How many watts from a pair of EL84's?

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How many watts from a pair of EL84's?

Postby joeriz » Thu Mar 05, 2009 9:30 am

I'm wondering...

How many watts is it possible to squeeze from a pair of EL84s? I know that most stereo amps that use a pair per side get rougly 14-17 watts per channel. But then there are amps like the Music Reference RM-10 that claim to be able to squeeze 35 wpc from a pair. Yellow_Light_Colorz_PDT_23

How about 7189's? I'm assuming based on the tube specs that one can get a few more watts out of them.

I wouldn't mind building an EL84/7189 based amp that could do, say, 25-30 watts per channel. I'm sure I'd need a power tranny bigger than the PA774. How about the output transformers? Would a pair of Z565's be up to the task or would I need something bigger?

Tube life shouldn't be a huge issue given the relatively low price of EL84s/7189s.

Thanks,
Joe
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Postby TomMcNally » Thu Mar 05, 2009 10:16 am

I would say the RM-10 is using some trickery, or the tubes
only last a few weeks.

If you want more power, I'd say go with bigger tubes.

... tom
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Postby joeriz » Thu Mar 05, 2009 10:34 am

Thanks, Tom. Or I suppose I could parallel a pair of EL84s. I'm really looking to stick with that EL84 sound.

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How much power from a pair of EL-84s

Postby Lafish » Thu Mar 05, 2009 3:45 pm

Tom wrote:
I would say the RM-10 is using some trickery, or the tubes
only last a few weeks.

I don't think there's any trickery, except that Roger Modjeski wrote his own application instead of using the old manuals, and tube life is just fine.

More here: http://www.ramlabs-musicreference.com/rm10design.html

and here:
http://www.6moons.com/audioreviews/musi ... /rm10.html
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Postby Ty_Bower » Thu Mar 05, 2009 3:57 pm

If there were no laws of physics broken, surely someone else must have built a 35wpc EL84 amp. Where is it?
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Postby Geek » Thu Mar 05, 2009 4:30 pm

They certainly cannot produce 35W and the best I have got out of them is 25W with 450V and about 50% over specs everywhere.

It must be a hybrid with a MOSFET "helper" in parallel with the tubes or something.

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Red is dead...

Postby EWBrown » Thu Mar 05, 2009 7:11 pm

They could produce 20-25W in fixed bias pentode mode, and around 400V BV+, but that's really pushing them hard. This is best done with 7189As or the СДЕЛАНО В СССР (Russian) 6P14P-EVs.

Other "lesser" EL84s may or not survive for long in this kind of service. J/Js may develop red plate-itis under such conditions :o Yellow_Light_Colorz_PDT_11

I've seen some PPP EL84 amps which can produce 45WPC in pentode mode, and about 25WPC in triode mode, from VTL and Manley Labs. They run around 400VDC B+ and fixed- bias the tubes @ 30 mA rather than the "standard" 35 mA. That still keeps 'em around 12W PD. The VA and LTPI use 12AT7s, and is very similar to Roy Mottram's "VTA-70" driver board, with some minor resistor value adjustments.

The RM-10's 35 Watts seems extreme, I wonder about the methodology of their "specsmanship"... Yellow_Light_Colorz_PDT_11

OTOH, getting 22-25 WPC out of a pair of 6CW5/EL86s is indeed possible, with a B+ around 260V, idling current of about 60mA per tube, amd up to 120-130 mA each during peaks. These would be running in hard AB2 territory. OPT should be around 3.3K A-A, use a 6600 ohm PP OPT and load the 16 ohm secondary with 8 ohms, aand that would reflect back to the tubbes as 3300 ohms, and no "special" custom trannies would be needed. 15CW5/PL84 (not PL84) would be the cheap tube version.

I'd SWAG approx 430-470 ohms, 5W or greater RK for each 6CW5, bypass with 470-1000 uF / 50V (or greater) caps. Fixed bias may be a bit "risky" under these operating conditions :o

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Re: Red is dead...

Postby Geek » Thu Mar 05, 2009 8:13 pm

EWBrown wrote:They could produce 20-25W in fixed bias pentode mode, and around 400V BV+, but that's really pushing them hard. This is best done with 7189As or the СДЕЛАНО В СССР (Russian) 6P14P-EVs.


That's what I used in my test. The 6P14P's actually survived, while the 7189's didn't Yellow_Light_Colorz_PDT_24


Other "lesser" EL84s may or not survive for long in this kind of service. J/Js may develop red plate-itis under such conditions :o Yellow_Light_Colorz_PDT_11


Or Ei's. MAN, I have never had such crap amp output tubes (at least for geetah) Yellow_Light_Colorz_PDT_21

(edit)
Ok... maybe TAD's


I've seen some PPP EL84 amps which can produce 45WPC in pentode mode, and about 25WPC in triode mode,....


These in PPP - the AX84 crowd has done some insanity there Yellow_Light_Colorz_PDT_07

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Re: How many watts from a pair of EL84's?

Postby Roger A Modjeski » Sat Mar 21, 2009 11:49 am

joeriz wrote:I'm wondering...

How many watts is it possible to squeeze from a pair of EL84s? I know that most stereo amps that use a pair per side get rougly 14-17 watts per channel. But then there are amps like the Music Reference RM-10 that claim to be able to squeeze 35 wpc from a pair. Yellow_Light_Colorz_PDT_23

How about 7189's? I'm assuming based on the tube specs that one can get a few more watts out of them.

I wouldn't mind building an EL84/7189 based amp that could do, say, 25-30 watts per channel. I'm sure I'd need a power tranny bigger than the PA774. How about the output transformers? Would a pair of Z565's be up to the task or would I need something bigger?

Tube life shouldn't be a huge issue given the relatively low price of EL84s/7189s.

Thanks,
Joe


Joe and all,

Thanks for your thoughts. The RM-10 actually produces 40 watts one channel driven, 35 x 2 both driven and 70 watts in the mono mode selected by a switch on the rear. All this is done without exceeding the 12 watt dissipation rating of the tube and actually runs the tubes cooler than a Dynaco Stereo 35. I know because I have measured it and the tubes last longer.

The mono mode in this amp is also unique in that it does not parallel the channels in the typical way. Thus it does not require resistors in series with the output to keep them from fighting each other as Dynaco requires in the ST-70 and other amps. Those resistors reduce power and damping and still only reduce, not remove the problem.

The tube life is in excess of 5000 hours. There are no tricks, no transistors, no squeezing. The application is not in the books. I created it through my own research and tested it for 5 years in my home driving Quad ESL 57, ESL 63 and Vandersteen 2CI speakers. I designed the special transformers it requires and wound them myself.

More on this and other tube applications can be found at the Music Reference circle on Audiocircle.com. I recommend our circle for those interested in thinking out of the box (or data book in this case).

http://www.audiocircle.com/circles/inde ... ic=66232.0
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Postby evsentry3 » Mon Mar 23, 2009 7:03 pm

Thanks for signing up here Roger and dropping in your comments!

I'd have to say, the RM-10 is not just an out of the box design, it also is exceedingly nice sounding too! Paired with a Zu Druid, the music can just stop you in your tracks with it's magic! It did me!!

At Hi-Fi shows over the years I've been lucky enough to go to, at a lot of small audiophools get togethers and around lots of DIY stuff, every once in a while you run across something that just makes that music so well! That accomplishes that fun we spend so much time in pursuit of. The RM-10, one of my top surprises!!

The RM-10, in several chances to hear it now, is really something very nice and well worth going out of your way to hear! It nabs you with that typical EL-84 swagger and somehow still has the finess to give you the inner detail and the part of the music that sucks you into good music and even can even change your mood if the music calls for it! Has really made me want to hear some of the others in the line...

It raises the bar on what we expect from our systems and it's certainly fun to say that it shouldn't be able to do what it does! Bravo!!

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Postby Ty_Bower » Mon Mar 23, 2009 7:36 pm

This topic was discussed last fall. The thread can be found here: http://www.diyaudio.com/forums/showthre ... did=131829

I offered some of my guesses regarding what is going on in the RM-10. Others pointed out why my theories don't hold up. I do not believe any significant conclusions were drawn. No one has offered any schematics or exact details of the operating points. I suppose someone will need to buy one of the darn things and dissect it to find the answers. I was curious enough to write to Roger and ask a few questions. His response was prompt, polite, and intelligent. He suggested I might be able to purchase a transformer set and schematic from him, but I was not inclined to pay the asking price.

Another one of the many unexplained mysteries of the universe... :?

FYI, Roger posted an explanation of how the amplifier achieves its rated output. Read his post here: http://www.audioasylum.com/audio/tubes/ ... 61139.html
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Postby Roger A Modjeski » Mon Mar 23, 2009 11:29 pm

Ty_Bower wrote:This topic was discussed last fall. The thread can be found here: http://www.diyaudio.com/forums/showthre ... did=131829

I offered some of my guesses regarding what is going on in the RM-10. Others pointed out why my theories don't hold up. I do not believe any significant conclusions were drawn. No one has offered any schematics or exact details of the operating points. I suppose someone will need to buy one of the darn things and dissect it to find the answers. I was curious enough to write to Roger and ask a few questions. His response was prompt, polite, and intelligent. He suggested I might be able to purchase a transformer set and schematic from him, but I was not inclined to pay the asking price.

Another one of the many unexplained mysteries of the universe... :?

FYI, Roger posted an explanation of how the amplifier achieves its rated output. Read his post here: http://www.audioasylum.com/audio/tubes/ ... 61139.html



Thanks for the link. That was so long ago I had forgotten. I'd say the cat has been out of the bag since then. Here's the information that is important to the application taken from the link at the bottom of the link Ty kindly posted.

Let me go through the numbers and tell you how I get more than the specified 35 watts. Actually at the plates of the tubes, where all the tube manuals (bibles) take the data, I am getting about 45 watts. Some of you have misquoted the bias, dissipation and done some poor math, so sharpen your pencils. First the bias is indeed 30 ma. but for the pair of tubes and measured across 10 ohms, hense the 300 mV set point. Though 25 ma will double the tube life, (under light loading or soft playing) it will increase the distortion. Since the tubes are cheap, I let people decide for themselves. At the 700V B+ (yes, 700) the idle dissipation is 21 watts/pair or 10.5 per tube, well within the 12 watt rating. The screens run at 350 V and very cool, further enhansing the tube life. (The opposite of many designs like David Manley and early CJ). It's not the plates that mind the HV, it's the screens.
The only thing missing from the above to make it a complete application is the following. Load: 13,000 ohms PP, max signal current: 100 mA. Fixed bias: -25V (varies widely with tube maker, something that affects the sound of all those cathode biased EL-84 amps).

This is not a cathode biased amp so stop comparing it to cathode biased amps which make up 99% of the EL-84 amps out there. The main application of the EL-84 was single ended and push-pull amps in phono/radio consoles. The cathode bias and low plate voltages made the circuit simple and the TV Repairman didn't have to adjust anything, just replace the burned-up tubes. So why are we guilding the lilly of circuits used by Magnavox, Zenith, Motorola and Dynaco when the tube is capable of much more.

If there is enough interest I will look into the pricing of a transformer set or a kit. If I got orders for 100 kits I would do it. Otherwise it takes less time to build one than to kit-up the parts for any fewer. For those who like exotic parts; the hand-wired chassis has plenty of room and substitution is very easy. Gain/damping setting is also easily done.

I love to make things for myself and a great deal of my test equipment is self-made because I sometimes need is not made. I recall something a professor at U of VA told me when I said I like to make my own stuff "If someone manufactures what you need it's less expensive to buy it than make it yourself". To make that statement a bit more appealing I will offer, for a limited time, brand new, fully warranted RM-10 MKII's to this forum at a $500+ discount making the price $1,450 shipping included (that's the +). http://www.ramlabs-musicreference.com/rm10mk2.html. Also see the design philosophy section listed on the home page.
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Postby Geek » Tue Mar 24, 2009 3:23 am

*edit*

NM, I just saw the B+. Will try.

Cheers!
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Postby Roger A Modjeski » Tue Mar 24, 2009 10:16 am

Note the 350V screen, 15mA/tube bias and 13,000 ohm load.
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Postby TerrySmith » Tue Mar 24, 2009 2:00 pm

I know for a fact Mr Modjeski builds a quality product. I used to own a RM-9 #471 for about 12 years.

He claimed 10,000 hours from the EL34's, in actuality they came close or maybe passed that. Bias was checked from time to time, and barely moved over the course of time. After 9 or 10 YEARS, one of the EL34's went pyro, had to replace the tube fuse and the LED in the bias circuit, and the EL34's. I still have the other 7 EL34's, they still test very strong.
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