Tantalum Capacitor ESR

[Gold]

I have some old cards with tantalum capacitors. These cards are part of an analog computer that stores voltage levels per clock cycle. I want to keep these as tantalum. I’m fine replacing coupling and decoupling caps wit Al electrolytic’s.

I’ve measured a set on one card. The capacitance values are within spec. The ESR varies from about 1ohm to 10 ohm. Cap value is 5uf/20v. Measured at 1KHz with a DE-5000 LCR meter.

My question is could/ would the ESR value over time change like an Al Electro cap or might these values have been there since new?

 

[Matador]

I know that tantalum, of the common dielectric types, is most sensitive to ESR as a function of total time under elevated temperatures. I can't imagine that your cards have been cooking at 90C for decades however.

I would guess that if the internal temp only strays a bit from nominal temperature that those values aren't much different from when they were new. Tantalum was the low ESR formulation of the time, however has been greatly surpassed by more modern caps.

 

[emrr]

10 ohm does seem high for a 5uF

 

[JohnRoberts]

I have some old cards with tantalum capacitors. These cards are part of an analog computer that stores voltage levels per clock cycle. I want to keep these as tantalum. I’m fine replacing coupling and decoupling caps wit Al electrolytic’s.

I’ve measured a set on one card. The capacitance values are within spec. The ESR varies from about 1ohm to 10 ohm. Cap value is 5uf/20v. Measured at 1KHz with a DE-5000 LCR meter.

My question is could/ would the ESR value over time change like an Al Electro cap or might these values have been there since new?

Tantalum caps were popular back in the day for low leakage so they would be used in sample and hold circuits. Tantalums are also notorious for high dielectric absorption FWIW.

Study the data sheets, modern low leakage Aluminum electrolytic caps might work. I suspect leakage is the important spec.

JR

 

[Gold]

I have had these types of cards working with Al caps before. I think performance is better with tants. Not scientifically tested but the system seems slightly snappier with tants. I will replace like with like for any that need replacing.