124 (also ebay source available) question about the TI voltage regulator

[pottedplant]

Hey folks a while back I found some TI 7812c's on ebay that are very similar to the ones used in 124 and was wondering if anyone here could tell me what the extra markings on them might mean? As far as I know the seller still has some for sale https://www.ebay.com/itm/166864352448

I'm mainly wondering about the P-3 more than anything. From what I can tell 78 means it's a positive regulator (79 would be negative?) and I saw someone else using a very similar one marked just P+ in their 124 on here instead of P-3. I can't remember who it was, but that got me wondering if it was an important marking and not to be ignored before just hooking it up. I know very little about this kind of stuff so any info that you'd like to share with me about voltage regulators would be great. Does one need to use a mica insulator under these? When is it necessary to do so? stuff like that...

[martin manning]

TI 7812C is a 1A +12V regulator, and that is really all that matters. Should work fine.

[pottedplant]

TI 7812C is a 1A +12V regulator, and that is really all that matters. Should work fine.

Hey Martin thanks for the reply glad to hear it will be okay. I think I will get some new ones too just to have some non NOS parts just in case they don't work right for some reason. You're the best! Thank you for all your help

[solderhead]

every letter and numeral on the part means something significant to the manufacturer and to purchasing engineers, but are often lost on us. the suffixes in the part numbers represent packaging information. that information is published on the TI datasheets if you bother to look at them. packaging info is on the last pages. there's also information that gives you the answers about mica insulators, etc.

Here is the 7800 series datasheet:
https://www.ti.com/lit/ds/symlink/lm7800.pdf

Here is the 7900:
https://www.farnell.com/datasheets/1692723.pdf

I would be careful buying parts on ebay. Many of them are counterfeit. You need to be especially suspicious about them if their markings don't match the manufacturer's datasheets. IMO you're best off avoiding ebay for parts. I prefer to buy my parts from official factory distributors who can provide provenance certification for the parts they sell.

[captaincoconut]

The 78xx voltage regulators are some of the most common and avaialble parts in the electronics world. ANY manufacturer will work, so there's really no need to hunt for a NOS voltage regulator - risk is higher that it's defective and it has no effect on sound anyway as it's just used for switching purposes.

Mica isolator is not needed as the casing is connected to the middle pin, which connects to GND anyway.

[pottedplant]

every letter and numeral on the part means something significant to the manufacturer and to purchasing engineers, but are often lost on us. the suffixes in the part numbers represent packaging information. that information is published on the TI datasheets if you bother to look at them. packaging info is on the last pages. there's also information that gives you the answers about mica insulators, etc.

Here is the 7800 series datasheet:
https://www.ti.com/lit/ds/symlink/lm7800.pdf

Here is the 7900:
https://www.farnell.com/datasheets/1692723.pdf

I would be careful buying parts on ebay. Many of them are counterfeit. You need to be especially suspicious about them if their markings don't match the manufacturer's datasheets. IMO you're best off avoiding ebay for parts. I prefer to buy my parts from official factory distributors who can provide provenance certification for the parts they sell.

I'm aware that packaging suffixes exist and have read many many datasheets over the years looking for parts here. They don't mark the parts with this information usually. An example would be the RN65C1003F 100k resistor commonly sought for the plate loads here. Thank you for sharing the datasheet with me and I saw the P+ marking information. I don't see any mention of P-3 or P- of any sort. I also did not notice any mention of the word "mica" or "insulator" by searching for it (which I already did the last time I looked at the datasheet) in that datasheet can you show me where it says this? I appreciate the warnings about buying from ebay but I will continue to do so because that's the most practical way for me to acquire some of these parts. I'm unaware of any seller who has "provenance certification" for old Sprague orange drops and the like but if you can show me who they are I'd definitely buy from them. There are many people who buy parts from ebay to build their ODS's on here, I don't see them being told not to do so... Why me?

The 78xx voltage regulators are some of the most common and avaialble parts in the electronics world. ANY manufacturer will work, so there's really no need to hunt for a NOS voltage regulator - risk is higher that it's defective and it has no effect on sound anyway as it's just used for switching purposes.

Mica isolator is not needed as the casing is connected to the middle pin, which connects to GND anyway.

I know it doesn't impact the sound, it's just a little piece of history that I'd like to have in my amp build (which is very important to me) and isn't actually a big deal unlike the NOS resistors that no one can find or use anymore. I did mention that both NOS and new production parts are on the table for this regulation duty. You can see that if you look at my reply to Martin: "I think I will get some new ones too just to have some non NOS parts just in case they don't work right for some reason." But thank you very much for telling me about the insulator. I was wondering what the need for one is. I guess I will google it.

Thanks for the help guys, I'm definitely getting closer to putting this amp together

[martin manning]

Counterfeiting of electronic parts is a well known problem. In-demand capacitors, transistors, and IC’s are some of the most common fakes. If new equivalent parts are available through distributors like Mouser and DigiKey that is the best option. Heres a nice article about some power transistors: https://squashpractice.com/2024/01/01/c ... on-shills/

[pottedplant]

fair enough, i appreciate the warning and it was a good read

[solderhead]

The datasheet does mention that the case is ground, as is one of the 3 legs. But they don't tell you how to build whatever device you're building. If you don't care about your ground path then you can mount the vreg directly on the metal chassis in any convenient location, or if your application requires a heatsink you can mount it on the heatsink. If you're persnickety about ground paths, then you should use a mica insulator to isolate the body of the part from chassis/heatsink/ground and connect the ground point from the leg of the device to your preferred grounding location. Doing that will minimize the chance of ground loops and noise.

If you're interested in provenance on your parts, any of the major distributors will have letters available that you can request at no charge when placing your order. Here's an example of the different services offered at DigiKey: https://www.digikey.com/en/help-support

Not only can you get provenance information from distributor, they offer letters of conformity from the manufacturers. They even provide parts tracing, where they will print your order number on the reel of cut-tape that you order, so you can cross-reference a particular part in inventory with the order that obtained it.

[pottedplant]

The datasheet does mention that the case is ground, as is one of the 3 legs. But they don't tell you how to build whatever device you're building. If you don't care about your ground path then you can mount the vreg directly on the metal chassis in any convenient location, or if your application requires a heatsink you can mount it on the heatsink. If you're persnickety about ground paths, then you should use a mica insulator to isolate the body of the part from chassis/heatsink/ground and connect the ground point from the leg of the device to your preferred grounding location. Doing that will minimize the chance of ground loops and noise.

Like I said at the beginning of this post, I don't know anything about voltage regulation semiconductors. I can't know what I don't know so that's why I'm asking here. That's what forums are for. To ask questions when someone doesn't know something and discussing the topic, among other reasons.

If you're interested in provenance on your parts, any of the major distributors will have letters available that you can request at no charge when placing your order. Here's an example of the different services offered at DigiKey: https://www.digikey.com/en/help-support

Not only can you get provenance information from distributor, they offer letters of conformity from the manufacturers. They even provide parts tracing, where they will print your order number on the reel of cut-tape that you order, so you can cross-reference a particular part in inventory with the order that obtained it.

That's not what I asked about but thank you for linking me to digikey. I have an account there, I'll make use of it in the near future.

[ijedouglas]

How rude!

Someone took the time to answer your question and they were met with that response.... perhaps you could show a little more tact when responding to a fellow forum member?

[pottedplant]

How rude!

Someone took the time to answer your question and they were met with that response.... perhaps you could show a little more tact when responding to a fellow forum member?

Which part?

[captaincoconut]

Regarding the mica insulator: it just happens to be the case that the casing of a 78xx-series voltage regulator is also the ground for the circuit. There are other voltage regulators out there however, where the case is not ground but the output or input of the regulator. Those are typical cases where you would use a mica insulator - otherwise you'd create a short!

[solderhead]

^ It pays to read the data sheets.

[pottedplant]

Regarding the mica insulator: it just happens to be the case that the casing of a 78xx-series voltage regulator is also the ground for the circuit. There are other voltage regulators out there however, where the case is not ground but the output or input of the regulator. Those are typical cases where you would use a mica insulator - otherwise you'd create a short!

thanks, i knew middle was connected to the case already just wasn't sure why people were talking about insulators in other threads about it on here. one can do a search and see exactly what i'm talking about. Obviously if I already knew all this stuff I wouldn't have to ask or wonder but that's what this is. Just asking about things I don't know about and getting helpful replies from kind people like you. Some folks have a weird disposition that if someone doesn't know something already they're not allowed to not know it but simultaneously be wrong about it and be held accountable for it lol. It's mental illness but what can you do ya know? The internet has a lot of crazies on it. Thank you for clarifying about the spacer. I can glean from the responses you gave that in circumstances where the back of the package is not ground connected it would be unideal to connect it to anything that has connection to ground. You and I both understand that asking questions and knowing your limitations are a sign of intellect. Thank you for not acting the way some other folks are.