JLH 1969 amplifier detailed setup

Here are the instructions to assembly and setup 

Component list 

1	220uF 50V	C1	Electrolytic 470uF 50V also can be used
2	4700u 25V	C2	Use a good brand as this is in audio path
3	220 uF 50V	C3	Electrolytic 470uF 50V also can be used
4	0.47uF	C4	Film Capcitor above 100V use mkpif available
5	100uF 50V	C6	Electrolytic
6	input	J1	Vertical Mount Spade - PCB Tab Terminal 6.35mm Mal
7	SPADE	P4,P5	Vertical Mount Spade - PCB Tab Terminal 6.35mm Mal
8	Spk	P6	Vertical Mount Spade - PCB Tab Terminal 6.35mm Mal
9	2N3906	Q1
10	BD139	Q2
11	100r .5w	R1
12	560 1w	R2
13	2.7k .25W	R3
14	220 r .25w	R4
15	100k .25W	R6
16	8.2k .25w	R7
17	39k .25W	R8
18	2.2K .5w	R9
19	TIP3055	U1,U2	2n3055 ( original bel or cdil dupe may degrade quality
20	200k	VR1	RM065 or 3386P type 200k preset (204 marking )

Upgrades 

C1 C3 470uf 50V 

C4 use good quality film capacitor like vishay or audio grade mkp 

vishay 

bevenbi

C2 must be of good quality as its in the audio path .

There are lot of duplicates in the market so make sure you buy from a genuine dealer .

U1 U2 are the output transistors 2n3055 is a good choice if you get original CDIL or BEL ( market is flooded with duplicates so buy from a genuine dealer ). 

MJ15003 may provide better sound quality but its very costly compared to 2n3055.

CRC power supply 

1	4700uF 35V	C1,C2,C3,C4,C5,C6,C7,C8	8
2	DC+	P1	1
3	DC-	P2	1
4	DC + OUT	P3	1
5	DC - OUT	P4	1
6	spk rtn	P5	1
7	2.2 r 5w	R1,R2,R3,R4	4
8	4k7 2W	R5	1
9	2k2 0.5 w	R6	1
10	100nF 100V	U1,U3	2
11	10nf 100V	U2,U4	2
12	LED 5MM GREEN	U5	1

Transformer 

High Voltage Warning: Prioritize Safety for a Successful Project

Electrical projects offer a rewarding opportunity to learn and create. However, working with high voltage poses serious risks. To ensure a safe and successful project, prioritizing safety is paramount.

Unplug all equipment before any disassembly or modification. Even seemingly inactive components can retain a charge. When working with unfamiliar circuits, consult a qualified electrician to avoid potential hazards.

Always respect high voltage warnings. These labels are not mere suggestions; they highlight potentially dangerous components. By prioritizing safety, you can avoid injury and ensure a successful and enjoyable project.

For 8ohm speakers 

Use  two 20 -0  ac secondary transformers  4A each . Or one dual secondary transformer with each secondary 20 -0 4 amp ( total 8 amp ) note that its not the center tapped type ,

For other loads ;ole 4 ohm transformer has to be changed to get rail voltage as per this chart for example you have to use 12V transformer for 4 ohm loads 

Assembly 

Install resistor first , then spades and rest of the components you can watch this video to get an idea 

Heat sinks 

JLH is a class A amplifier and it will emit  80 percentage of electricity given  as heat.  You need huge heat sinks to run it cooler without damaging output transistors . 

http://www.perfectmetal.in/heat-sinks.html

Check profiles like N9  N56 N59  10 to 15 cm length of that profiles will be around 2KG that will be sufficient for one channel . Make sure that heat sinks have vertical fins you can use lower sized heat sinks if you provide active cooling with a fan .

As Rod Elliot quotes in his website  'there is no such thing as a heat sink that is too big' so dont try to save money on heat sinks . never operate the amp without heat sinks as that may damage , for very short term test you can use smaller heat sinks but connect a sufficient sized heat sink for longer operation . 

You can buy a temperature sensor and attach it to the heat sink for monitoring temperature during tests

 

Connections 

First power up 

After soldering components  make the connections as per above image.  Connect a 60w light  bulb in series to the primary of the transformer . Switch the power supply on,  if the light bulb is glowing very bright turn the power off immediately . There is a short somewhere on the board or wiring  . Check the board and see if any wrong connections are made , make sure the transistors are in right orientation .

Midpoint Setup 

Initially do not connect the speakers . Measure the rail voltage make sure its not above 28V  . If you use the above said transformer and CRC  supply you will get around 25 to 26 V , connect the a multi meter between +ve of the out put capacitor (4700uf ) and ground  (if its not accessible connect the DMM to u2 transistors  legs as in  this image. Turn the preset to set the voltage shown to half of rail voltage. If the rail voltage is 26 set midpoint voltage to 13V .

Biasing 

 Remove the light bulb and connect the transformer direct to the mains . 

Connect a DMM  between +ve out of CRC supply and amplifier boards  +ve in series. If your DMM requires to connect probes in different socket do that you may have to use the ten A socket for the probe in most of the multi meters  . Select current measurement mode( 10A) and check 

the current it should read around 1 A ,  1.2A bias is ideal for 8ohm loads . If its very less change the value of R2 to one step lower   like 510 ohms and measure again . If not reached the required biasing lower R2   to 470 ohm . Make sure you dont have the light bulb in series to transformer while bias test  . Once the current is around 1 to 1.2 A  Run the amplifier for half an hour then do the measurement again readjust the R2 if required .

Yellow DMM shows Bias current 930mA 

Red DMM shows supply voltage 

White device shows temperature of heatsink 

If 4 ohm speakers are used you have to change both R1 and R2 and do the sames steps again bias current and rail voltage has to be different like in this chart . 

Speaker selection also is critical use hi sensitivity speakers for good volumes . Hi q full rangers and tankband full rangers pairs nice with this amp.  

For PCB contact +91 85470 56859 (only whatsapp)

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