Another lamp replacement question

[euphemismos]

I recently had a SA-7500 integrated restored by a local tech and it is performing and sounding beautiful. As part of the restoration, the power lamp was replaced with a brand new non-LED (8v 50mA) lamp. This is the only lamp on the entire unit. After about 3 days it stopped working. The connection is still secure. Before I just replace it again, I'm wondering if maybe there could be something causing the lamp to blow. Any advice regarding what else I could check would be greatly appreciated.

 

[markthefixer]

The 8v 50mA lamp on the SA-7500 is run off of a rather high AC voltage that is tamed by R58 a 620 ohm 2 watt resistor.

That resistor would have needed recalculating if the current of the replacement lamp was significantly lower than 50mA.

50ma with 620 ohms is 31 volts
35mA on 620 ohms is 21volts
35mA and 31 volts needs 885 ohms or the bulb will get too much voltage,
the current will increase beyond the rating of of the lamp and premature burnout becomes a possibility.

Other units run the lamps off of an 8v transformer winding, and thus this will not occur because no dropping resistor is used or needed.

He should have measured the AC voltage developed across the burned out lamp, that would have given him a clue.
He needs to know that AC voltage, and the current of the lamp. subtract the lamp's voltage (8v) from THAT AC voltage reading across the dead lamp,
and divide that number by the lamp current for the number of ohms needed. wattage of the resistor is the subtracted number again times the current.
It will be less than 2 watts unless a higher current lamp was used.

Had a HIGHER current lamp been used (ABOVE 50mA), this would not have happened, as the lamp would just have been slightly dimmer.
But there are a LOT of lower current 8v lamps out there - the chances of getting one are pretty good.

 

[larryderouin]

I used to get my 200ma & 250ma 8v fuse lamps from www.wjoe.com in lots of 10. 8V 250ma is part # 202217 8V 200ma is part # 207269
Either are $0.90ea or 10 for $7.50.
Larry

 

[euphemismos]

The 8v 50mA lamp on the SA-7500 is run off of a rather high AC voltage that is tamed by R58 a 620 ohm 2 watt resistor.

That resistor would have needed recalculating if the current of the replacement lamp was significantly lower than 50mA.

50ma with 620 ohms is 31 volts
35mA on 620 ohms is 21volts
35mA and 31 volts needs 885 ohms or the bulb will get too much voltage,
the current will increase beyond the rating of of the lamp and premature burnout becomes a possibility.

Other units run the lamps off of an 8v transformer winding, and thus this will not occur because no dropping resistor is used or needed.

He should have measured the AC voltage developed across the burned out lamp, that would have given him a clue.
He needs to know that AC voltage, and the current of the lamp. subtract the lamp's voltage (8v) from THAT AC voltage reading across the dead lamp,
and divide that number by the lamp current for the number of ohms needed. wattage of the resistor is the subtracted number again times the current.
It will be less than 2 watts unless a higher current lamp was used.

Had a HIGHER current lamp been used (ABOVE 50mA), this would not have happened, as the lamp would just have been slightly dimmer.
But there are a LOT of lower current 8v lamps out there - the chances of getting one are pretty good.

Thanks for this information. The service manual designates 8v/30mA. I purchased and put in the 8v/50mA as a replacement. So if I understand correctly, what your saying is that it's possible that the lamp I purchased may have had a much lower current than advertised and subsequently only lasted a couple of days? Also, on the other hand, is it possible that the R58 is old and therefore not doing it's job (resulting in the lamp burning out)?

 

[larryderouin]

Actually there is a conundrum here. The exploded diagram on page 21 defines the lamp as a 8V30mA but the parts list(page 31) shows the same part # (AEL-023-0) as 8V 50mA. I would replace with another 8v50ma (this is a common value among Pioneer amps). Check R58 (out of circuit) for value. If out of spec, replace it with a new part.

 

[euphemismos]

Actually there is a conundrum here. The exploded diagram on page 21 defines the lamp as a 8V30mA but the parts list(page 31) shows the same part # (AEL-023-0) as 8V 50mA. I would replace with another 8v50ma (this is a common value among Pioneer amps). Check R58 (out of circuit) for value. If out of spec, replace it with a new part.

Yes. From what I can gather, the 8v 50mA is what I should use. I'm going to check the voltage after the R58 (going to the lamp) and out of circuit too. If that all checks out, then I guess it could be possible I had a faulty lamp.

There's a seller on ebay selling replacement LED lamps specifically for the SAxxxx line of amps. They have resisters installed in the shrink on the leads and supposedly can be dropped right in. Does anyone have any opinions on these? Seller says they are "bright white" and I'm wondering how drastic the brightness will be. It would be great to go with LED as long as it's not shooting a laser beam of light out of my amp. I know the color won't have the typical orange/amber hue, but since it's the only light on there, it might be okay.

 

[aldena007]

I have been replacing the OEM lamps in two SX-3800's with LED's and the lamps I bought off eBay work fine but they were very bright and I had to use some parchment paper to dim the LED's. The brightness was really distracting but on a power on indicator it may be OK. I use LED's for longevity and the fact they run much cooler but there are always adjustments required to duplicate the OEM look.