EL84 max power for HiFi Amp

[hoyhoysum]

Hi, i am a newbie here and i guess this must be another boring question again. I would like build to start first my first tube amp, i have done many transistor and ic amps before. I would like to start from scratch! Later i will built a phono stage to intergrate with it. I don't know why but i would like my amp with built in phono stage.

I would like to build using a pair of EL84, pentode mode, fix bias, 43% ultraliner connection. I need the maximum wattage i can squeeze from a pair of them with decent hifi quality sound(Asuming i use generally available el84 tubes, no special tubes involved) Here are my questions,

1) What is the max wattage i am looking at at?

2) What is the best max voltage that i can applied to the CT of output transformer, can i safely say it to be the plate voltage? I need the tube to last for quite some time also.

3) What are the specifications of output transformer that
i need to buy?

4) Any circuit ideas or schematic i can start of with.

Thanks in advance.

 

[kevinkr]

Hi, i am a newbie here and i guess this must be another boring question again. I would like build to start first my first tube amp, i have done many transistor and ic amps before. I would like to start from scratch! Later i will built a phono stage to intergrate with it. I don't know why but i would like my amp with built in phono stage.

I would like to build using a pair of EL84, pentode mode, fix bias, 43% ultraliner connection. I need the maximum wattage i can squeeze from a pair of them with decent hifi quality sound(Asuming i use generally available el84 tubes, no special tubes involved) Here are my questions,

1) What is the max wattage i am looking at at?

2) What is the best max voltage that i can applied to the CT of output transformer, can i safely say it to be the plate voltage? I need the tube to last for quite some time also.

3) What are the specifications of output transformer that
i need to buy?

4) Any circuit ideas or schematic i can start of with.

Thanks in advance.

So UL mode (rather than pentode mode) - about 15Wrms for a single pair. (Some vintage designs made as much as 20Wrms, but modern 6BQ5 are not up to this.)

I would not go much over 300V with any currently made 6BQ5, 6P14P-EV maybe 350V maximum.

An output transformer for the Dynaco ST-35 (Z-565)(www.dynakitparts.com) would be a good choice, but anything around 8K PP with UL taps would be fine. (Edcor makes some nice transformers as well.)

The requirement for long life and high power with modern tubes is unfortunately something of an oxi-moron. What do you mean by long life? A couple of years or more?

Also recommend you get Morgan Jone's Valve Amplifier's 3rd Edition and Building Valve Amplifiers.

Search around here for designs you can build. I believe there are several. Probably SY or ELI can make more specific recommendations. (I'm into SE, sorry.)

As a newbie you should carefully read the safety and high voltage thread here.

 

[boywonder]

Search for Gingertube's Baby Huey or Sy's Red Light District.

Plan on 10-15 Watts depending on your B+ voltage.

Hammond 1608 (8K/10W) or 1650E (8K/15W) transformers are popular cost-effective O/P transformers, as well as the dynaclone mentioned above.

 

[planet10]

Search for Gingertube's Baby Huey or Sy's Red Light District.

and Eli's El Cheapo -- can easily be reconfigured for UL.

dave

 

[aardvarkash10]

Or to raise the simplicityutput ratio...

http://diyparadise.com/web/index.php?option=com_content&task=view&id=58&Itemid=26

 

[hoyhoysum]

What is the difference between UL connection and Pentode mode in terms of sound quality and max wattage that it can produce?

I have the Morgan Jones book, it is a good book! The book shows a design for 10Wrms with self biased( cathode bias). I used to own an audio innovations 200 power amp, it sound goood but sound comppressed(valve clip) when push hard. I regret selling that amp away. i am sure the output design is similar to the morgan jones design. I want something more watts to drive most commercially available speaker with low sensitivity.

I recently found out that Jolida JD102 produce 20Watts and max 25 W with a pair of el84. How did it mnage to do it? I am curious. Please do not ask me to flip it upside down to check it out coz this amp does not exsist in our part of planet.

Your valuable input is most appreciated!

 

[aardvarkash10]

don't tip the amp unpside down...

...tip the manufacturer upside down. WHile you are at it, think about the MANY different definitions of the phrase "maximum power" For example PMPO (often quoted on Korean manufactured cheep'násteee stuff) as against RMS...

 

[Yvesm]

What is the difference between UL connection and Pentode mode in terms of sound quality and max wattage that it can produce?

Wattage and quality seldomly come together !
Yes, you can probably extract 20 watts from a pair of EL84 driving them very hard, but don't expect clear sound nor long life

I have the Morgan Jones book, it is a good book! The book shows a design for 10Wrms with self biased( cathode bias). I used to own an audio innovations 200 power amp, it sound goood but sound comppressed(valve clip) when push hard. I regret selling that amp away. i am sure the output design is similar to the morgan jones design. I want something more watts to drive most commercially available speaker with low sensitivity.

Perhaps, power could be increased a bit using fixed bias for exemple, but 10 or 20 % more watts (+0.8dB) is barely noticeable while 10% more distortion definitly is.

Having the same sound level from an 80dB speaker than from an 90dB one calls for multiplying the applied power by 10 ! !

The only path is to use bigger tubes, bigger OPTs and bigger supply !
Sorry, no free beer !

Yves.

 

[azazello]

I think, for realy Ni-Fi and Hi-End You must have - Speaker 92-95 db /in box
or in horne/ and ampl. SE, only A class. 6S4S, 6S41S, EL 34......are
bether PP EL84. The sound of PP is something metallic, when there is
switch over upper to bottom EL84, I think.

 

[cerrem]

A few things to keep in mind....
The power output will be lower in PP Class-A then PP Class AB1 for a bit more watts.... The trick to not blowing up EL84 valves when using higher plate voltages is to keep the screen voltage no higher than 300V.... I have safely operated EL84 valves with 390V on the plates and 280V on the screens....
UL mode is nice when operated linearly...meaning you don't push the amp to hard... UL will "pass" square wave nicely when well designed..However, when you push the UL stage into clipping it is not pleasant.... This is due to significant drop in screen grid impedance, thus screen current draw durring transient operation... One classic design that is very simple is the Fisher SA-100 circuit that used a 12DW7 with a pair of EL84's per channel...
This was a descent EL84 amp to adapt... and it is not UL ....

Chris

 

[Eli Duttman]

To squeeze the absolute max. power out, pure pentode mode is required. Pure pentode comes with its share of baggage. Regulated g2 B+ is very much in order. CONSIDERABLE NFB of 1 sort or another is necessary, to obtain a satisfactory damping factor.

Paper claims and theoretical arguments to the contrary, "12" WPC is what you get from UL mode and "15" WPC is what you get from pentode mode, in the real world.

FWIW, a pure Class "B" PP pair of EL84s, operated within published limits, yield a theoretical max. O/P of 19.6 W.

 

[alexg]

I recently found out that Jolida JD102 produce 20Watts and max 25 W with a pair of el84. How did it mnage to do it? I am curious. Please do not ask me to flip it upside down to check it out coz this amp does not exsist in our part of planet.

Did you measure the output or it is on their marketing brochure?

 

[Diomedian]

Music Reference RM-10

I don't know why more noise hasn't been made about this amp on DIY Audio, but Roger Modjeski's RM-10 from Music Reference throws 35W from a single pair of EL-84s, and he still claims 10,000 hours life on the tubes, and just a 70W draw at idle.

http://www.ramlabs-musicreference.com/rm10mk2.html

Apparently the schematic is reprinted in the user manual, but I haven't seen it.

-d

 

[Eli Duttman]

Re: Music Reference RM-10

I don't know why more noise hasn't been made about this amp on DIY Audio, but Roger Modjeski's RM-10 from Music Reference throws 35W from a single pair of EL-84s, and he still claims 10,000 hours life on the tubes, and just a 70W draw at idle.

http://www.ramlabs-musicreference.com/rm10mk2.html

Apparently the schematic is reprinted in the user manual, but I haven't seen it.

-d

To be charitable, the incumbent administration has been lax in enforcing thruth in advertising laws. All sorts of claims have, and will continue to be, made. When did G_D repeal the Laws of Physics? VERY well established theory informs us that Π/4 is the max. efficiency that can be obtained from pure Class "B" amplifying devices. A PP pair of EL84s can safely dissipate 25 W., on average. Do the arithmetic. It is painfully obvious that the claims are utter rubbish.

 

[planet10]

Re: Music Reference RM-10

Music Reference RM-10

Be interesting to put it on the bench... claims sound kinda far-fetched. And the binding posts are pretty ugly.

dave

 

[Diomedian]

Well I don't claim to understand what's going on, but Modjeski's no dummy marketer - maybe this review from Six Moons will shed some light - he gives some insight...

http://sixmoons.com/audioreviews/musicreference/rm10.html

If nothing else, it shows the insides of the amp.

Modjeski himself replies to some of the disbelievers on this thread on Audio Asylum. Maybe you can make something out of it:

http://www.audioasylum.com/audio/tubes/messages/6/60896.html

-d

 

[DougL]

From the 6Moons review.

Increasing the idle plate voltage, decreasing the idle plate current and increasing the load resistance to optimum can greatly increase operational efficiency,

Looks straightforward. Class AB pentode.
If you assume class A triode, its not possible.

Bias is set to 35 Ma per channel, including the driver.
That works out to 15 Ma per tube.

Probably a nice amp. Not something I will DIY.

Doug

 

[Ty_Bower]

Bias is set to 35 Ma per channel, including the driver.
That works out to 15 Ma per tube.

From what I can pick out, the plate voltage is 700 V. Screens are held at 350 V.

 

[hoyhoysum]

Thanks for the lead, this is something i would like to take a look and diy.

In my country when i inquire about output transformer for el84, the shopkeeper will tell me save my effort and time just buy a ready made China amp for USD150. Not worth to place an order for those output trans. Those they stock are for those el34...
They are abudant of 10-12 watts amplifier in the market and abudance of circuit in the internet.

This design i will definite like to take a look. If i can achieve more than 20Wrms i will be very happy...

I am still in the dark as to how he can achieve it, if some care to explain to me....

 

[Ty_Bower]

I put together a quick and dirty model using LTSpice. I started with a schematic modeled closely after the Dynaco ST35. I wired a fixed 700V supply to the plates and a fixed 350V supply to the screens. I assumed roughly 1000 ohms cathode resistance to set the idle current at approximately 15 mA per output tube. I am aware that Roger actually uses a fixed bias topology in his RM-10.

According to the model, you can indeed get a clean looking 48 volt swing (peak to peak) into an 8 ohm load. That will net you the 35 watts per channel that Roger claims.

Whether or not it is reasonable to believe the spice model of the 6BQ5 is valid at these voltages is a questions that should be considered. It is also worth considering the 1.3 kV peaks that will be seen at the plates when operating under these conditions.