three legs caps and other questions..

kyrochan · 17th June 2006, 09:55 AM

I should replace the big electrolytics in my guitar amplifier but I discover it use huge caps with three pins (with a triangular configuration) all pins are soldered, could I use standard two pins instead wich is the correct way of solder it???
Also in series with the speaker there's a parallel of two resistor of 4.7Kohm rated for 5W each (the amp is 50watt) putted here by some tecnichian or so... they are the big white square type of ones used in Xover, what do You think about?

Groundloops · 17th June 2006, 12:31 PM

There are electrolytics with three pins where the third pin is only for mounting on pcb, means it has no electrical connection.
And there are others where are two pins for + and one for -, so those are two caps in one package. Mostly to be found in older gear of the 70´s.

In the first case you can use any cap of equal or higher voltage and equal capacitance, a higher capacitance can be used if the caps are part of the psu.

In the second case you would need two caps with the above characteristics and tie the - pins together.

A circuit drawing or a photo would make things clearer ...

kyrochan · 17th June 2006, 02:03 PM

This is a little italian vintage amplifier, if I remind well the center pin of each electolytic is connected at the same part so I think it's for a sort of caps shielding (since the caps have a alluminium shield) and the two caps are connected in series for the standard PSU configuration: V+ - 0 - V-

Late I will post a photo of the PCB, hope this helps...
No idea above the 2.35Kohm resistor in series with the load it's a common configuration?

Groundloops · 17th June 2006, 02:47 PM

The resistors are absolutely uncommon. Maybe someone added them as kinda short-circuit protection. Such a big resistor in series (and with nothing parallel to it) to the speaker does nothing than increasing damping factor and output. What is the minimum impedance rating of the amp?

kyrochan · 18th June 2006, 06:20 AM

4 Ohm

Groundloops · 18th June 2006, 12:18 PM

Weird thing. I have no idea what purpose the Rs could have. I´d throw them out.

kubeek · 19th June 2006, 01:19 PM

notice they are in prallel, not in series. I guess it is some kind of dummy load.

Groundloops · 19th June 2006, 01:35 PM

Quote:

Originally posted by kubeek
notice they are in prallel, not in series. I guess it is some kind of dummy load.

Oops ! Right you are, he wrote of parallel, not series ...
So I follow your opinion.

17th June 2006, 09:55 AM	#1
kyrochan diyAudio Member Join Date: Jan 2005 Location: Bari	three legs caps and other questions.. I should replace the big electrolytics in my guitar amplifier but I discover it use huge caps with three pins (with a triangular configuration) all pins are soldered, could I use standard two pins instead wich is the correct way of solder it??? Also in series with the speaker there's a parallel of two resistor of 4.7Kohm rated for 5W each (the amp is 50watt) putted here by some tecnichian or so... they are the big white square type of ones used in Xover, what do You think about?

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17th June 2006, 12:31 PM	#2
Groundloops diyAudio Member Join Date: May 2004 Location: Hamburg / Northern Germany	There are electrolytics with three pins where the third pin is only for mounting on pcb, means it has no electrical connection. And there are others where are two pins for + and one for -, so those are two caps in one package. Mostly to be found in older gear of the 70´s. In the first case you can use any cap of equal or higher voltage and equal capacitance, a higher capacitance can be used if the caps are part of the psu. In the second case you would need two caps with the above characteristics and tie the - pins together. A circuit drawing or a photo would make things clearer ...

17th June 2006, 02:03 PM	#3
kyrochan diyAudio Member Join Date: Jan 2005 Location: Bari	This is a little italian vintage amplifier, if I remind well the center pin of each electolytic is connected at the same part so I think it's for a sort of caps shielding (since the caps have a alluminium shield) and the two caps are connected in series for the standard PSU configuration: V+ - 0 - V- Late I will post a photo of the PCB, hope this helps... No idea above the 2.35Kohm resistor in series with the load it's a common configuration?

17th June 2006, 02:47 PM	#4
Groundloops diyAudio Member Join Date: May 2004 Location: Hamburg / Northern Germany	The resistors are absolutely uncommon. Maybe someone added them as kinda short-circuit protection. Such a big resistor in series (and with nothing parallel to it) to the speaker does nothing than increasing damping factor and output. What is the minimum impedance rating of the amp?

18th June 2006, 06:20 AM	#5
kyrochan diyAudio Member Join Date: Jan 2005 Location: Bari	4 Ohm

18th June 2006, 12:18 PM	#6
Groundloops diyAudio Member Join Date: May 2004 Location: Hamburg / Northern Germany	Weird thing. I have no idea what purpose the Rs could have. I´d throw them out.

19th June 2006, 01:19 PM	#7
kubeek diyAudio Member Join Date: Dec 2005 Location: Prague, Czech Rep	notice they are in prallel, not in series. I guess it is some kind of dummy load.