In Theory oxygenatom can get thru plastic housing of IC wihtin 10 years... But in practice, does it count?

If used, you cant know its history, so new is better imo, but when it comes to obsolote parts, there is also counterfits. I would consider modern subsitute if it is carefully picked up and adjusted to circuitity.

The TBA 931 is not a good op-amp for audio. A lot of the earlier Revox B77's use the same IC; a service bulletin states how to replace the 931 with a more modern TL072 or similar with the same pinout. You don't have to spend money on an obsolete IC and the sound quality is better with modern IC's 😕

ftp://ftp.studer.ch/Public/Products/Revox/Revox_A700/TBA931_Replacement_Rev2.pdf

Integrated circuits will usually not degrade by just sitting around, but be aware that some models of the 931 won't be happy if your circuit exceeds +-13 volts.

Well, I for one like replacing things with the same references whenever possible. I don't care much for so-called sound improvements. You have to keep the sound balance wanted by designers and often painstakingly obtained with what they had at the time, be it first gen. ICs or germanium transistors. You don't want to ruin that.

That said, ICs usually don't degrade unless put under a lot of strain. Sometimes a bad capacitor will cause that, I've had that quite a few times. NOS silicon components, unless they are Chinese counterfeits, are usually fine. 

But sometimes, ICs or transistors are impossible to obtain and you have to find another way.

I recently battled very hard to find transistors for a 1982 amplifier, and I finally won. I managed to find NOS components, albeit at a price!

Hi Guys,

Thanks for the help.

Søren, I don’t know if it makes a difference, but the part number is a TBA 231, not a TBA 931.

I am waiting for my tech to show up for work…. he usually arrives at around noon (Nice work if you can get it….) and ask him what he wants to do.

I have the 2 original IC’s on the original board, if I want them for US$50 plus shipping. The seller is well known to me, BUT there is no guarantee that one or either IC is good.

I found 2 NOS IC’s on eBay, but either could be bad from age alone and I am aware there are counterfeits.

My tech told me before I started trying to locate this part that he found several “replacements” for the TBA 231, but some have less than the 14 pins and one did not utilize all the pins. Neither sounds like a proper replacement to me….. but I am NO expert.

Thanks for the advice….. even with the disagreements. (Hey, that’s how we all learn!)

Jeff

Ah, I was a bit too quick to answer there!

The TBA 231 has some equivalent types still being made today; Fairchild uA739 and Motorola MC1303. 

They have the same specifications and are just another manufacturer's version of the same op-amp, use it as a drop-in replacement. The uA739 can be found pretty easily online.

Hi Søren,

Thank you so very, very much!

Is one better than the other?

I see that the Fairchild in manufactured today in Korea. I assume this is much better than Chinese.

The Motorolas I find are 1970 vintage NOS.

Jeff

I'd go for the NOS. You don't want Korea in your Tandberg, or China for that matter.