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Old 1st July 2005, 07:41 AM   #21
cerrem is offline cerrem  United States
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Here is the EF86 schematic...
Use just the first stage......
I remember that I recalculated the R and C values to getter a tighter RIAA curve....can't find the notes right now...

My free picture Host will not support the size of this PDF....
SO I will Email it to you...

Chris
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Old 19th August 2008, 10:19 PM   #22
lineup is offline lineup  Sweden
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Quote:
Originally posted by cerrem

Here is the EF86 schematic...
Use just the first stage......
I remember that I recalculated the R and C values to getter a tighter RIAA curve....can't find the notes right now...

My free picture Host will not support the size of this PDF....
SO I will Email it to you...

Chris
Chris,
can you email EF86 schema to me, too.
I have always been a great EF86 fan.
Simple is one good tube .. for small signal audio circuits.

thanks, lineup
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Old 21st December 2009, 01:35 AM   #23
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Quote:
Originally Posted by gmilitano View Post
I will likely give the RCA schemtic a whirl with 12AX7.

Here is another simple design I came across:

http://www.turneraudio.com.au/htmlwe...implephono.htm
I would like to mention that this schematic will be a noisy one. Because of the 12ax7 being so high in gain i recommend a different approach. There are 4 things to account for in an RIAA preamp:

1 - LOW noise.
2 - Good RIAA curve, passive equalization is better but B+ must be somewhat regulated to be more accurate if this is to be used instead of negative feedback.
3 - A reasonable output impedance.
4 - Enough gain depending on what cartridge you are using.

I have tried to build a simple 12ax7 phono preamp in the past similar to this schematic and i really recommend using parallel triodes for the first stage followed by an SRPP configuration at the end to achieve a bit more gain and to get an output impedance roughly around 10k instead of 60k in a conventional 2 stage 12ax7 design. Using parallel triodes for the first stage greatly lowers the noise floor.

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Old 10th January 2010, 05:25 AM   #24
Ivey is offline Ivey  United States
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Here it is, we have entered into the year 2010. And no one has answered or referred to your original question or request. A Phono PreAmp using a 12AU7.

They all speak about the 12AX7 or some other tube. And not the one that you are interested in using. The 12AU7.

I regret that I was not a part of the DIY Audio earlier to assist. I was a Aerospace Electronic Engineer for Lockheed Martin. As well, I worked for other companies designing and building military tube electronic equipment in the 1950's and 60's.
so I have a great deal of experience with tubes and their use in circuits.

So lets get started on that PreAmp, if anyone wants to know.

The 12AU7 is an excellent tube for Phono PreAmp use. In fact, it is better than the 12AX7 and any of the others that most audio expects babble about.

In my day we used the 6SN7/12AU7, but they are the same. The problem is gain. You must over come the gain issue to use it with the MM cartridge. And to do that with a 12AU7 or a 6SN7, you can not use passive RIAA. It must be active. You will lose gain in a passive circuit. You must use active.

the Phono PreAmp is made up of 2.6 to 2.85 gain stages. That is two common cathode and one cathode follower stage. The RIAA is one of the clever circuits we came up with. It covers the entire LP range. It is only three components. Two caps and a resistor.

So you will need three 12AU7's for a stereo phono preamp.

Power Supply is very simple as well. Two 12volt 2amp transformers connected reverse. and two transistors, two or three high voltage zeners and some resistors and caps. for the regulator.

I will post the drawing soon. It is a dandy.

Take Care


Ivey.
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Old 10th January 2010, 01:45 PM   #25
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Ivey,

Welcome to the forum.

Quote:
...Lockheed Martin. As well, I worked for other companies designing and building military tube electronic equipment in the 1950's and 60's.
so I have a great deal of experience with tubes and their use in circuits.
Would you have any suggestions for the use of the 5703 miniature? Several have been resting in my parts bin w/ a phono stage in mind.
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Old 10th January 2010, 02:32 PM   #26
ebw is offline ebw
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Ivey:
I just joined diyAudio e few minutes ago, and found your thread. It reminds me 40 years ago when I used to work with tubes in constructing my transmitter for amateur radio (when I was in high school). Well, I am interested in Phono pre-Amp, Please send me also the diagram and inform all things needed (i.e. three 12AU7's, power Supply two 12volt 2amp transformers connected reverse (how to do it?). and two transistors (what transistors and how is the connection), two or three high voltage zeners (what is this?), and some resistors and caps (pls specify the specifications). Thanks.
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Old 10th January 2010, 03:53 PM   #27
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With all respect, the 12AU7 and 6SN7 are different "animals". Yes, μ (20) and operating conditions are "the same". However, linearity is not. The 6SN7 is beautifully linear, while the 12AU7 is downright ugly. I've said it before and I'll say it again, restrict the 12AU7 to cathode follower and "concertina" phase splitter duty, in HIFI service.

It might be possible to use passive EQ and 6SN7 family tubes in a RIAA preamp. At 2.6 mA./V., gm is reasonably high. A good deal of gain could be obtained from cascoded sections DC coupled to cathode followers. A pair of such gain blocks, with the EQ network between them, seems feasible. The $64 question of "What's the S/N ratio?" hovers in the air.
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Old 11th January 2010, 05:11 PM   #28
Ivey is offline Ivey  United States
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Default Ebw

I am also a Ham Radio operator too. I do not do much hamming since I moved from Hawaii to California.

In Hawaii, I worked with the government on cold war electronic projects.

I was first licensed in 1958. But I re-licensed again in 1978, and I still have my call sign. WH6AED.

I built great ham equipment back then. Grounded Grids 811A's linears, 3 tube superhet reciever, a 12BY7/807 35 watt transmitter, and a mono quad loop antenna for 20 m. But as soon as I finish putting together my shack outside. I will be on the air again, this time as a QRP operator.

Ok., I am sending to you the 12AU7 phono preamp ckt. Its output is about 1volt. Feedng that into a line amp; should give a good smooth/warm tone output. A good 12AT7/12AX7 line amp would do handsomely.

This preamp is as simple and as clean as we could make it back then. Using the most cheapest parts. Since 12AU7's back in the 60's went for 79 to 85 cent new and far less used.

Some people used the 5814's and stated that it sounded better. But it is all up to the person listening to it.

The power supply uses two 220 volt pri. 12 volt/2amp sec. transformers, wired sec. to sec.. The transistors are MPSA42 and MJE13007. I used the MJE13007 because I used it so much in switching psu and linear converter.
But any high voltage transistors can be used. Even a TIP49/50.

Keep your wire runs tight. Use shield mic cable for signal paths and a good star ground.

Your S/N should be acceptable. And may even better if you are using a good cartridge. Good channel separation in your cartridge aids in S/N out come as well.

The ckt. is in CircuitMaker 2000 format.

Take Care


Ivey
Attached Files
File Type: doc 12AU7.doc (14.4 KB, 504 views)
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Old 11th January 2010, 05:51 PM   #29
Ivey is offline Ivey  United States
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Default EF86 schematic

Chris:

The EF86 schematic of the preamp. Is it the one from Audio Mag 1958/59 or the 1961 edition.

Also there is a similar one from Quad and Mullard. Thomas and Neel, friends of mine in England, helped design those. They are High gain units and very, very good. Also a German, designed one on the same profile.

In Hawaii, in 1973, I meet a Japanese gentlemen that design one on the same profile, using 6AU6's.

If it is the same profile, I would love to view it. To see if there are any changes or improvements worth noting.

Remember: all changes.., are not always improvements. Just changes.

But if you could post it. A O.K.

Take Care


Ivey
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Old 11th January 2010, 06:34 PM   #30
Ivey is offline Ivey  United States
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Default 5703wa/wb uhf tube

Ed:

My god.., you have those!!!

We used those in aircraft radios, 24 volt ac /400 hz converters, gyro units, and host of other things. First built by Tung Sol. They stop making them in 1974.

They are limited to about 120-150 volts for any good use. Even thou they are rated for more. About 2.5 watts out. A good triode.

First things first. Do you have the sockets? If not, then you can clamp them to a piece of aluminum standing up and hard wire them. Isolate the aluminum stand from the chassis, with mica. But place the tube direcetly to the aluminum for cooling.

A real good schematic for that tube is the Futterman NCP-1. Just do not overdrive the tube.

Do not overdrive them by designing to close their class a cut off limits, they distort ease. Ramp up the signal using multi stages; about three. No, try two at first. Maybe even cascode. Scope and listen to your output. Then use a line amp to complete the preamp profile

Take Care

Ivey.

Last edited by Ivey; 11th January 2010 at 06:39 PM. Reason: gammar
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