Vintage solid aluminum electrolytic capacitors ... replace or keep?

[Klondike Mike]

I came across a radio parts list that contains "solid aluminum electrolytic capacitors". Historically, what has been the experience from those in the "know" about these solids as compared to non-solids. Should we be replacing these with non-solids or leave be? I want to make sure I do not overlook these items if required in my kits.

Quotes from Wiki:

"Aluminum electrolytic capacitors with non-solid electrolyte are the best known and most widely used electrolytic capacitors. "

"Types with solid manganese dioxide electrolyte have served in the past as a "tantalum replacement"

"Most modern aluminum electrolytic capacitors with non-solid electrolytes nowadays are very reliable components with very low failure rates, with predicted life expectancies of decades under normal conditions."

 

[Handy Andy]

Wow! I can see why you are asking - confusing term. Does it mean SEALED Aluminum with Electrolyte or Aluminum with SOLID Electrolyte - so I defer to the package outline. use what fits the outline - Vishay may have quit making the "Tantalum" part due to "Conflict" issues in Zaire (formerly).

The only time I've seen any references, is in a Military Spec on a reference handbook - quite a while ago.

Whoops, found something - these are a type of aluminum oxide cap that is a lot like Tantalum - but instead of using Aluminum Oxide, they use a Manganese Oxide - which in that handbook is the reference to Tantalum

Article is here....
https://en.wikipedia.org/wiki/SAL_electrolytic_capacitor

Most A-typical Electrolytic caps have a thermal rating of 105C - which denotes more of a "Computer grade" while the Tantalum you look to replace with these Solid Aluminum have a rating of about 200C - on a side note, the Caps that the typical CB radio used back then and maybe even still now, are about 80C to 85C for comparison.

What radio is on that list that would use that?

(Thinking their Power supplies but then RF - could use the higher thermal ratings.)
:+> Andy <+:

 

[Klondike Mike]

What radio is on that list that would use that?
:+> Andy <+:

Realistic TRC449 (21-1562)

 

[nomadradio]

I have never seen that one fail.

Even so, I would probably replace it with a plastic-film cap. I don't see why an electrolytic makes more sense here, maybe the available space? The 'lytic will be smaller.

But I think the reason for choosing that particular solid electrolyte/dielectric has more to do with reducing leakage current. The film cap will win out on that one every time.

A normal aluminum electrolytic with a higher-than-needed voltage rating might work okay. Higher voltage rating also means a higher leakage resistance inside. A 50-Volt or 100-Volt cap would probably replace the original part just fine, as well as a film cap.

A cap with too much leakage current will probably be noisy.

73

 

[Klondike Mike]

Thanks Andy/Nomad for your input.

I have never seen that one fail.
Even so, I would probably replace it with a plastic-film cap.

There are 8 of those in the 449. Therefore, I will not be including replacements for these in any of my Electrolytic kits.

... A 50-Volt or 100-Volt cap would probably replace the original part just fine, as well as a film cap.

I came across this earlier regarding using too high a voltage rating for an electrolytic;

Quote from:
Robert Kollman, Senior Applications Manager, Texas Instruments
Power Tip 50: Avoid these common aluminum electrolytic capacitor pitfalls

"This life-temperature dependence actually impacts how you should derate the voltage on the capacitor. Your first thought might be to increase the capacitor’s voltage rating to minimize the possibility of a dielectric failure. However, doing so can lead to a capacitor with a higher equivalent series resistance (ESR). Because the capacitor typically has a high ripple current stress, this higher resistance leads to extra internal power loss and increased capacitor temperature. The failure rate increases with the increased temperature. In practice, aluminum electrolytic capacitors typically are used at about 80% of their rated voltage."

 

[nomadradio]

The TI guy is dead on the money with regard to power-supply decoupling.

But this capacitor is only blocking DC in an audio path. No ripple current here to speak of. Using the 50-Volt aluminum electrolytics seems to help the leakage issues in a signal circuit.

And a tantalum might be the best compromise, at least in size.

73

 

[357]

https://www.badcaps.net/forum/showthread.php?t=52337

 

[Handy Andy]

I have some final thoughts,

In looking over the schematic, and thinking about the "audio quality" - the SAL is only on the output of the FET "Drain" end - it's a Audio Switch function - not necessarily an amp - just a toggle for the SSB mode conversion output. (TR15 is the conversion output) while TR12 acts to "silence - mute" AM side.

So there's the quandary, you put something in there that isn't a "fidelity" part, it's more of a low-pass - the "Tantalum" in it works to act more like a hi-cut filter. If you put a different part in there the tone of the SSB output will be different. The frequency response of a Tantalum favors more the bass or low-tone versus an Electrolytic that will pretty much pass everything. As a helper, look for C51 a 222 (0.0022uF) this can be changed to a LARGER value to offset some of the tonal treble response you'd have from the C52 being standard Electrolytic - but at the same time you also have an inherited signal loss from lower tone and volume - so use small increments of like 0.0039 (392) for starters on C51 to help.

The strong hint is how the Audio from PA side - C62 (0.0047 or 472) and R91 4.7K favor more treble to offset the lower filtered response curve the AM ANL and detectors work. Look at the value of C38 too - it's 330pF - the output filter from the detector side (1N60's are used here) so they have their own response curve and not much in ANL filtering 0.1uF versus the typical 1uF used these days. So they already know they have to boost the treble on the AM side of things to offset this section otherwise it would sound "muddy" .


This is a give and take scenario - some like the warm bassy sound while others need more treble to help with discernment and clarity of the detected signal embedded in all that noise.


I had done these "tweaks" on the outputs of Cobra 148 and Grants - and Robalo even caught R85 (560K) part of the tonal curve for the offset volume and tone issues between AM and SSB detectors in the conversion process for TR19. It's in there so everything sounds "somewhat" equal in the different modes.

My 2 cents!
:+> Andy <+: