JLH 10 Watt class A amplifier

I could remove oscillations by shorting R1. R1 is in series with the input coupling capacitor (coupling capacitor is C1 on this board which is actually C4 in JLH's original schematic). I used some arbitrary (but low k) for R1 and apparently that is not required as per JLH! Before I can test it with speakers, I need to re-assemble the board that I was playing around with.
 
Join the team.

Hello! I will join the team.
Original Motorola 2N3773 is the output. (saved from old industrial power supply)
My test version schematic:
 

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Hello! It is currently in an experimental phase.
I haven’t measured it yet, I roughly calculated 4W music peak power.
I put it together quickly based on the circuit diagram.
It sounds good and 1.5W RMS is enough for me. I'll replace the transistor in it, that's all it was at home. :)
I'm sending some pictures:
 

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The 24Vac can be used with these transformers. Can be used up to 2.5A.
Voltage regulator is not a problem. LM317T (or 7824 (?)) with PNP power transistor.
I'm interested in the thing.
I have 6pcs 100VA 230V/30Vac hypersil transformer. 30Vac is too much, I can to make lower voltages.
 
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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
 
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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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.
 
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:
 

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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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