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Old 23rd October 2008, 04:10 PM   #1
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Default EL84 max power for HiFi Amp

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.
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Old 23rd October 2008, 04:24 PM   #2
kevinkr is offline kevinkr  United States
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Default Re: EL84 max power for HiFi Amp

Quote:
Originally posted by 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.

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.
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Old 23rd October 2008, 05:10 PM   #3
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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.
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Old 23rd October 2008, 06:35 PM   #4
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Quote:
Originally posted by boywonder
Search for Gingertube's Baby Huey or Sy's Red Light District.
and Eli's El Cheapo -- can easily be reconfigured for UL.

dave
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Old 23rd October 2008, 07:21 PM   #5
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Default Or to raise the simplicity:output ratio...

http://diyparadise.com/web/index.php...d=58&Itemid=26
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Old 24th October 2008, 04:00 AM   #6
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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!
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Old 24th October 2008, 06:44 AM   #7
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Default 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...
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Old 24th October 2008, 07:21 AM   #8
Yvesm is offline Yvesm  France
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Quote:
Originally posted by hoyhoysum
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
Quote:

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.
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Old 24th October 2008, 09:42 AM   #9
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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.
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Old 24th October 2008, 02:11 PM   #10
cerrem is offline cerrem  United States
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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
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