LM334Z Discontinued

for Dynaco Mark II/III/IV and DIY PP monoblocks

LM334Z Discontinued

Postby jukingeo » Thu Jul 30, 2009 11:41 am

Hello all,

Just got back from ordering from Mouser, the LM334Z Temp comp used on the Poseidon board is discontinued.

The replacement for the LM334Z is the LM334D, which is a surface mount device. (The LM234Z is also discontinued)

Any suggestions as to an alternative leaded device?

Also another question, how necessary is this part? Could it be subbed for a cathode resistor or LED?

Thanx,

Geo
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Postby Ty_Bower » Thu Jul 30, 2009 12:16 pm

I wonder if either of these would work?

689-HV9921N3-G
689-HV9922N3-G

Or maybe this is a better choice?

689-CL2N3-G

...no, all these are no good. They're fixed current (20 mA). Assuming my math is correct, the Poseidon board is setup for 6 mA through the regulator.

Digi-Key has the LM334Z. I put ten in my order, and it said zero on backorder. If you're desperate, I suppose you could place an order from them.
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Postby mesherm » Thu Jul 30, 2009 1:38 pm

I have about a dozen or so LM234Z in my parts box.
If you just need a couple I can mail them to you.
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Postby Geek » Thu Jul 30, 2009 4:42 pm

Digikey still has them. Part # LM334ZNS-ND

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Postby jukingeo » Fri Jul 31, 2009 9:17 am

Geek wrote:Digikey still has them. Part # LM334ZNS-ND

Cheers!


I was on the phone ordering with Mouser at the time, so I went with the LM334D which is supposedly the same but in an SMT 8 pin package. I have not looked up the details on this as of yet though. I will do an in depth comparison of the 'D' as compared to the "Z". If there is no difference (electronically) then I will stick with it. I just will solder leads to the necessary 3 terminals and cut the rest of the pins off.

Now the only other consideration is this: Does the LM334 need to be located anywhere specific on the amp? I am assuming the 15 ohm resistor that parallels it should be near or next to the chip right? After all the LM334 is a temperature compensator. But that is just a guess.

Thanx,

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Postby Ty_Bower » Fri Jul 31, 2009 9:44 am

In Shannon's Eiclone, Poseidon and ST70 circuits the LM334Z is used as a constant current source. Allow me to quote a section from the Eiclone manual:

February 11, 2005

Overview
Starting with the Ike Rev B boards, footprints were added to incorporate a simple but effective constant current sink using the LM334Z, which needs only a single resistor to set the current.

The datasheet is here:
http://cache.national.com/ds/LM/LM134.pdf

Theory
References to using this device include ‘Valve Amplifiers’ by Morgan Jones, 3rd ed, page 140 and ‘The Art of the Electronics’ by Horowitz & Hill, 2nd ed, page 355 (brief mention). Both books mention caveats to this device. Jones warns of overload conditions which can cause the LM334 to drop below its ‘turn on’ voltage causing oscillation. AOE bemoans the temperature sensitivity which in turn lets it be used as a precision thermometer. Neither of these should cause any problem in our use, however. The previous stage is AC-coupled, so we shouldn’t expect a weird DC gate bias wreaking havoc on the long tail bias.

As for temperature, if the part starts at room temperature at 20C (68F) then got as hot as 55C (131F – in the range of a hot transformer and not likely), the change would be:

.000227V*293K/10 ohms = 6.7mA (20C = 293 Kelvin)

…versus

.000227V*328K/10 ohms = 7.4mA (55C = 328 Kelvin)

This is the type of deviation you could see normally with cold tubes and fluctuating line voltage, and this is an extreme example as the max temp will be much lower and near static after the amp warms up.


The "Applications Hints" section of the datasheet (page 5) also has some interesting notes.
"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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Re: LM334Z Discontinued

Postby Brik » Fri Jul 31, 2009 10:52 am

jukingeo wrote:The replacement for the LM334Z is the LM334D, which is a surface mount device. (The LM234Z is also discontinued)

Any suggestions as to an alternative leaded device?

Also another question, how necessary is this part? Could it be subbed for a cathode resistor or LED?


You could use the LM317L instead, although you'll be operating the device at the bottom range of reliable regulation.
(Minimum Load Current to Maintain Regulation Typ=1.5mA, Max=2.5mA)
    Current Set Resistor Value = 1.25V / 0.0076A = 163 Ohms
Assuming the combined cathode current of 7.6mA, you can use a current set resistor valued at 163 Ohms.

I would not recommend replacing the LM334 with a resistor for the following reason.
Given the specified voltage of 10V at the common cathode with 7.6mV through it, the tail-cathode bias resistor value would have been:
    Cathode-Tail Resistor = 10V / 0.0076A = ~1.3K Ohms

At 1.3K Ohms, the "tail" is too short for the long-tail-pair. :))

/B
Last edited by Brik on Fri Jul 31, 2009 9:39 pm, edited 1 time in total.
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Postby EWBrown » Fri Jul 31, 2009 2:36 pm

Check Jameco, they have them, or at least they had them a few months ago, and they tend to carry parts which have become obsolete.

An LM317 could be used, just observe the voltage delta between input and output / adjust, it should not exceed 37 VDC> A better alternative is the Ixys IXCP 10M45S, they're good for up to 450VDC, and can handle current, so they are also good for power tube cathode current regulators.

If you need higher voltage, there is anso an IXYS IXCP 10M90S which has a 900 VDC rating.

Lor lower current and voltages, try the TL431, it is intended as a shunt regulator, but it can also serve as a cathod ecurrent regulator, for small signal VA tubes - The Bottlehead Paramountuses two of these for each channel, one as a cathode bias for the 12AT7 input stage, and the other one controls a 300VDC shunt regulator for the same stage.

HTH

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Postby mesherm » Fri Jul 31, 2009 2:48 pm

A TL783 three-terminal regulator will work just fine as a CCS and it has a max voltage rating of 125 volts.
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Postby jukingeo » Fri Jul 31, 2009 4:32 pm

Ok, so in the context of this circuit, the temperature compensator is used as a current source. So then it isn't 'compensating for temperature' at all then?

Thus in essence it is like acting like the top tube in an SRPP circuit, correct?

Well, we will see what happens. If I find the LM334D's to cumbersome to use then I will seek out a different alternative or different source to get the original LM334Z

Another question: I never played around with using a 'silicon' current source before. How does it affect the sound considering that it IS in the signal path of both triode halves.

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Postby mesherm » Sat Aug 01, 2009 12:54 am

Actually the signal never passes through the CCS. If you put a scope across the CCS you see a DC voltage only. The signal path is forced to alternate between the the two triodes and their plate resistors. That's the beauty of it. (y)
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LM334Z

Postby Wiesiek Lipowski » Sat Aug 01, 2009 2:00 am

Can I use LM334 instead of LM334Z here? What's the difference between them?

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Postby Ty_Bower » Sat Aug 01, 2009 6:22 am

I don't think there is such a thing as an LM334 with no designation on the end. They all have some letter there to indicate the packaging.

http://www.national.com/mpf/LM/LM334.html#Availability
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Postby Writer Frog » Sat Aug 01, 2009 11:57 am

jukingeo wrote:Well, we will see what happens. If I find the LM334D's to cumbersome to use then I will seek out a different alternative or different source to get the original LM334Z

Be careful. These surface mount type devices may not survive an extended contact with a soldering iron. =:o

Theoretically speaking, the CCS is *NOT* in the signal path. It enforces the symmetry of the LTP inverter output while keeping the tubes at the optimal operating point.

The use of the solid state CCS should give you lower distortion.
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Re: LM334Z

Postby jukingeo » Sat Aug 01, 2009 3:52 pm

Wiesiek Lipowski wrote:Can I use LM334 instead of LM334Z here? What's the difference between them?

Greetings


This is the problem that I ran into. I have not seen JUST an LM334. It always had some kind of letter suffix on it and that suffix usually is the type of package design.

I am pretty sure my LM334D will function the same way as the "z", but instead of a 3 lead TO92 device, it is an 8 pin SO8 SMT package.

Here, take a look:

http://pdf1.alldatasheet.com/datasheet- ... M334D.html

As you see 5 of the pins are not used. I will just cut them off and attach longer lead wires to the needed 3 leads. So that is no biggie.

Writer Frog wrote:Be careful. These surface mount type devices may not survive an extended contact with a soldering iron. =:o


I am an experienced tech, so that will not be an issue.

Theoretically speaking, the CCS is *NOT* in the signal path. It enforces the symmetry of the LTP inverter output while keeping the tubes at the optimal operating point.

The use of the solid state CCS should give you lower distortion.


I never delved too deep into the use of a CCS. The closest I been exposed to one, is in the use of SRPP pre-amp stages.

Well, it is nice to know the LM334 doesn't affect the audio signal. In the past I always had qualms about using 'sand' in my tube circuits. Lately I haven't been as picky when it comes to silicon rectifiers and in this case I am willing to give it a shot. As long as the signal doesn't go through it and hence is 'degraded' by it, I am good :).

Thanx,
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