Ancient Op Amp - Page 1
Forum section: electronics / general

author: Lee Leduc
author_rank: Regular Contributor
timestamp: May 05, 2015, 06:01:58 pm
content: Hope this is the proper forum for this. If not, I apologize.I found this fossil while scrounging around my lab. It came from some old hardware used on the Apollo space program. It's an Analog Devices Model 170 Op Amp. I'd love to fire it up just for fun but can't locate a datasheet for it. I've tried various search phrases but I've struck out with Google. I contacted Analog Devices and they checked their historical archives but their datasheets only go back to Model 171 (so close) ! Any one have a datasheet or know where I can find one?Thanks

author: c4757p
author_rank: Super Contributor
timestamp: May 05, 2015, 06:15:03 pm
content: Is it potted? I'd love to see inside...

author: Lee Leduc
author_rank: Regular Contributor
timestamp: May 05, 2015, 06:31:50 pm
content: Yes, it's potted. It's a solid block measuring about 2.5cm wide X 3.5cm long X 2cm high.

author: Zero999
author_rank: Super Contributor
timestamp: May 05, 2015, 06:31:59 pm
content: It seems a shame to tear it down, especially when it might be worth something.

author: c4757p
author_rank: Super Contributor
timestamp: May 05, 2015, 06:53:44 pm
content: Yeah, if it's potted don't hack at it.

author: niflheimer
author_rank: Contributor
timestamp: May 06, 2015, 11:28:52 am
content: But DO X-ray it. If you really can't find a place to get some X-rays I'm sure Mike would do it for you if you pay the postage.

author: codeboy2k
author_rank: Super Contributor
timestamp: May 06, 2015, 12:46:04 pm
content: Your dentist might be willing

author: TimFox
author_rank: Super Contributor
timestamp: May 06, 2015, 01:22:27 pm
content: We used Analog Devices potted op amps when I was in grad school in the '70s. Out of curiosity, we did unpot (using dental tools) a low-priced unit. We found a metal-can dual transistor (Analog Devices part), a uA702 op-amp IC (early Fairchild op amp used at +12, -6 V supplies) and some normal transistors at the output. We found that these devices could take more abuse from high voltage discharges that hit the output than any of the normal IC op amps.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 06, 2015, 02:33:29 pm
content: Yes, as @TimFox said, it is almost certainly a small PC board with a matched-dual transistor at the front-end, and a pair of higher-power transistors at the output. And maybe an integrated or discrete op-amp between. These offered convenient "building block" modules for building larger circuits. Even up to modern times, there is still a market for those op-amp modules. While modern integrated circuits can reproduce most of the performance of those modules, there are still applications where the discrete op-amp modules are preferred.For example, large audio mixing consoles starting with API, used similar potted op-amp modules extensively. There are still both assembled modules and kits available for these.http://classicapi.com/catalog/product_info.php?products_id=136

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 06, 2015, 03:28:23 pm
content: Mostly on topic, but it's a pretty good thing to do sitting down and building your own op amp out of transistors i.e. build your own one of those modules. You can build a simple one with a single current source (a resistor will just about do it if voltage is constant), a differential amplifier pair and an output buffer in about 20 minutes flat.If you're googling, ignore the EDN article on it though, as it's complete horse shit.

author: jlmoon
author_rank: Unknown
timestamp: May 06, 2015, 03:49:15 pm
content: Quote from: TimFox on May 06, 2015, 01:22:27 pmI still have some as well.. both Analog Devices and Burr Brown parts. They were some really cool parts back in the day.

author: SeanB
author_rank: Super Contributor
timestamp: May 06, 2015, 06:41:06 pm
content: I depotted an OPAMP LABS amplifier a few years ago to fix it. Steel case, resin encapsulated ( so responded well to a soak in acetone for a week) to get it apart to the point I could replace the cooked output transistors, diodes and resistors.Replaced them with others, and it worked, though there were some track repairs needed, and the original ceramic decoupling capacitors did not survive the solvent. Opamp inside is a LM308, buried under that block of yellowing epoxy. Scary is that it was originally being used as a gain of 2 video amplifier, driving what was essentially a 7R5 load with video. Thus the upgraded transistors with cooling, seeing as the originals were some generic NPN and PNP 100ma devices. They had cooked themselves ( and the 2 diodes) into char, along with the 2R2 resistors.

author: TerraHertz
author_rank: Super Contributor
timestamp: May 07, 2015, 03:12:16 am
content: I have an AD databook from 1978, and the 170 has been dropped from that. It does have a 171, which is a high voltage differential FET amplifier. And the price list in the back says it cost US $92 in single quantity (in 1978.)Pic of index from manual.I've never found data on the AD 118A I have. Though, did not try hard.

author: TimFox
author_rank: Super Contributor
timestamp: May 08, 2015, 01:15:12 pm
content: Your post jogged my memory: that was an 118 that we de-potted.

author: richard.cs
author_rank: Super Contributor
timestamp: May 08, 2015, 08:51:26 pm
content: I have some similar looking op-amps from a box of junk from a place that did test gear repair, I shall have to dig them out. From memory some are potted, some are in metal cans with glass seals similar to an OCXO.