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Old 3rd July 2013, 04:55 PM   #1
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Question Please help with JLH for quad ESL radiators

Good evening dear colleagues,
As i am starting to collect parts for this wonderful amp i found myself in a dilemma. I have bought these two radiators from the picture attached and hoping to find some answers from you guys:
*Note that the dimensions for both of them are: L=25.5 cm; l=23.5cm; h (for the base)=1 cm. The dimensions for the fins are: L= 23.5cm and h=2.5 cm. The black radiator has one fin less than the other.
1. Are these results ok for the total dissipation area?
Abase=2(L*h+l*h+L*l) =>Abase is 648.25 square cm + 885 square cm for the total of 15 fins (from the formula Atot=L*l*Number of fins) => A=23.5*2.5*15?
The total dissipation area is, from the calculation above (for the black radiator) 1533 square cm?
2. Are these radiators suited for a stereo JLH for QUAD ESL at 42W@8Ohm , 3.2A quiescent current with 4 pieces 2n3055 per module?
3. Wich solution is best for the silver radiator: to spray it with a black thin coat of thermo resistant paint or to black anodise it (sollution wich i do not have at disposal in my county)?
Thanks in advance
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Old 3rd July 2013, 05:14 PM   #2
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The voltage for the amp wil be +- 28V CC.
Thanks.
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Old 3rd July 2013, 05:22 PM   #3
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I am thinking at ataching an aluminium L pad (with the output transistors) on the 1 cm base of the radiators and make a case with the radiators standing up.
What do you say?
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Old 3rd July 2013, 05:35 PM   #4
generg is offline generg  Germany
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Sergiu2009 I am afraid you are more competent in these things than me.....

If nobody answers here, hijack the Pass Forum open a thread,
I suppose you will get help!

Good luck!
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Old 3rd July 2013, 05:39 PM   #5
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Thanks generg. I have send allot of mp's to allot of colleagues that can help and i am hoping that they can help me and post here.
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Old 3rd July 2013, 06:02 PM   #6
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This is the schematic that i want to use on these radiators.
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Old 4th July 2013, 07:37 AM   #7
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If you paint a plain heatsink if some flat black enamel it will greatly increase its emissivity.

It is amazing that not only does black absorb heat well, But it also increases its ability to radiate it too more so than what just plain metal does!!

The reason to use Flat black is that it increases its surface area ever so slightly but every little bit helps.

Each amp will be dissipating about 180 watts of heat, per bank of output devices at 28v*3.2A=89.6 watts.

Your heatsinks may be a bit on the small side.
I think that the two of them may work for one amp if you choose not to use a fan.

I haven't built a JLH yet but I have been wanting to try it out sometime.
There are some very good threads on this design.
It seems that +/-28v is a bit high and I think that typically they run on just one 28v supply across both halves of the output devices ( I may be wrong on this).

If they run a bit hot you can always put a small fan on them.
You would be amazed on what just a little bit of air flow can do!!

But if you choose to not use a fan you need quite a bit more area in order to keep them from getting too hot.
I am guessing about 4 times as much!

Take a look at size of heat sinks that some of the Pass amps that many have made without using a fan, They're huge even for this power range.

A 12v fan run at 5V or so may be enough and will help to keep the noise down as well.
Keep in mind that if you mount them in a aluminium case this also helps to dissipate the heat as well (somewhat).

Here is a link of some great Heatsink calculators that I have found,

Another heat sink size question

The temps are in Kelvin but I also supply a link for a conversion calculator as well.

I think that they will work and you can always increase the air flow like I have suggested.
I have seen a few projects using similar sized heatsinks.

I will run the numbers for you and take a closer look, But I won't be back on for a a day or two, due to the 4th of July holiday tomorrow.

I was working on sim's on this design a while back and was interigued by its performance.
The design I had come up with was using 8 pairs of some cheap ole' Tip3055's at $.45 each per amp.

Many seem to like the JLH a lot!!!
It has a lot of performance for some old junk box parts.

I have a couple of large power transformers that I have been wanting to build some very large class A amps, But cooling of these amps is an is an issue for me as well.
I have been considering water cooling but I am going to start out small at first just to see if they are what they say they are.

What is your final impedance that you are planning on driving?
With 3.2Amps of bias current per halve this will supply 6.4 Amps P-P to the load for a Class A amplifier.

This is 81.92 watts peak (57.91 Watts RMS) into a 8 ohm load at 25.6Vpeak across the load.
This is a lot of power for a ClassA amplifier.
Hmmmm.......I guess 28V per rail would be in line for this!!

For 4 ohms it is half of the above figures as determined by ohms law, even though the amp will still be dissipating 180watts!

I may forgetting my numbers now, so I will brush up on this.

I am planning a bridge version as this will raise the efficiency from the typical 25% to 50%.
This allows you to run a 1.6 Amp bias and still be able to supply the load with 3.2 Amps of current (due to the doubling of the output voltage from being bridged).

Typically most JLH's are set up 1.6 to 2.8 amps or so, But again I am no expert on this matter.

I have found that increasing the number of output devices helps to increase it's performance as well due to better distribution of heat between the output devices.
This is why I had come up with using 8 pair of some cheap TIP3055's.

I don't have any of the more modern Quality output devices to work with at the moment, But, I have read many discussions on them and some seem to like the older ones better and some don't.

Anyhow I will be very interested in the outcome of your project!!
As it will inspire me even more to finally build one.

I have a few 2N3055's and 2N3772's around but they are tied up in my Sunn Concert Slave amps for my guitar rig.
Although, I can't use those amps now because I have to replace the aging bias resistors that get very hot now and start to smoke every time I fire them up!

Cheers and Good luck !!!

Jer

Last edited by geraldfryjr; 4th July 2013 at 07:42 AM.
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Old 4th July 2013, 10:09 AM   #8
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On painting the heatsink,

You want to keep the paint layer as thin as you can.

The object is to cover the material but not have a thick build up of paint.
If it is rough and sandy feeling this is good as this has a rougher surface and has the effect of increasing the surface area.

jer
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Old 4th July 2013, 10:42 AM   #9
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Sergiu,

I have heard that the JLH is not particularly good with an ESL; it has some instability at higher loads of capacitance due to phase shift.

The heatsinks are OK, but you really need to measure the thermal capacity and the quiescent current of the output current of each amp. Until we know the rating in C/W we cannot know how much the rise of temp.

The best topologies with highly reactive loads like ESLs are Class A tubes.

Cheers,

Hugh
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Old 4th July 2013, 11:29 AM   #10
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This is something I wish to explore.

The JLH is a simple Class A amp of yesteryear.
And when working with ESL's you must understand how the impedance curve works and how it effects the voltage output of the amplifier.

Most amps don't handle this very well but a Class A amp can do this very well with in its designed range of operation.

If the signal is out of phase by 90 degrees whether it be lag or lead due to the reactive components it requires the amp to maintiain nearly 5 to 6 times the current or voltage depending on lag or lead of the reactive component, to maintain the same power level.

This is why it takes a big amp that can deliver a large amounts of current to make the speakers produce what they have to produce to make the sound right.

But, When it comes to a purely capacitive load the extra current is a plus.
Since the current is leading, the amplifier has to supply larger amount of current at once.

This is only for the highest of frequency's.

This does not include the effect of the transformer except for its added (or Parasitic capacitance).
At the lower frequency's the transformer's inductance of the primary winding is what determine's the impedance that is presented to the amplifiers output and has no effect on the ability for the ESL to produce sound except for its surface area, as for all bass system's!

The ESL at this point has a very high impedance and the the voltage the it presented upon its stator's is what determines what position the diaphragm will be at.

I have full DC control over my ESL Diaphragms.
At a low frequency a capacitor has its highest impedance and it takes nearly zero current to make the diaphragm move.

To make bass you must have Displacement!

The Higher the frequency of operation you need more current, It works like this in the RF world too!!

jer

Last edited by geraldfryjr; 4th July 2013 at 11:42 AM.
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