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Old 12th May 2012, 06:58 AM   #2461
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Look, just a question "out of left field" re: temperature of heat sinks. Is there a cheapish way of taking an infra-red photograph (or other method) of a heat sink. RS and others stock packets of temperature sensitive paper strips that can be stuck to a surface and indicate a value but I was just curious if there is a more elegant version that gives a "picture" of what is going on. My current JLH is adequately "sinked" but I am contemplating fabricating half a dozen h/sinks for further versions and want a way of effectively checking them......other than the classic: "if it burns you then its not big enough" method.
Any thoughts. Cheers Jonathan
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Old 12th May 2012, 07:11 AM   #2462
mikelm is offline mikelm  England
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Quite a few DMM's that are half decent type K thermocouple socket and temperature probe - if you wedge the probe in between 2 of the fins with a suitably sized piece of cable you can monitor easily over a long period.

Perhaps even better would be a temperature data logger with a thermocouple socket - this way you don't have to watch it constantly and you can download a permanent record to your PC.

I don't know about IR temperature reading.
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Old 12th May 2012, 07:20 AM   #2463
mikelm is offline mikelm  England
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P.S.

check this out:

eSecure - Digital Cooking Probe Thermometer for Food, Meat, BBQ, Turkey: Amazon.co.uk: Kitchen & Home

there are others also - some less than £5
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Old 12th May 2012, 08:19 AM   #2464
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Thanks mikelm. Both useful. The other thing I thought about was one of those temp' sensing semi's bonded to each h/sink and a rotary switch (of the appropriate number) so as to switch each one to a single circuit/display unit. Bit like the old valve amp' voltage reading/monitoring system.
Cheers, J. To be continued...........
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Old 12th May 2012, 10:25 AM   #2465
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Quote:
Originally Posted by philpoole View Post
Sorry, I meant,perhaps he would of proposed a cfp phase splitter in his '96 variant - if he thought it would have been of benefit. And why not CFPs on the output stages?
If I recall, he also suggested Hiraga-esque phase splitters as an improvement somewhere else in his book.
I really like the fact that the JLH class A is a very stable amp - partly because there are very few stages in it, adding phase.

However, I think it might be interesting to investigate a variation of the 2000 version, perhaps with CFP phase splitter one day. I'm convinced I don't need much power (I think 10-15W is too much), so might consider a new build one day - but it will have to wait (I have a few projects stacking up at the mo).
Correct, the cfp is only the least complex improvement he showed, not that the others are much more. There are more improvements that he shows in his book and I have another 2 sent to me via private contact when I was still a student. If you look at a sim youll notice how much closer the collector and emiter currents are when in cfp mode.

Where can I see the 2000 version ?? His design or someones mods ??
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Old 12th May 2012, 10:35 AM   #2466
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Originally Posted by mikelm View Post
I find it a bit odd that this CFP idea is dismissed just through a process of mental reasoning. I'm surprised that someone who has a self built "simple class A" isn't just a little curious about how it might sound.

On the other hand Homemodder, if you are that curious I guess the onus is on you to try it - it's the only way to really know how it would sound.
Im more curious is how others will like it, I played around with these circuits as a student more than 20 years ago. The last and best sounding was a circuit very similar that you see in SSA thread and in class A without feedback in output. This scheme was also developed with input from JLH to reduce high order harmonics, he was the original designer after all. Ive dumped all Class A design however, too much heat for so little improvement compared to well designed class AB.
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Old 12th May 2012, 02:43 PM   #2467
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the '2000 version' isn't an original JLH - it's on the jlh class a website. Basically a dual rail amp with CCSs to set the bias and offset. I think it's based on the '69 and not the '96.
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Old 12th May 2012, 02:46 PM   #2468
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The Class-A Amplifier Site - JLH Class-A Update
Maybe not 2000, but from around that time (I'm sure I've heard it referred to as that). Also, it's actually based on the '96. I knew what I meant!
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Old 12th May 2012, 04:33 PM   #2469
AndrewT is offline AndrewT  Scotland
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Which JLH book are you referring to?
I have 2nd edition, The art of Linear Electronics.
He only mentions the 15W ClassA '96 version from the Wireless World article and shows the 10W ClassA '69 version schematic.
There is no discussion of CFP, nor Liniac, nor any other modifications to his 69/96 ClassA amplifier.
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Old 12th May 2012, 06:57 PM   #2470
Bigun is offline Bigun  Canada
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Originally Posted by homemodder View Post
Ive dumped all Class A design however, too much heat
yeah, but you do live in one of the nicest and warmest countries my friend whereas I appreciate a bit of warmth in the winter.
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