What are the 'actual' effects of old electrolytics in a vintage radio?

[Crystaleyes]

Hi all.

Just trying to get a better understanding of electronics in general, and although I know that it can be general practice to replace any electrolytics in vintage gear, I was wondering 'what' are the effects from these failed components?

I can see that a shorted cap acts as a short circuit and therefore a power drain, but what else might it cause?

Similarly, an open cap won't be smoothing any signals but is there anything else?


I'm sure this is basic 101 but I'm not at school, so just learning as I blow things up...

Fortunately I'm blowing lots of things up

[andrewsawesomr]

From what I've seen, failing or failed Electrolytic capacitors can cause low or no audio output from the speaker.

[Crystaleyes]

Welcome to the forum

Thanks for that. I suppose I should expect that from caps which are failing towards shorting.

[lti]

There are also caps in series with the audio signal, and those failing open or with high ESR would cause low audio. If they fail shorted or leaky, then they won't block DC anymore.

I've also had bad caps cause stuff to sound really strange (like distorted sound with weak bass).

[Crystaleyes]

Cheers.
I have repaired various easy-fix failed amps but as it is not my 'thing', I have never given it much tought.
It only just dawned on me that it should be indicative from the symptoms as to what kind of capacitor fault is the cause.

It's all helping

[Per Hansson]

The easy one is "mains hum" (50/60Hz) heard through the speakers when the big filtering capacitors are failing.
You can also have failure of frequency filters like in my post here, then it may make really really bad noises as lti said above:
https://www.badcaps.net/forum/showthread.php?t=93004

[Crystaleyes]

Thanks for the info, but here's another question...

There is the mains hum and all the caps have been changed. The two large outputs were originally 1000µF 25v and were replaced with 2200µF instead.

Could this extra value be creating the mains hum?

As a sidenote, only one channel is currently working, the other has a short, which as it turns out was the reason for the initial lack of volume.
Before that channel was isolated, there was no hum...

I suppose I'll find out soon enough once I find the short...

[keeney123]

Originally Posted by Crystaleyes

Thanks for the info, but here's another question...

There is the mains hum and all the caps have been changed. The two large outputs were originally 1000µF 25v and were replaced with 2200µF instead.

Could this extra value be creating the mains hum?

As a sidenote, only one channel is currently working, the other has a short, which as it turns out was the reason for the initial lack of volume.
Before that channel was isolated, there was no hum...

I suppose I'll find out soon enough once I find the short...

This article is good at explain twisted pair and why they are use.

https://audiouniversityonline.com/twisted-pairs/

When I work for UMass I remember one of the professors showing me how to twist a pair of wires for a 100MHz ring counter that was used for capturing events in Physics Experiment at Brookhaven National Lab. It was done with a hand drill, and I remember the professor telling me that it created 128 Ohm impedance. The object was not to twist to tight or to lose. That was way back in 1981.

[stj]

a failed dc blocking cap in valve circuits can cause transformers to burn up from exess current flow

[desert-rat]

There a couple of YT videos on the different kinds of capacitors , why there used in that circuit , ect.

[Crystaleyes]

Originally Posted by keeney123

This article is good at explain twisted pair and why they are use.

https://audiouniversityonline.com/twisted-pairs/

When I work for UMass I remember one of the professors showing me how to twist a pair of wires for a 100MHz ring counter that was used for capturing events in Physics Experiment at Brookhaven National Lab. It was done with a hand drill, and I remember the professor telling me that it created 128 Ohm impedance. The object was not to twist to tight or to lose. That was way back in 1981.

Great information.

Thank you very much!

[Crystaleyes]

Originally Posted by stj

a failed dc blocking cap in valve circuits can cause transformers to burn up from exess current flow

Tbh I have never even heard of a 'blocking cap' but it is now catalogued in my subconcious archives.. So cheers.

This 'thing' is an old (1960's) Philips receiver/amplifier which is all solid state, so this won't apply right here.

Managed to get both channels working however the one that had failed is distorting.

Amongst other things, the channel had a failed germanium AC128 32v 1A PNP which I've replaced with a couple of different PNP's (to test) but that makes no difference.

Considering that all the electrolytics and a few ceramics have been replaced, then what else in a circuit might distort the signal?

Enclosing the section in question...

Any pointers are appreciated.

[stj]

if you have a stereo device you can find the fault by swapping parts between the 2 channels

[keeney123]

I would make sure the transistor you replace for the germanium transistor is another germanium transistor. The characteristics of a silicon transistor is different and could very well cause distortion. Here is a link to explain that.

https://robertkeeley.com/2013/09/germanium-transistors/

[Crystaleyes]

Originally Posted by stj

if you have a stereo device you can find the fault by swapping parts between the 2 channels

Very good point. I fact, it had dawned on me that I could compare the two channels' voltages, and had just finished drawing up a complete list of all the voltages from the schematic, which I can compare to the actual readings.

Seeing as it is highly possible that the silicon replacement for the germanium isn't helping, then that can easily be switched over to confirm, one way or the other.

[Crystaleyes]

Originally Posted by keeney123

I would make sure the transistor you replace for the germanium transistor is another germanium transistor. The characteristics of a silicon transistor is different and could very well cause distortion.

Just about to confirm that one...

[Crystaleyes]

So...

Using the same AC128 germanium on the bad channel resolved the problem...!

It is not 'quite' as clear as the other channel, but I think once connected up, that only an audiophile would clock the difference.

This receiver/amp goes into one of those cabinet/furniture art deco pieces with the multi-play record deck,which my gran used to have, so really, I doubt that at 31W max that it will even be noticeable.

Famous last words.


Thanks again for the input chaps... Even though I was aware of the audio heads preferring ge in older stuff, I had no idea that germanium or silicon affected the sound so much. Now I do.

We live and learn!


and... I'm gonna twist together both the input and output wires!

[keeney123]

Originally Posted by Crystaleyes

So...

Using the same AC128 germanium on the bad channel resolved the problem...!

It is not 'quite' as clear as the other channel, but I think once connected up, that only an audiophile would clock the difference.

This receiver/amp goes into one of those cabinet/furniture art deco pieces with the multi-play record deck,which my gran used to have, so really, I doubt that at 31W max that it will even be noticeable.

Famous last words.


Thanks again for the input chaps... Even though I was aware of the audio heads preferring ge in older stuff, I had no idea that germanium or silicon affected the sound so much. Now I do.

We live and learn!


and... I'm gonna twist together both the input and output wires!

It is important to keep those germanium transistors cool. Make sure the components around the transistor are with-in specifications. You do not want to overdrive those transistors any anyway. You also might check to see if you can locate a used one that maybe has no damage.

[Crystaleyes]

Originally Posted by keeney123

It is important to keep those germanium transistors cool. Make sure the components around the transistor are with-in specifications. You do not want to overdrive those transistors any anyway. You also might check to see if you can locate a used one that maybe has no damage.

Thanks for all this advice. Most appreciated!


Astonishingly, I found an AC128 in my components vault, down in the dungeon.

Btw, these are the square ones with a hole through (photo), which enables them to fix to the large heatsink.

All the nearby components are original, to spec, or as near as possible (i.e. the 1.6µF is now a 2.2µF and the 125µF is now 150µF). All the transistors are as specified in the schematic.
The only components which I went 'off-piste' with were the 2 x 2200µF in place of the 1000µF main output caps, and a 100µF instead of a 64µF on the balance.


As for the one channel quality. Turned out it is the cable which is bad, for when the connectors were switched the channel quality switched too.

So, now after 30 years the record player and aux input are working, however the radio is still dead. There is a empty space where the decoder board went...

Radio stations only play shit anyway!

[stj]

a cap that reads higher uF than it's marking usually indicates it's internally failing.
the internal electrical leaking fools the cap meter.