I would not use a 20W 47 Ohm resistor to replace four 10W 10 Ohm resistors in series.

I would, however, use a 50 Watt 39 or 43 Ohm resistor if available.

 

I would not use a 20W 47 Ohm resistor to replace four 10W 10 Ohm resistors in series.

I would, however, use a 50 Watt 39 or 43 Ohm resistor if available.

Hello,
Unfortunately for me, neither 39 nor 43 Ohm resistor in 50watt version are available here.

 

Well, I do not know what you can get. Whatever you CAN get should measure around 40 Ohms, and be rated for at least 40 Watts.

 

Well, I do not know what you can get. Whatever you CAN get should measure around 40 Ohms, and be rated for at least 40 Watts.

Considering your below quote, i thought that the resistance between 40 to 70 Ohms is OK, so i found out that 47 Ohm 20 Watt Resistor. these Big resistors are difficult to find here. We have this Russian 10 Ohm 8 watt 1% resistor here but it is unusually big and arranging it in Series is practically impossible on the PCB board i have built.

You can increase the 10-ohm resistors to 15 to 18 Ohms if you would like.

 

Well, I do not know what you can get. Whatever you CAN get should measure around 40 Ohms, and be rated for at least 40 Watts.

Tried... Just cannot find 40 Ohm 40 Watt Resistor.
The only options available to me are as mentioned below
1) 4 x CRL-5W 10 Ом 5% (This is as per the original design)
2) 2 x SQP-10W 20 Ом 5%

Which one of the above is well suited?

I have built the pcb Soldered all the parts, only component remaining are the power resistors, I hope to finalize this project after this quote.

Best Regards

 

OK.
Get six more of the 20 Ohm 10W resistors.
Connect them together two at a time in parallel. Then connect the four groups of resistor pairs together in a series string.

Connecting two 20 Ohm 10W resistors in parallel makes a 10 Ohm 20W resistor.
Connecting four of those 10 Ohm 20W resistors in series makes a 40 Ohm 80W resistor.

Keep in mind that the original circuit was designed to be operated with 120VAC 60Hz in. You will be using 220VAC 50Hz in; nearly twice as much as it was designed for.

The initial load of the capacitor(s) will "look like" a dead short to the input for a few moments. There will only be these resistors to limit the mains power surge. 220VAC / 40 Ohms = 5.5 Amperes; almost exactly what your intended load is.
5.5A * 220V = 1210 Watts. That is a lot of power to dissipate, even though it is only for a short amount of time.
The original mains being 120V, same resistance, you would instead get:
120v / 40 Ohms = 3A; 3A * 120V = 360 Watts.
1210W / 360W = 3.36 times as much power to dissipate in this circuit than there was in the 120v circuit.

So, if you follow the instructions to use four pairs of 20 Ohm resistors in series, you will wind up with an 80 Watt 40 Ohm resistor, instead of a 20 Watt 40 Ohm resistor. This new resistor will have four times the power rating of the original, which should work just fine.

 

OK.
Get six more of the 20 Ohm 10W resistors.
Connect them together two at a time in parallel. Then connect the four groups of resistor pairs together in a series string.

Connecting two 20 Ohm 10W resistors in parallel makes a 10 Ohm 20W resistor.
Connecting four of those 10 Ohm 20W resistors in series makes a 40 Ohm 80W resistor.

Thank you for your useful reply, but i have one question though, what possible problems am i looking at if the the Wattage of my total resistor arrangement is 20 Watts, say for example i make the arrangement as "4 x CRL-5W 10 Ом 5%" OR "2 x SQP-10W 20 Ом 5". Will the Resistors over Heat and Blow off?

*Plz Note: The original design has 4 x 10Ohm (5 watts) Resistors in series.

 

I know what the original circuit has; as you thoughtfully provided the schematic in the first post.

You can try it with the total 20W rated resistors if you wish, but they will most likely get fried (burn up), and may damage your PCB in the process.

 

I know what the original circuit has; as you thoughtfully provided the schematic in the first post.

You can try it with the total 20W rated resistors if you wish, but they will most likely get fried (burn up), and may damage your PCB in the process.

Thank you for your reply,
I will go with your recommendation of making a 40 Ohm 80 Watt Resistor.

By the way, Is it ok to super glue the resistors on the chassis of my amplifier since there ain't enough space on the pcb to place or solder 8 resistors.

 

I don't know what your chassis is made out of. If it is metal, it would help to carry away the heat. If non-metal, it would tend to thermally insulate.

 

I don't know what your chassis is made out of. If it is metal, it would help to carry away the heat. If non-metal, it would tend to thermally insulate.

Hello,
Today i managed to find these soviet made resistors 20 Ohm 50 Watts, Bought two of them, will connect in series to make 40Ohm 100Watt and fly wire them to the soft start board and test.