hot but if you leave the leads long and don't use heat shrink tape they hold up well. Stand-offs work well.

Any thoughts whether to run them off the Pt's center tap to ground or in the B+ line?

al

I'm not sure it matters where you put the zeners.  If you put them in the B+ line, you don't have to worry about grounding issues.  If you put one on the center tap, you can get a 50 watt beastie that bolts to the chassis as a heat sink.  Here's a data sheet:  http://www.nteinc.com/specs/5200to5299/pdf/nte5240a.pdf
You need the part ending in "K" to get cathode to case.  You must ground the reservoir cap on top of the zener along with the center tap.  How you ground the rest of the power amp is up to you. I've sucessfully used one of these on a center tap to drop 50 volts.

Cheers,

Chip

[RicharD]

What about stacking a pair of 0D3's instead of Zeners?

http://www.mif.pg.gda.pl/homepages/frank/sheets/141/g/GL874.pdf

[bluesbear]

Sorry, I try not to get too theoretical. I just know the amps (and tone) I like and the ones I don't. Every amp I've heard with EL-84's with 340v or more just doesn't sound good to me... and that includes Vox's. I never have, even back in the 60's. Don't get me wrong, I loved the Beatles, just not the guitar tone. Now, I know I haven't heard EVERY amp, even with 50 years of trying. There's probably plenty of exceptions to what I said. However, I stand by the fact that EL-84's work better and last longer at lower voltages. Obviously, the tone is subjective. That's the point. People that don't like EL-84's need to hear them at a lower voltage to really be able to decide. People who like them at higher voltages have plenty of choices, for listening, buying, or building. I'm not saying there's a right or wrong here, just that there's a choice.
Dave

[Milnoque]

I''ve got a Gibson GA-20 RVT that's probably used more than any amp I own. You can't make it sound harsh if you try. Not muddy either. I like it because it gets sweet at very low volume and stays sweet much of the way up. Great amp for what I do. Not the loudest 12 watter though. 6BQ5s can be very musical in my opinion.

[phsyconoodler]

Quote:"However, I stand by the fact that EL-84's work better and last longer at lower voltages."

Again,not really true.Traynor amps with EL84's have been using voltages in excess of 400v since they first came out and many still have the original tubes they came with.
  It really depends on the circuit,not the plate voltages. I am with you on Vox amps though.I really don't like them much.
If you lower the current and screen voltages the tubes see,they last a very,very long time.the voltage is not really a concern.
  a lower voltage can sound 'browner' in many EL84 equipped amps,but not necessarily better.

[sluckey]

There were plenty of quality hi-fi amps in the '60s based on the EL84. And they ran high B+. The old Fisher I had ran the plates at 420V. Nothing harsh sounding about it.

I have heard a lot of EL84 guitar amps that do sound harsh though. The Marshall 18w is one of my faves.

[jojokeo]

Revisiting an earlier comment & theorizing aloud, why are so many PTs produced w/ such high voltages for these tubes (seemingly purposely) going way above their ratings? Increasing gain for more headroom makes sense but increasing voltage w/ the same old 100k load resistor or having the lower "normal operating voltage" w/in the tube's spec w/ a lower resistor would both accomplish the same thing, no?

Another is that I thought the developement of an EL84 was originally for the European's ability to operate them at their common 220/240 wall voltages? Which is why in spec sheets their operating characteristics are listed at 250v w/ limiting values at 300v. If they were meant to be ran at 400+ volts wouldn't they have been designed to do so?

Another is that they were designed for hi-fi, TV & radio use not guitar amps. As it says in Mullard's spec sheet, "this valve makes available the higher peak powers and low distortion required for present day receivers and power amplifiers for home listening, and is of particular importance now that better quality reception is provided by the FM service in band II." Was there ever an intentionally designed tube perfected for guitar amp use (are we being too finicky here)? What about poor design, poor preamp, poor speaker, poor OT, etc...all contributing to bad tone?

I tend to agree that the tubes being operated w/in thier dissipation/current limitations seem to sound perfectly fine. Now are these named amplifiers operating at 400v+ using the same 120 or 130 ohm cathode resistors? This suggests that they're running at a higher Pd than designed for. Is it possible or maybe even likely for the bad sounding amps to be overbiased and running too extreme of thier limits? Is there any kind of connections here we can make?

At the end of the day the final result may or may not be to the 'beauty of the 6-string slinger".

[Dave]

I think that most of the "commercial" amps being produced with EL84 plate voltages well over 400VDC are all relying on their preamps to provide distortion and essentially trying to run the power tubes clean. Most of the complaints about the distortion characteristics in these amps are inappropriately blamed on the power tubes.
That said, when running them hard enough to saturate, I don't know what the characteristics of the EL84 are at X or Y plate voltage.
So, they may very well sound a lot better at 300vdc as opposed to 400vdc. But, saying "My Meso Thelioma sounds like crap because it uses EL84's" is making really big assumptions unless you have run its preamp through a different power amp to verify that it really has the most fantastic preamp possible and the dead cow noises are all coming from the EL84's.

Just my opinion, please don't violate my human rights.

Dave

[bluesbear]

Well, like I said, I'm not a theoretician. I only know I've never heard a higher voltage EL-84 amp I liked. Every lower voltage EL-84 amp I've heard , I've loved. I know many people, if not most, like the higher voltage amps. If someone has made them in a way that overcomes what I consider to be the problem, that's great, but the fix hasn't made it to any store bought amp I've ever heard... and I've heard a lot of them. Also, there's no point in comparing guitar amps to hi-fi amps. A 20' Chris Craft with inboard motors and a Honda Civic both run on gas... but they can't do the same job. I'm not interested in making waves or upsetting anyone's applecart. This is just a personal opinion developed over 48 years of playing guitars through amps. I hope it helps those that have had the same experience as me, or at least gives someone something to think about.
Thanks,
Dave

[sluckey]

I was not trying to compare hifi amps and guitar amps. They are definitely two different animals with two totally different goals. Hifi is all about true reproduction while guitar amps are all about adding lots of color to the lifeless sound produced by an electric guitar pickup. I know the amp is a huge part of the sounds I like.

I used the old Fisher simply as an example that EL84s or 6BQ5s can be run at high plate voltages and still sound fine. There's much more to consider than just the plate voltage. That's the point I was trying to make.

[Tiny_Daddy]

I have used a cheap isolation transformer with voltage doubler to get a voltage for the EL84. Separate filament transformer required, also cheap.

[bluesbear]

Whoops! I didn't mean at point to anyone about anything. Anyway, it seems to me we're actually in agreement. I know there is more than one way to skin a cat (apologies to my cat!). There's too many designs of too many amps using too many tubes to do them all. I don't have the time or money to do the total research thing so once I get the sound I'm after, I go on to something completely different. I'm glad someone is doing what I can't (or won't bother with). My favorite part about amp building is that there are so many ways to get to a certain point. That's why I consider it more of an art than a science.
My respects to everyone's opinions and designs! The only wrong idea is the one that doesn't get tried.
Dave

[jojokeo]

Bluesbear, check this out. It came from Blackie Pagano's site describing a custom amp called Grand Champion he designed & built. It describes what you're feelings are I believe in that "low and hot" to me implies low voltage but biased hot to max power dissipation (even if they aren't EL84s in this example, the theory remains the same)?

From Blackie, "It sounds like it looks - familiar yet unique.

You will notice that this amp makes some serious heat. The dual 6550 / KT88's are in a deep Class A operating point, with a relatively low voltage swing and very high current, running at their design maximum of 40w heat dissipation per tube. The transformers and tubes are running at full tilt, like a top fueler with the hammer down, even with no guitar signal applied.

The "low and hot" operating points for audio tubes are suggested by the original engineers of these tubes in the ancient tube manuals as giving a optimally pleasing and musical sonic spectrum with even-order harmonics predominating. These classic operating points are rarely exploited in the guitar amp design world as they yield lower power numbers than the typical higher voltage swing class AB operating points. Although "low and hot" operating points are rare in guitar amps they are revered in the world of underground audio as the operating points of choice for dimensional, dynamic tube sound that transitions to distortion gracefully.

This power section and driver stage work together to create a fairly high powered amplifier (approx. 25 watts) in which even-order harmonics predominate at all gain levels. You will no doubt notice that the sonic characteristics of the "Grand Champion" somewhat resemble a Fender tweed Champ, but with 10x more power and voiced brighter to more modern standards. In fact, the waveform this amp makes is almost identical to a Tweed Champ (soft, asymmetrical 2nd harmonic clipping characteristics) but with a lot more juice. Another difference is that the "Grand Champion" has a good deal more drive and can be pushed into a crazy distortion, going from a moderately loud clean tone with a sweet holographic midrange though a singing bluesy and aggressive lead tone all the way to a fragmented and psychotic fuzz, which can be tamed with the single high-end rolloff control and the master volume, both of which I recommend leaving wide open for normal use."

[phsyconoodler]

All we were trying to point out is that it's NOT the plate voltage that makes an EL84 amp sound brittle of too spikey trebly.It is the circuit design that you don't like on the EL84 amps that you've tried.
 I had a Traynor Guitar Mate amp that was so brown and creamy sounding I was quite surprised to find it had 420v on the plates.

[samato]

All we were trying to point out is that it's NOT the plate voltage that makes an EL84 amp sound brittle of too spikey trebly.It is the circuit design that you don't like on the EL84 amps that you've tried.
 I had a Traynor Guitar Mate amp that was so brown and creamy sounding I was quite surprised to find it had 420v on the plates.

That's what I read and understood from Dave Hunter's book, which was one of my first learning tools for this stuff.  It's not any one variable in an amp that makes the sound, it's all of them.  The overall design.  One thing compensates for another, etc., etc.

[jojokeo]

All we were trying to point out is that it's NOT the plate voltage that makes an EL84 amp sound brittle of too spikey trebly.It is the circuit design that you don't like on the EL84 amps that you've tried.
 I had a Traynor Guitar Mate amp that was so brown and creamy sounding I was quite surprised to find it had 420v on the plates.

I was just pointing out something somebody else designed and described that I think corresponded w/ what B-bear was also saying. I never made this thread's connection myself. I do wonder why there seems to be so many higher voltage PT's available and so few that are made in the lower voltage ranges w/ various _mA/6.3 _Amps options and why conventional thinking seems to be, "tube spec says max voltage is listed as 300v, hmmm...we must run it up to 420+ volts! Yeah, that's the ticket!"

This issue only seems to be associated to EL84s, & 6V6s also. It's not nearly as common to find EL34s and 6550's ran way over their voltage specs. (I can think of a number of reasons but those aren't the point here) So going by that analogy if running tubes over their ratings was so advantageuos then EVERY power tube would be pushed way over their voltage ratings. It leaves one to wonder about these inconsistencies in design and our explanations in trying to interpret or put a spin on the subject to justify our points of view? There's no right or wrong here. Simply because there's an amp out there that subjectively sounds one way or the other isn't enough to justify a conclusioin.

Sorry, I'm not trying to act the know it all fool, rather quite the opposite. I understand the many many variables that all contribute to the outcome of our amps and it does make this subject way more complicated to reason through. Changing a speaker or tube alone can make all the difference when we may attribute our issue related to voltage? That doesn't cross my mind as much when I'm dialing in my amps. Ultimately it seems to be more like, "should I bake my double chocolate brownies at 300, 325, or 350 degrees?" All the temps will work but is there a difference in taste? Now where's that Betty Crocker recipe? I bet Emeril, Wolfgang Puck, or even the Soup Nazi  don't think like that?  It seems to be more like the Ronco EZ Bake oven - just set it and forget it. 

[phsyconoodler]

It's the CURRENT that runs through that tube that makes it work too hard.The screens as well.
  You can run it at pretty much any reasonable voltage and taylor the rest of the amp to work any way you want it.
What I hear bluesbear saying is that he tried a few stock layout EL84 amps that had higher plate voltages and they were harsh sounding to him.This is not simply a taste thing here,it's true.
  But it does not address the issue.The issue is that the 'stock' layouts often did not use the higher voltages that some EL84 amps end up with today.The original Marshall 18 watt is one example.The original Watkins Dominator and Marshall 1974 had around 300v on the plates and the newer builds ended up with more like 350v and more.Without compensating for that extra voltage they sound harsg-her than their vintage cousins.
  But......if you do what I ended up doing with a few 18 watt builds,they sound awesome with the stock layout.
 I use a Hammond 270FX PT with an NOS 5Y3 rectifier to get about 302v on the plates.When you use the 290-0-290 PT that Heyboer uses the B+ ends up around 350v with the EZ81 rectifier tube.

[Platefire]

Maybe thats' why my SE EL84 Little Bear amp sound so sweet at 288V on plate. I've been wanting to build one of those 18 watt Marshalls a long time. Thanks for the tip on the lower voltage transformer.

I do have a Mesa Boogie Rocket 440 with 4-EL84's that sounds really good--never have cracked out the chassis to check any voltages yet, just played the fire out it. Platefire

[jojokeo]

It's the CURRENT that runs through that tube that makes it work too hard.The screens as well.
  You can run it at pretty much any reasonable voltage and taylor the rest of the amp to work any way you want it.

Agree totally. The VVR circuit really helps w/ this understanding. The voltage changing by small amounts doesn't really change the tone perceptively until it's made a fair amount. I used to just blindly throw in a 130r cathode resistor for el84s or 250r for 6v6s for example but now I always work out the Pd formula to know exactly where I'm at. With some unconventional designs & tubes I've made & used over the last year or more, I've had to learn to do that.

[Tone Junkie]

jojokeo what is the PD formula so us rookie can figure it out to. Thanks Bill

PS I havnt learned anything usefull about amps all day. And sounds like that would be good for a weeks worth 

[Geezer]

Here's how I do it on cathode biased tubes.....

*MEASURE the ACTUAL value of the cathode (bias) resistor (while it's COLD)......write it down

*Turn on the amp, let it warm a bit (but if this is a new build, keep an eye on the plates of the power tubes....you could be WAY off on bias & they could redplate from too much current)

*MEASURE the plate voltage by placing your red probe on the plate & your black probe on the cathode. (this will automatically give you actual plate volts, which is plate voltage minus cathode voltage.....you can also measure the plate volts & cathode volts separately & subtract)....write down the voltage

*Measure the cathode voltage (red probe to cathode, black to ground)....write it down


Now, let's say you recorded the following:

Rk = 120 ohms
plate to cathode voltage = 300vdc
cathode voltage = 13.3vdc

take the cathode voltage (13.3) & divide it by the cathode resistor value (120)
13.3/120=0.111

divide the result (0.111) by the # of tubes (let's say it's an 18watter, so 2x tubes)
0.111/2=0.055

mutiply the result (0.055) by the plate voltage (300v)
0.055*300=16.5w

The plate a dissipating ~~16.5 watts, too much for the 12-14w rated EL84's, so sub another cathode resistor (higher value, maybe a 150 ohm?) & do all the measurements & calculations again, because EVERYTHING will have changed.

G

[jojokeo]

Thanks Geezer, you're always a big help!

[Tone Junkie]

Thanks Geezer another fine piece to go on my wall of important info. Bill

[Ritchie200]

I just ran across this amp on u-toob.  It's the new Carvin V3M with 4-EL84's.  Tiny little amp.  Switchable between 7, 22, or 50 watts.  You know they are cook'n those four 84's to get 50 watts.  Four AX7's.  I listened to a demo clip from the NAMM show.  Holy crap this thing sounds good.  Maybe some of the definition comes from the headroom?  I'd sure like to see the schemo on this thing....  Carvin has always had EL84 amps in their product line.  I'm sure they got them lined out by now!

Jim