AUDIO RESEARCH SP-6A schematic

[dray177]

My ARC SP-6A need to be repaired :
- the first regulator Q1 ( a Motorola MJ410 ) is out and its emitter resistor ( located on its right ) is burned,
- I hope there is only that !

My problem to solve :
- I am unable to know ( due to smoky color codes ) the value of this burned resistor,
- my reading is 362 ohms, but I think it is wrong,
- If I consider SP-6 diagram this is a 1kohms carbon resisistor,
- but I don't know if this value is the same for my SP-6A.

Please, I need your help :
- the best for me would be to have SP-6A diagram,
- or possible to give me color codes on it if you know that.

Thanks to You,
Raymond


For you below, this Q1 regulator, and just on its right side the burned R :

An externally hosted image should be here but it was not working when we last tested it.

 

[Billc]

1K in the SP-6.

Bill

 

[dray177]

1K in the SP-6.
Bill

Thanks Bill for your interest !

- 1K for the SP-6, I know,
- but for the SP-6A, how much ?

Raymond

 

[leadfinger]

Hello Raymond,

You may find the info you need here; ARCDB.

Dave

 

[dray177]

You may find the info you need here; ARCDB.
Dave

Thanks Dave.

Of course I know.
But alas, there is no diagram for SP-6A !

Raymond

 

[SY]

Q1 in the SP6A is an MJ413. Q2 and Q3 are MJ410. Q1 doesn't have an emitter resistor, the emitter goes right to the collector of Q2, to an 18k resistor feeding a zener string (the voltage reference for Q2), and to a 1k8/1W resistor which is part of an RC filter. Q2 has an emitter resistor of 1k/1W. Q3 has an emitter resistor of 10k/1W.

Frankly, it's a very crude, low performance regulator. I'd replace it completely with a cheap Maida or a two transistor feedback regulator, either one using a MOSFET pass device.

 

[dray177]

Q1 in the SP6A is an MJ413... ...

Thanks SY for your explanation !!!
I just send you a message by e-mail.

Raymond