Chilton QM3 capacitors

[eternal slang]

Hi,

I'd like to replace the 30-40 years old Philips electrolytics caps in a Chilton QM3 12 channel console.
I'll be using Panasonic FM and Nichicon HE including in the PSU.
Any other suggestions?

There are also two 2.2uf tantalum caps on the input module (C7, C44), a few other on the master card  and one 1uf on the PSU (C9), see schematic. Should I replace them, and if yes should I stick with tantalum or choose electrolytics substitues?

I'll share a mouser cart for those who would also like to do it as well.

Thanks for your help!

 

[JohnRoberts]

In the wayback machine, tantalum caps were use for their low impedance. Modern low impedance aluminum electrolytic caps (developed for switching supply applications) might be workable substations.

Perhaps try one channel and see what happens.

JR

 

[eternal slang]

Ok great, thanks for your help!
I'll try electrolytic substitutes on one channel and see if it works.

Of course with the same capacitance value, right?

 

[JohnRoberts]

Ok great, thanks for your help!
I'll try electrolytic substitutes on one channel and see if it works.

Of course with the same capacitance value, right?

yes, but specifically low Z aluminum electrolytic to replace tantalums, not general purpose aluminum electrolytic that are OK for replacing other general purpose caps.

The low Z caps may be cheap enough to use across the board, but not necessary for simple audio DC blocking. 

JR

 

[mjrippe]

Unless the tantalums are on power rails, I would leave them alone.  In an audio path they are unlikely to be stressed and fail or change value.

 

[analogguru]

And I bet, that this is just another chapter of the endless nonsense recapping-saga:

"Not a single electrolytic capacitor needed to be replaced and it didn't change anything (for the better)"

Why ?
Here is the answer:

At the left a (recycled) Philips electrolytic capacitor from 1976 and at the right a brand new (105°) electrolytic capacitor from 2019.

 

[JohnRoberts]

I routinely advise bench testing suspect channels to quantify and identify possible problems (but didn't this time, so here it is.)  8)

Typical evidence of old electrolytic capacitors deteriorating by losing electrolyte is low capacitance that can show up as weak LF response. A console provides numerous opportunities to benchmark channels vs each other. They are unlikely to all fail the same way at the same time.  If you identify a bad aluminum electrolytic, replace all same value parts as they likely same from the same production run.

Tantalums (on PS rails) often revel themselves as faulty by catching fire and releasing their smoke. 

JR

 

[eternal slang]

Thanks for all the wise advices!

Ok, thanks John, I'll conduct the tests you suggest .
But overall the console is fine and fully fonctional with nothing to worry about unless some crackling pots.
The idea was just to give it a few more happy years to go and not think about it anymore.

I would also be totally happy not changing them if I realize all is good and waiting until problems occurs.

Anyway, sorry to bring back again this nevrotic topic that has been beaten to death!!!

Fabien