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JLH 10 Watt class A amplifier
JLH 10 Watt class A amplifier
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Old 14th June 2021, 02:16 PM   #8071
sierratds is offline sierratds  Brazil
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Quote:
Originally Posted by hanair View Post
Have you followed the schematic exactly as shown in the following post?

JLH 1969 Explanation

I am building a JLH1969 on a new PCB using TTC5200 and noticed severe oscillation. I had to use 1.5nF between collector-base for both output transistors to get it working but that severely limits the bandwidth. I also substituted 2N4403 instead of 2N3906 and 2N4401 instead of 2N1711.

Hi Hanair, Yes, I am use this scheme. See my test in video:

TESTE #3 - Amplificador CLASSE A - JLH 1969 (10W) 25,5V DC - YouTube
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Old 14th June 2021, 02:42 PM   #8072
hanair is offline hanair  United States
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JLH 10 Watt class A amplifier
Oscillation issue is fixed, my board has an input resistor and I used some random value in the range of k ohms. It works fine with 100R or even shorted. All good now!
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Old 14th June 2021, 03:57 PM   #8073
bistvan1980 is offline bistvan1980  Hungary
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JLH 10 Watt class A amplifier
Quote:
Originally Posted by OldDIY View Post
MJE13007 can also be used at the output. For a driver, their characteristics are not quite suitable. But it will work)))
I replace the driver to 2SD882 and increase supply voltage(use lab PSU), current set to 1,3A(24Vdc):
https://www.st.com/resource/en/datasheet/2sd882.pdf
Great!
My objective: 24Vac to 24Vdc(stab.)... I'm on it.


Hi Sierratds and Hanair!
Good job!
I watched the video, now I know it's 1.2A enough. Thanks a lot!
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Old 15th June 2021, 12:06 PM   #8074
john_ellis is offline john_ellis  United Kingdom
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I would not recommend the 2N3773 for audio. At least, not without testing ft.
Old RCA spec ft(min)=200kHz. Maybe about the same as an OC71!
Moto's 2N3773's were made with a different process and today's 2N3773's will be epi base of some description and MAY have a better ft (around 2MHz) - but I don't have a 1981 era device to test. But the spec should disqualify as it is still 200kHz.
In the JLH the frequency response is not best aided with NFB because there is no additional drive current (e.g. from a driver transistor) to push the base current up when the gain falls. Yes it will improve at low output levels but full power at high (audio) frequencies is likely to have higher distortion.
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Old 15th June 2021, 12:54 PM   #8075
bistvan1980 is offline bistvan1980  Hungary
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JLH 10 Watt class A amplifier
Hi! Thanks for the reply!
Probably true. I'll buy 2SC5200s. (with 2SC2625 is better than 2N3773? - 2SC2625 is already at home)
Its sound is tolerable with 2N3773, I have not tested it at a volume higher than 2 Watts. (for other reasons)
I'm testing the 24V stabilizer now. PC-PSU heatsink is small for this (old S478 proc. cooler is better)
MJE13007 + MJE13009 darlington, BZX18V + 3xblue LED.
(I know the 7824 + PNP construction is better ...)
Some pictures:
Attached Images
File Type: jpg 01.jpg (290.7 KB, 293 views)
File Type: jpg 02.jpg (190.8 KB, 304 views)
File Type: jpg 03.jpg (324.0 KB, 294 views)

Last edited by bistvan1980; 15th June 2021 at 01:06 PM.
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Old 15th June 2021, 01:16 PM   #8076
OldDIY is offline OldDIY
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2N3773 are well suited for power supplies. 2SC2625 have low Hfe. Check yours at 12v at 1A (on heatsink).
You can use the capacitance multiplier circuit, but add a zener diode (previously suggested here).

Last edited by OldDIY; 15th June 2021 at 01:21 PM.
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Old 15th June 2021, 02:47 PM   #8077
john_ellis is offline john_ellis  United Kingdom
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2N3773 are well suited for power supplies-
yes, for which they are very good. And all I have ever used them for!
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Old 15th June 2021, 04:17 PM   #8078
bistvan1980 is offline bistvan1980  Hungary
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5200s in progress (waiting for shipping).
Until then; output transistors MJE 15028 (ONS)
https://www.onsemi.com/pdf/datasheet/mje15028-d.pdf
Temporarily I applied the stable 12V back. IQ = 0.9A.
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Old 17th June 2021, 03:20 AM   #8079
jbau is offline jbau  United States
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Quote:
Originally Posted by Mark Johnson View Post
I have a feeling what you REALLY want, is to gaze at the first attachment to post #2. Like most of the other plots, that one measures out better than the manufacturer's datasheet promises. Customer expectation management (?)
The 2SC2039's I received don't look quite as rosy as your plot. These are 0-20V sweeps, 1mA/div and 20mA/div. Hfe is over 400. Lots of looping at low Ib. Linear beta at a given Vce, but beta expands with Vce. If AC appears across CE, this will be a beta modulator.
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File Type: jpg 2sc2039-20.jpg (89.3 KB, 66 views)
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Old 17th June 2021, 07:58 AM   #8080
OldDIY is offline OldDIY
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MJE 15028 (ONS) - You can use parallel connection with resistors from 0.1 ohm in the emitter.
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