Inventory

[Danlampton]

I am building a repair business slowly but surely. Right now I am getting work from one music store and hope to add others soon.

One continuing frustration is my parts inventory. I have been ordering a few extra of any part I have to order but I am still having to order parts quite often. I repaired an amp last week with caps I had in stock and I loved that feeling.

Are there certain parts I should just have on hand? Any suggestions of what a basic inventory should be?

Thanks.

[Techknowman]

I too, am doing the same thing as you.

If you can open Microsoft excel files I will send you what I have in inventory.
I'm attaching a PDF printout of the above mentioned file.
Techknowman Part Stock.pdf
There are quite a few common parts but some parts are hard to get.
You can contact me via personal email if you want.
Several on this forum was a great help to me.

[Enzo]

Welcome to the world of running a repair shop. I have hundreds of drawers, thousands of parts, and yet every week there is new stuff I need. And mine is a small shop. I can't imagine keeping tabs on a thing the size of Frondelli's shop.

If you are working on stuff for stores, then you are not probaly specializing. As contrasted to a guy who only rebuilds tube amps. I just keep doing what you are doing, order extras. Things like resistors are cheap. Half watt or quarter watt cost a penny or two in 100 lot, so if I don;t have a value, I usually just get 100. Tube amps will use certain values a lot - 100k, 1.5k, 220k, 1meg, and 1k 5w, 470 ohm 2w. Other values are common, like 68k, but I don;t wind up using them as often.

SS stuff like mixers? Lots of resistor values. One you might not thing of is a selection of under 10 ohm. Aside from 1 ohm sensing resistors for power tubes, I see 10 ohm isolation resistorws in the 15v rails of mixers, and a variety of things need 2.2 ohm, 3.3 ohm, 4.7 ohm.6.8 ohm. I don;t need them often, but they are harder to fudge than a 22k. I see PV power amps. They always seem to have a 180 ohm resistor between oposing bases on the output. And all the SS power amps will want some 5w 0.1 or 0.22 or 0.33, or 0.47 ohm resistors for the output transistors. I usually buy those in 10 lot, since a blown up Hartke amp could use that many. And whatever one is used, it is not hard for an amp to burn up a handful of them.

But resistors are common. I used to work on keyboards a lot, now I work on almost none. There was a time I stocked a lot of Yamaha DX7 type keys - Korg uses them a boatload too. But now I rarely see those. I have a few odd plastic synth key groups I will probably never use, but at the time it seemed like a reasonable purchase. Point it I can guess wrong sometimes.


Caps? Pretty much there are tube amp caps and SS amp caps. Tubes - I try to keep in stock 10uf and 22uf axial lead caps in 450 and 500v. I could probably just stock the 500v ones, but I use them enough, and the somewhat smaller 450v parts are nicer for small amps that use them. And a pile of 22uf/25v for cathode bypass. A selection of film caps 630v in .1, .047, .022, .01 is nice. Certainly other values will come up, but those are common. Ceramic or micas in smaller values will be useful - 100pf, 250pf, 470pf SOlid state, well you have to decide what you are working on. Common voltages are 35 50 and 63, and I'd want up to at least 2200uf. SS is more likely to use radial leads, but not always. I keep some small ones, like 1uf 4.7if, but surely 10uf 47uf 100uf, 220uf 470uf 1000uf are common

I usually buy my own selection, after all I have been doing this over 50 years, but I have bought component kits before - parts houses sell them. Ceramic cap kit or resistor kit. Look at the selection. SOme are cool, others will load you up on values you never use.

Look at the things you service. What is in them? Jacks. I keep a selection of CLiff type jacks and also some Switchcraft basic open frame. But you'll never cover them all. If you get into keyboards, you may start to see a certain jack as output jack, I stock those. On the other hand I see a odd stacked double jack in some SWR, and I never saw it anywhere else. I passed on extras, at least for now.

Pots? I gave up.

Semis? You're always gonna need 1N4007s, if you stock 1N4007, you have no need for 1N4002, 4003, 4004... I stock some 3A as well. 1N5408 comes to mind, but I also have hundrds of fast recovery 3A left over rom servicing SMPS for another industry. They work just fine in pace of slow ones. And the universal 1N4148, get a bag of those. I stock a selection of bridge rectifiers, in particular the gray metal 35A ones. You may never need them. I'd hate to be without them. Zeners? 15v 1w for sure. But I do a lot of Mackie repairs, so I also stock a number of specific zeners for them. And that is the thing, while there is great universality in parts, there are also things like that, you only see on one brand - and you service that brand or not.

ICs. You're gonne need op amps - little 8 leg DIPs. 4558 is common in older stuff, now 4560 and 4580 have taken their place. TL072 is still very common. 5532 is a common low noise one. And also the quad op amp TL074. They are scads of others, like 2068, but you may not see those. There are the two common power amp ICs LM3886 and TDA7293V. I'd hav at least a couple of each on hand myself. And small amps - practice amps - often use a TDA2030/2040/2050, the littel five leg TO220 amp IC. Worth keeping a few. VOltage regs, 7815 and 7915 being most common, somewhat less common are the 12v versions, and the occasional 7805. Look at what you work on, You might like some LM317, LM338, and some other variable Vregs.

Oh lord, FUSES. I do keep a good selection of fast and slow fuses in both inch and a quarter and 20mm sizes. But they can tie up a surprising amount of money, so if there is a local place to pick them up, you might just keep only a few on hand. But Marshalls like the T500ma and T1A and T4A 20mm ones. Working on PV power amps? Then 8A and 15A are useful.

Switches, on your own there. I do like to keep the tiny tactile switches in stock - the little square ones with the round button. You see them under the plastic button caps on synth control panels, rack gear panels, all over. They are cheap. On the other hand, you could probably dismantle an old CD plater and have a supply of them from it.

I could go on and on. I think just slowly building up over time works. Trying to anticipat ALL your needs can get expensive. I don;t place an order for each thing, I gather a parts order and place it all at once. I keep stomp switches for Fender footswitch asemblies, and toggle switches for their chassis. But how often do you need one?

Transistors is a never ending quest. SOme I always have are MJ15003, MJ15024, MJ15025, and TIP 142/147 in TO218, but jeez there are a ton more and it all depends what you are servicing. The types that are in all the SWRs don;t come up so often elsewhere. The TA7317 IC in Samson and HArtke amps don;t show up much elsewhere.

[Danlampton]

Wow! Thanks a lot guys. This is very helpful. I appreciate both of you taking time to help me out. I'll start throwing in some extras with each order now.

[Techknowman]

Thanks again Enzo!
Some of the parts you talked about I don't have, but I'm going to add them to my grocery list. especially the amp IC's
I have most of the other stuff.
I too carry MJ15003, MJ15024, MJ15025, and TIP 142/147 in TO218 have used quite a few of theses!

Danlampton, the ones that are the hardest to come by sometimes are the 2SA 2SC series parts.
I buy them from several places.
If you look at my list you will see the ones I have bought, so far they are the most common ones, but I always run into others.
Usually these parts are a little more pricey but I still get 5 if I need 1 or 10 if I need 2. Most of the time I can recoup most of the cost of them in the first repair.

[Enzo]

I lump all the 2S transistors under the name "Asian" transistors. The Japanese and Koreans tend to use that system of numbers. The 2N types, TIPs, and the MPS ones I call USA types. And then there are the BC and BD types. I think of them as Euro. These are MY personal distinctions, not industry ones.

Places like Mouser and Digikey are carrying more and more Asian types. Since most consumer electronics are made in the orient, places that cater to consumer goods repair - places like MCM - have a good selection of them. For a lot of them I like B&D Enterprises. They carry Sanken and I have gotten no fakes from them, at least not yet.

I have no trouble sourcing the 2S number

In US small transistors, something like 2N3904/3906 are a common and useful part to have. I like also 2N4401/4403 for general use. But there are plenty other real nice ones. A few higher voltage ones like MPSA43/93 or 42/92 are good to have. There are good general use 2S small transistors. I like 2SA733 and 2SC1815 for example. You will find most US types have a similar Asian type available. You could replace one with the other in many cases, but the legs are in different order. If you pay attention, that is OK, just turn the transistor sideways and stick the legs in the appropriate hole. But instead of stocking just US or just Asian, I stock both and don;t have to deal with the difference.

The leg difference apparently is only on the small TO92 sizes. Once you get to TO220, all have the same leg arrangement. There is a TO220 pair - 2SA1306 and 2SC3298 - that I started stocking for I think QSC amps, but they started showing up in a bunch of different things, and they are great drop ins for other types in similar applications, usually drivers. ANd MJE15032 and its brothers are great parts.

When you are shopping, look at the volume discounts. Some places as few as 5 of something drops the price, or maybe 10. If the price break is 3 cents, who cares. but sometimes the difference can be a substantial percentage. If a 15 cent resistor drops to 1.4 cents, then your $1.40 can buy you either 10 or 11 resistors or 100 of them.

And get a catalog from Jameco. it is a smaller house than Mouser or Allied or Digikey, but it is aimed more at the hobbyist or enthusiast than to the industrial crowd. They have a lot of sale prices, look for the color boxes on the price list. Might be certain scattered transistor types where the price for one is dropped to the end colum - the 100 lot price. Or some are just blowing out. When I saw MPSA06 for 4 cents, I bagged 100 of them. A great transistor, especially for driving relays or something - 80v and 500ma in a TO92. The MPSA56 is the PNP version.


EAch factory has its own design team, but they don;t like or need to reinvent the wheel with each project, so when you service Peavey, expect to see the same parts used in most of their models. If the mute JFET in a 5150 is a J174, then likely it will also be a J174 in their JSX or Rockmaster. Fender? No one else much uses those crappy plastic jacks with the 9 legs and the clear top, but they do use them a lot. SO if I service a lot of Fender, i stock them. And Fender uses those 5w 15v zeners a lot too, the ones that cook the 470 ohm resistors in the Hot Rod amps. 1N5253? Close? I forget, look them up. Crate uses them too.

Point is, look at what you service with an eye towards common parts. Marshall uses the 5201 IC for switching, much as PV and others used the now unavailable TL604. But others will use relays for the same purpose. I don't see 5201 anywhere else, so if there is MArshall shop across the street doing all the Marshall repairs around, then I wouldn;t buy a bunch of 5201s.

The other side it this is - don;t go nuts. You will ALWAYS be having to order things. You could spend $10,000 and duplicate my parts selection maybe, and STILL need to order a part tomorrow. And some things liks transformers and speakers, I could tie up thousands of dollars trying to stock, and wind up not having the one I need, and never selling the ones I stocked. I always think about ordering extra of something I don;t have , but always with some thought. Will I likely ever need these again? On the other hand I do almost always order a spare, just in case I screw one up installing it. Never forget that human factor.


And be resourceful. I like to strip down old VCRs and cassette decks, just for fun. It's cathartic. I wind up with a nice pile of metric screws and a power cord. But I toss the boards in a heap. Not long ago, I needed a small - one of those half the size of TO92 and sorta wedge shaped - transistor to fit in a hole in a heat sink. I had nothing, and didn't want to order. FLASH of brilliance!!! Out to the warehouse, a cassette deck board was full of just exactly what I needed. Problem solved.

[Techknowman]

My garage is full of "Flash of brilliance" supply stock. LOL
I have drawers and bins of stuff like that.

[Enzo]

Oh man.

I have been soldering for over 55 years now, and have been in professional electronics for decades. I have been doing mostly pro audio since about 1986. But I have also been in the coin-operated amusements field since 1974. SO while I have a lot of amp parts, I also have a whole pile of old jukebox parts in my warehouse, and old pinball and arcade video games. People whine at me for keeping "that old junk," but I tell ya, when you are looking for a trip solenoid for a Seeburg mech, I got them.


You know, weird crap is weird crap, but when one of those rubber chassis shock mounts for an Ampeg crumbles into goo, what you gonna replace it with? Well, I have a few in my drawer, and I am hanging onto them.


You know, we could take just about any sort of part, and fill a page posting about it. Resistors, relays, crimp connectors, cable clamps, etc. Aside from the pretty universal and basic stuff we already mentioned, I think it is more about being resourceful and having an idea where to get things, more than just having everything under the sun onhand. For what I do, I have a pretty good selection to work from, I can usually come up with something. But having a list of resources or a file full of them, is a valuable tool.

Mouser, Allied, Digikey, Newark are my go-to general electronic parts houses. But Jameco has its place, and certainly more specialized places like MCM and B&D are important to me.

Parts Express is a good catalog to have. They concentrate on speakers and speaker stuff. I may find the actual speakers cheaper elsewhere, but PE has a large selection of things like the plastic cup for jacks on the back of a PA speaker, or handles of all types, or metal cabinet corners, whole crossovers and crossover parts, L-pads, etc.

And certainly get tied in with CEDist, the wholesale division of tubesandmore.com, New Sensor, and MAgic PArts. They sell more amp-specific parts.

You need some odd screw or bit of hardware, there's a good chance McMaster-Carr has it. And I don;t work on guitars, but a Stewart-MacDonald catalog belongs on your shelf.

And that brings up catalogs. Searching online for parts is fine, IF YOU KNOW WHAT YOU WANT. I'll go to Mouser and search up 100uf 63v radial lead caps in a hearbeat. But if you don't know what you want, how do you search? Kinda hard to enter, "Those relays with the bump on the end" into the search window and get anything useful in return. ANy house you deal with, GET THE PAPER CATALOG. You can't easily browse the online pages. In the paper catalog, you can flip page by page through the relays, and see the picture of just the odd shaped thing you need to replace the bad speaker relay in some power amp.

When you flip through the potentiometers, you spot at the bottom of the page... NUTS. Yes, the damned nuts for the pots. Send me a bag of those. Looking at sliders, you can see the pin layout without having to download a data sheet for each type in the search selection. And you will find yourself saying "so THAT is what they call those things." Or I didn't know you could buy just that. or you discover a product you never knew existed.

[Techknowman]

One thing that you mentioned in a different post and this one is the subbing of parts.
While I won't use ECG or similar cross reference parts, I wonder if its helpful when looking for a sub?
If part A crosses to an ECG123 and part B does as well, is it wise to use Part B in place of A?
Or what have you found is the best way to sub a part?
Normally I just get the same part number so I don't stress about it.
Every time I sub a part I seam to have some problem and I always "think" its the sub, I'll order the real part put it in, still have the problem then find the real issue.
Its just that mental hurdle of using the sub.

[Steve Conner]

If part A crosses to an ECG123 and part B does as well, is it wise to use Part B in place of A?

No.

The best way of subbing transistors is to read and understand the specs. Vceo, beta at the various current levels it'll see in the circuit, Ft, noise figure for preamp circuits, safe operating area for output transistors, and so on. If you pick a substitute with similar values of these specs it will work. The part number is almost irrelevant.

[Enzo]

Most transistor circuits are remarkably flexible. If I meet the voltage and current specs, and the gain is in the ballpark, it will probably work fine. Face it, most transistors we replace are in power amps, and SS power amp circuits are so massively fed back on themselves, they spend most of their energy correcting themselves. So putting MJ15024 in where MJ15003 used to be doesn;t bother me. I don;t want to mix them, but that is a different discussion.

I just hate using NTE/ECG stuff. I don;t think it is necessarily bad quality parts, but it is not the part I am trying to replace. Having just said transistors can be liberally substituted, I also said I don;t mix. SO when there is a row of MJ15003 in an amp, that NTE cross may be their closest equivalent, but it is not the same part. and as such, when in the line with the rest, it cannot be counted upon to share current equally nor track thermally. You can then wind up with a transistor either coming on sooner and hogging current, or it lags behind and might as well not be there. Not to mention the much higher cost.

SO the answer to that is don't mix. If I absolutely HAD to replace an MJ15003 with an NTE, then I'd want to see the entire row of them become the NTE. Whatever that NTE part was inside, at least they'd all be the same.

I prefer to use the actual part, and most times I can get it. I maintain enough selection that most times I can find a real part in my drawers to replace the old real part when I make a sub. My 2N3904 can replace a zillion small transistors just as easily as their NTE123.

If I encounter a part I never saw before, I will look it up in NTE to see what they'd use in its place. SO aha, it is a PNP, and they replace it with a 100v 150ma part. Doesn't mean my original was rated to 100v. My real part could be a 60v 100ma part, and NTE thinks their 100v 150ma part is a good cross. Probably is, but that is why I can't consider the NTE specs as the same as my real parts. What if I cross my 80v 500ma MPSA06 to an NTExxx (I am making up the example), and they cross me to a 100v500ma part. Then I cross some 60v 400ma part and NTE comes up with the same part from their list. That doesn;t mean my 60v part replaces my 80v part, does it?

SO I use the NTE book to give me gross information about transistors.

When NTE crosses a IC, that can be useful too. Even if the specs are funny, if it works as a replacement, then I can count on the legs having the same pinout. SO if I need to know the pinout of an LM3886, I could look up the NTE cross and the legs would do the same jobs. Also, some ICs you just have no idea what they even are, so NTE cross will at least identify it as an FM receiver IF amplifier or whatever.

But I don't do that very often, because if I have a mystery part, I can just google the part number and find entire data sheets for it. In fact sometimes the information I need is right in the google returns, I don;t even habe to click on one. Google MPSA06 to see what I mean about returns. My computer screen is right here in front of me, while my NTE book is across the room ona shelf. I could get it on CDROM, but why bother. What is this mysterious TA7317 on some power amps? Google TA7317, and BAM... data sheets.

ANd I also more often than not just punch up Mouser. Most parts they sell have a data sheet link right on the line with the part. What kind of diode is a 1N4742? I know it is a diode from the 1N part. And from experience I know 1N47xx is a zener. It just took me 30 seconds - I timed it - to log onto Mouser and find it is a 12v 1 watt zener. And while I was there I saw they have them in stock for 4 cents each as bonus information.


I organize my drawers for substitution. I have a drawer unit for TO3s, one for TO220s, TO92s, etc. And each drawer has the basic specs in the front. SO if I need to sub that cathode transistor in a Music Man, I can look for a NPN TO220 of sufficient voltage and spot a MJE1503x as a reasonable sub. Just looking at my drawer bin.

Does my heart good when I decide on some sub and find out later that the amp maker did exactly the same sub himself. Those darlingtons in the MArshall Valvestates were T65 or BDV65, and a TIP142/147 worked fine in their place. Then later I see them coming from the factory with the TIP parts installed.

Oh yes, we know what the RCA tube manual is. There is a transistor equivalent. MCM and some other places sell the Japanese transistor guide. A master list by number, with a line for each part with specs. SO if I need to sub a 2SA1015, I do have to know what the hell its specs are to start with. I do still use google first, but this book is work the $20 or whatever they get for it. MCM used to sell it, but no longer in catalog I see.

I keep data books from Motorola, now ON Semi, and TI and National. I can look up a data sheet in them too. Moto used to publish selector guides - charts of basic specs. You can still find selector guides on their web sites.

[jrfrond]

Welcome to the world of running a repair shop. I have hundreds of drawers, thousands of parts, and yet every week there is new stuff I need. And mine is a small shop. I can't imagine keeping tabs on a thing the size of Frondelli's shop.

LOL!!! I have to tell you that parts is just ONE of my full-time jobs here. And I have to tell you that no matter HOW large your parts stock is, there is ALWAYS something else you will need. Trust me on that. It just doesn't end. Right value, wrong size, wrong package, vice-versa. Yikes!!!

However, it doesn't have to be nearly as complex as what I deal with every day. There are certain things you MUST have in stock. Fortunately, you can buy a lot of component kits, like resistors, caps, etc. Jameco is particularly good for this, but Mouser and Digi-Key also have kits.

To start, I would get two capacitor kits (one electrolytic, the other poly-something or other), 1/4W and 1/2W resistor kits, a diode kit, transistor kit, fuse kit. It will save you a lot of time and aggravation rather than trying to build assortments. For IC's, you need to have a couple each of the following: TL072, TL072, NE5532, NE5534, NJM4558. All of these are available in through-hole and surface-mount. For power transistors, stock only MJ15024 & MJ15025 (or MJ21193/94) in TO-3 cases. Also TIP31 and TIP32 as medium power TO-220 package, also useful for drivers.

That's the very basic stuff at least. Then you can just order extra of whatever you need as you place other parts orders. Keep in mind that if you are doing a lot of guitar amps, you will need an assortment of pots, and perhaps even carbon-comp resistors for vintage restoration work. While you can find a lot of this stuff at Mouser, there are companies like New Sensor, CE Distribution, and Mojo that specialize in guitar amp fare.

Here's a little hint: we all have computers. If you are handy with Filemaker, Access, or even Excel, you can create a database for your parts to find them in your bins. "Hard-Labeled" drawers become impractical unless they are for parts with a wide value range (resistors, caps, fuses). Get yourself some parts drawers with dividers, and only one transistor, diode or whatever part number per compartment. Parts drawer systems work best with a "3D" binning system. For instance, if you have three parts drawer cabinets, label the first "A1", the second "A2", etc. This is your main SECTION. Then label the drawer vertical COLUMNS with letters, lets A through H, and each horizontal ROW with numbers. Most parts drawers have two or three compartments, which will be respectively called 1, 2, and 3 (if it exists). Now, you can assign a location to each part. Your very first drawer location will be "A1-A11" (the last is NOT pronouced "eleven", but rather "one-one"), which means "Section A1, Column A, Row 1, compartment 1. The next compartment in would be "A1-A12", etc. These numbers get stored in your database as a bin location. Sounds complex? Sounds like overkill? Sounds like I am blowing a lot of smoke about how to store inventory? Wait until you have even a few hundred parts in stock, and you are trying to find a particular one. Do yourself a BIG favor and do this from the start. Don't wait, or it will over take you. A little more work on the front end will save you lots of headaches on the back end, when you need to find the parts.

[Danlampton]

This has been quite enlightening. Thanks so much!