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JLH 10 Watt class A amplifier
JLH 10 Watt class A amplifier
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Old 8th January 2021, 03:52 PM   #7561
cogitech is offline cogitech  Canada
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JLH 10 Watt class A amplifier
Won't the same part numbers from the same manufacturer have approximately the same hFE vs. Ic curves?

If my goal is not to match, but only to determine which ones have greater gain than others, isn't a low power test accurate enough?

Anyway, I am glad to have an excuse to buy a tester. I bought this one, since I am happy with my basic DMM for other tasks. https://www.amazon.ca/gp/product/B084YRYXV5/

It is going to be very handy for quickly testing other components as well.
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Old 8th January 2021, 03:58 PM   #7562
cogitech is offline cogitech  Canada
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Quote:
Originally Posted by OldDIY View Post
1.Install the transistor on the heat sink
2.Take a power supply or 4-6v battery
3.Connect (-) batteries to the emitter
4.Connect a 470ohm resistor to the base, the other lead to the (+) battery
5.Connect a multimeter in current mode(10a) to collector and (+) battery. Write down the measurement number and current.
6. Take the next transistor (see 1)
At the end of the measurements, compare the obtained figures
Thanks! I was typing and missed this post.

I am going try this. I wanted that little tester anyway so I won't be cancelling the order but I am going to have fun playing with this test setup in the meantime.

One question: "Write down the measurement number and current." - If my DMM is in current mode, I am only going to get a current measurement. What other "measurement number" are you referring to?

Last edited by cogitech; 8th January 2021 at 04:05 PM.
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Old 8th January 2021, 04:07 PM   #7563
osscar is offline osscar  Latvia
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what kind of power supply are you planning?
from my experience - a 24V power supply at 1.1 -1.2 A with CRC approx. 25000uf 1R 25000uf for each channel - is enough to have less than 100uV ripple noise at the output.this is acceptable to me and can't be heard even with my ear at 93db speakers
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Old 8th January 2021, 04:11 PM   #7564
indra1 is offline indra1  Indonesia
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Mark the transistors with numbers and use that number as measurement number in your note.
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Old 8th January 2021, 04:21 PM   #7565
cogitech is offline cogitech  Canada
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Quote:
Originally Posted by osscar View Post
what kind of power supply are you planning?
from my experience - a 24V power supply at 1.1 -1.2 A with CRC approx. 25000uf 1R 25000uf for each channel - is enough to have less than 100uV ripple noise at the output.this is acceptable to me and can't be heard even with my ear at 93db speakers
I am going to use a 24V 4.5A Omron SMPS that I have sitting in a box doing nothing. If I am not happy with it during bench testing, then I will build a simple linear supply from scratch. I do have some 30,000uF 100v beer cans sitting doing nothing.

I know, I know - an SMPS for a JLH is crazy, but I wouldn't be the first to do it.

Last edited by cogitech; 8th January 2021 at 04:25 PM.
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Old 8th January 2021, 04:22 PM   #7566
cogitech is offline cogitech  Canada
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Quote:
Originally Posted by indra1 View Post
Mark the transistors with numbers and use that number as measurement number in your note.
Of course!
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Old 8th January 2021, 04:31 PM   #7567
OldDIY is offline OldDIY
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Quote:
Originally Posted by osscar View Post
what kind of power supply are you planning?
from my experience - a 24V power supply at 1.1 -1.2 A with CRC approx. 25000uf 1R 25000uf for each channel - is enough to have less than 100uV ripple noise at the output.this is acceptable to me and can't be heard even with my ear at 93db speakers
Can be reduced by applying (+)power separately to the collector of the upper output transistor and the rest of the circuit
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Old 8th January 2021, 05:49 PM   #7568
Alan Frobisher is offline Alan Frobisher
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No need to match o/p pair,as it is asymmetrical,one half is an emitter follower (upper),the other a grounded emitter. Later 2N3055s used the Epitaxial process , giving higher ft.,older ones used the Hometaxial process. A visit to "The Class A Amplifier Site" ,now hosted by Rod Elliott on the Elliott Sound Products web site,is well worth while. There is an update (Sept.1996) by the Great Man himself on improvements to the original design,plus constructors' personal experiences and improvements. If you intend to build a pair of amps. using your proposed transistors ,construct in such a way that the output transistors can be changed easily,in case the results are disappointing . Don't forget ,there have been massive advances in transistor technology ,with much better devices being available.I built a J.L-H. with Toshiba 2SC5200s*,the amp sounded far too "Bright",not surprising as the freq. response was still flat at 250 KHz.! Sanken make a widely used range of audio power transistors with multiple emitters ,worth considering.
* BEWARE OF FAKES! Buy from reputable dealers only!
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Old 8th January 2021, 06:15 PM   #7569
gpapag is offline gpapag  Greece
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Quote:
Originally Posted by Alan Frobisher View Post
Wonderful to see revived interest in J. L-H.'s design and that it has stood the test of time.
Simple designs are often the best!
This is how my JLH1969 built about 45-47 years ago measures today (I am in the process of verifying the performance of my amplifiers)
BC212 (Siemens), BC 140 (Siemens), 2N3055 (Motorola).
1uF MKT input, 470uF bootstrap, 2200uF output (capacitors are some 15 years old).
1 Ampere per channel at 24Vdc

George
Attached Images
File Type: png 1 JLH1969 FR100mW various loads.png (116.6 KB, 129 views)
File Type: png 2 correction of FR.png (97.4 KB, 128 views)
File Type: png 3 JLH1969 THD100mW various loads.png (169.2 KB, 132 views)
File Type: png 4 JLH1969 THDvsPower@4 Ohm.png (95.4 KB, 117 views)
File Type: png 5 JLH1969 THDvsPower@8 Ohm.png (96.0 KB, 116 views)
File Type: png 6 JLH1969 THDvsPower@16 Ohm.png (92.1 KB, 17 views)
File Type: jpg 7 JLH1969 50Hz THD 100mW@8 Ohm.jpg (115.5 KB, 23 views)
File Type: jpg 8 JLH1969 500Hz THD 100mW@8 Ohm.jpg (115.8 KB, 20 views)
File Type: jpg 9 JLH1969 5kHz THD 100mW@8 Ohm.jpg (116.5 KB, 17 views)
File Type: jpg 10 DSCN5636.JPG (647.0 KB, 65 views)
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Old 8th January 2021, 07:49 PM   #7570
mjona is offline mjona  New Zealand
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Reminds me of the 1969 JLH I built in a Hammond "Hamster Cage" made for valve amplifiers.
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