Information request for modifying Bose 401s

Good question!

I think I am correct in saying that at no point in the thread has SpineyNorman indicated he has a meter, let alone one that measures capacitance and ESR.

I have asked for resistance readings of protection lamp and series resistor - if only for the record. We'll see if they are forthcoming.

A good quality Nichicon NP electrolytic capacitor is fitted, but it is now 37 years old. However, a small departure from the original capacitance and ESR values may not be too significant in the context of this 1st order HF filter - so SpineyNorman may simply decide to leave it in circuit.

If it were me, I would put a fresh capacitor in as a matter of course - especially since I'd gone to all the trouble of opening up the loudspeaker.
I do have a multimeter and it can test capacitance. And I am still trying to locate a pair of suitable replacement caps. I do have a question regarding the official schematic and parts list @6thplanet provided a while back. It showed: C1 Capacitor, 5uf, 10%, Electrolytic. R1 Resistor, WW, 5 watts, .5 ohm.
Then a second line: C1 Capacitor, 4.5uf, 10%, Electrolytic. R1 Resistor, 5 watt, 10%, 1.0 ohm.
Am I to read correctly that the caps and resistors in the second line of C1 and R1 are suitable replacements should those in the first line be unavailable?
This is my soldering iron, I am concerned that it won't reach a high enough heat quickly to avoid damage to the terminals on the caps and resistors if I do change them.
Weller Soldering Iron
 
The exact value of capacitor will depend on the amount of resistance in series with it

Yours will be 5 uF to match the resistor and lamp fitted to your particular speaker.

Since you have a multimeter, why are you not telling me the resistance of each of these two components?

P.S. The gun should be alright if you solder quickly. You can also attach a crocodile clip between the component and its soldering point to act as a heatsink.
 
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And I am still trying to locate a pair of suitable replacement caps.

I don't know if you can get them over there, but Mundorf of Germany do a 5 uF Bipolar E-Cap.

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Am I to read correctly that the caps and resistors in the second line of C1 and R1 are suitable replacements should those in the first line be unavailable?

I'll try answering your question directly.

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To the best of my knowledge, 4.5 uF NP electrolytic capacitors are not obtainable, whereas 5.0 uF ones are.

A workable compromise in either scenario would be to employ the readily available value of 4.7 uF.

P.S. There is no need to replace the lamp and resistor if they are in working order, so be sure to measure their resistances and to carry out 6thplanet's tap test on the lamp. There are opinions that there is no need to replace the capacitor, but I suggest you could at least measure its capacitance.
 
It seems like this thread is taking a turn sui generis.

I believe the time has come to finally dare (that's, to act) because I understand perfectly that some objects can also have sentimental value, but they shouldn't exaggerate too much. IMHO

Some posters (including me) have asked for some easy tests to be done at zero cost, but they have not been done (yet) and it seems that replacing the capacitor is the only choice that will solve everything despite there being no evidence (yet) of this nor even the approval of the passive speaker repair tech for Bose in the USA.

I'm not an expert technician and not even a technician, but it seems to me like a matter of common sense and frankly it doesn't seem like the correct way to continue... IMO
 
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Just thinkin'..... that cap is worth more than the speakers.

Ha-ha! Your contribution indicates to me that this protracted thread is going viral! :D

I understand perfectly that some objects can also have sentimental value.

Very true, but there is unlikely to be sentimental value in this case since SpineyNorman picked the speakers up at an estate sale! ;)
 
Very true, but there is unlikely to be sentimental value in this case since SpineyNorman picked the speakers up at an estate sale! ;)
Nothing changes in the meaning of my post since it wasn't specifically said to the OP, but it was in my view the (only?) case that could justify a very simple thread of even over 110 replies without even seeing the path to the "conclusion" yet. ;)
 
Would you guys say that this capacitor is not the source of the problem?

The source of the problem likely lies with your non-matching tweeter combination. However the capacitor, resistor and protection lamp should be included as part of the trouble shooting regime.

What I can say is that if its equivalent series resistance (ESR) has increased from when it was new then the capacitor is a candidate for replacement.

Let's hope that when 6thplanet's tweeters are slotted into your system, your HF problems are instantly solved, making a capacitor substitution simply the icing on the cake!
 
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