Which solid state parts to stock

[bnwitt]

Now that I have left the tube arena and ventured off into solid state repairs I am finding two facts to be true:
1. I need to study my tushey off
2. There is a virtual plethora of SS parts in typical amplifiers.

My current part stores allows me to make just about any repair needed to most vacuum tube amplifiers on a same day basis as I have 7 nine drawer rolling partrs bins along with mulitble shelving units of amp parts. Reverb pans? Got em. Vox, Marshall or Fender PT or OT? Got em. Switches, pots, sockets, tubes resistors, etc etc? Got em. There are very few items I don't have in stock for tube amp work.

For solid state work, the situation is totally different. In the few months I've been doing this work, one thing I have learned is that there are so many possible parts in a typical amplifier you can't stock even a small percentage of them. The list of power transistors alone boggles the mind. How many different dual Op Amp chips are there? Gazillions maybe.

So, my question is what generic or common parts can I stock that will help me reduce the in and out time for my customers' equipment. I am sure there must be some common or generic items most SS techs keep in stock for this purpose. So far I have realized that I need to keep several tubes of heatsink paste and that my stock of electrolytic caps (though extensive and fairly inclusive for vacuum tube needs) is worthless for SS needs. I would greatly appreciate any insight the pros in here have on what to stock and where to get these items as cheaply as possible. Paying $4 for a 4560 Op amp is probably not a good thing for my profit margin.

[Don Moose]

I would start by suggesting you get hold of an NTE cross reference and the National, Linear and TI op-amp and power op-amp substitution guides - these may be on line rather than on paper, but they should giver you a pretty fair idea what's common as far as parts-in-general go.

The next suggestion is to start studying schematics for whatever you see a lot of, and wait for Enzo to pop into this thread.

Basics would be J102 JFETs, 4558, TL072 and TL074 op-amps, 1N914/1N4148 and 1N400x diodes, 2N3055-equivalents in TO-3 and TO-220, and whatever power op-amp seems most popular.

There are tons of other parts you will wind up needing, but the strategy there is to find out you need one and order 10 or 25 on the assumption that you will need more later.

You may find that in some cases ordering 100 of something dirt cheap (a diode), once you factor shipping, is cheaper than ordering 10.

Hope this helps!

[bnwitt]

Don,
thanks for the reply. Yes indeed I have learned that ordering a quantity lot of common items is the way to go. 1N4148 diodes, DSY relays, 6531 NPN's etc. I'll check into the cross references you mention. It seems J174 FET's are pretty common. Mac97's too. This is the kind of info I need so thanks.

[Garydean]

I started getting further into SS as well a year ago. I started reading Marshall, Peavey and Fender schematics to see what components were most commonly used. Still to this day I'll get an amp in that has nothing close to what I have in stock. I'll place another order and buy another 50 of that item so my stock keeps growing. It depends what area of the country you're from. I just moved to Florida and I rarely get Marshall or Fender amps. Peavey and Crate are big around here so my inventory had to swing in that direction.

[Enzo]

If a guy was just starting out on tube amps, what list would you make? Certainly not all those transformers, and maybe wait on the reverb pan until you need one, but certainly a bunch of half watt resistors - 100k, 220k, 470k 1.5k - and maybe some 470 ohm screen resistors and some 1k 5w as well. and a few cap values. Then it starts... well we can;t leave out this or that, and maybe we should add so and so... Never ends.

How extensive a list should we make here?

Op amps are largely interchangeable. For a while 4558s were everywhere. Now 4560s and 4580s are taking over. TL072? Sure. For amp work, pretty much pick one and stock it. 4560? Fine. 4558? WHy not, they still work as well as ever and they are cheap. Buy them from Mouser for three or four for a dollar. Low noise op amps? Maybe some of those, 5532 comes to mind. I keep some 2068 and other esoteric ones, but mostly you won;t need them.

Those were dual op amps. Peavey and others used to use a lot of TL074 quad op amps. I'd keep a few of those on hand.

Guys can talk about how some BurrBrown IC is "better" or something, but for general amp repair, those things in DIP cover you. I also stock a few in SOIC for surface mount boards - I think I have TL074s that way and at least some 4580s.

I think if you search here, we have discussed transistor selection and other aspects of parts selection and stocking in the past. We can go into small signal transistors, but search first. I would recommend both US and Asian types since their pinout differs. The 2SC1815 and 2SA1015 are a great Asian pair. There are so many US type to chose from.

I get most parts from MOuser, but when shopping for a shelf stocking order, I get out the Allied and Digikey books too. Digikey often comes through on powr transistors when I least expect it. And MCM is a handy catalog to have, especially for contemporary Asian semi numbers.

Both Crate and Fender used a lot of TIP142/147 darlingtons in a TO218, plus they are drop ins for those BDV65 or whatever they were in older Marshall Valvestate amps. Those would be mid power SS amps - 50-150 watts.

Stocking other power semis is sorta a judgement call. GOnna see a lot of older PV SS amps? Then some MJ15024, MJ15025, MJ15003 would be handy. I look upon the first two as almost universal replacement parts for TO3s. Crate used them a lot too. Like the old PV CS800 or something.

Today, MArshall and others are using a lot of TDA7293V power amp ICs. Mouser there. Less common, but still not rare are the LM3886. I tend to but my Motorola (now ON Semiconductor) stuff from ALLied. On the National, I'd check all three big vendors.

Smaller amps still use a lot of 5-leg TO220 power amp ICs, like the TDA 2030,2040, or 2050. You decide how much of that traffic you'll see. I don't stock the 2030s any more, just the 2040s. The 2050s cost more so I stock a few of them too. But I don;t use them where the lower power versions are for $$$ reasons.

REsistors? I am sure you have that covered. SOme of the really small ones might not be happy when you stick a large 1/2 watt behemoth in there, but stand it on end and it will fit. Usually. But I think you will find a lot more low value resistors in SS stuff thanin tubes. 22 ohm, 47 ohm, 10, 4.7, etc. Some of those are in 1 or 2 watt form as well.

Power amps usually have ballast resistors. Most common are 5 watt rectangular cement ones. You will see 0.22, 0.33, and 0.47 most of the time, others more rare. I think .33 most often. There are also amps using 10 watters

My personal appraoch is to build my parts up. I buy something like 1N4148 by the 100, same with 1N4007. I often find resistors are like a penny when you buy a 100 pack, or 1.2 cents... whatever. WHy buy five of them at 20 cents when you can get 100 for the same? When I need some part I don;t have, and it seems like something to keep onhand, then I buy extra. If order a power amp IC, unless I never expect to see another such unit, I buy at least a second chip. MAybe it is a six amp diode rectifier. I buy 10. SOmeday it will go in something. I never use replacement parts like NTE, I have plenty of subs in my stock.

Caps? Your 22u/500v cap won;t come up very often. We see lots of preamps at +/-15v rails, so we see caps - usually radial - like 470u, 1000u, 2200u, in 25-35-50v. You can always use higher voltage, but in dense circuits, that 50v cap might not fit where the 16v cap used to be. I don;t worry too much about larger caps. 4700u/63v are common PV parts and I stock them, but I'd go case by case.

Smaller caps are in the signal path and a small selection is good. A 50v 4.7u cap is not large at all, even compared to the 10v version, so I stock them. A few of 1,2,4.7,10. Not that we use them a lot, but it is tought to come up with one of those when yuo need it using anything else. And when you are overhauling an older transistor preamp, you might find a dozen 2uf/35v caps all dried out trying to couple stages.

[bnwitt]

Enzo,
as alway thanks for the feedback. I really do appreciate it. I will take your and GaryDean's list and do some shopping. You're right, I wouldn't recommend trannies or reverb pans for a stock item in a service shop. I also build clone and custom tube amps so I keep them for that purpose. One thing I do keep that seems to get depleted regularly is vintage style Fender/Marshall footswitches. Seems that for every old Fender or Marshall amp I get in, the owner has lost the footswitch. I think they're like socks in the dryer.

I appreciate everyone's 2 cents here.
Barry

[Enzo]

Yeah, point was it is hard to stop tossing things on the list. You wouldn;t toss those on it, but where do we draw the line?

A lot of parts I have are OEM specific. Transistors have a way of becoming useful anywhere. BUt there is a chip Samson/HArtke uses for speaker relay control - TA 3717 or something I forget - I don't see it elsewhere. But i am prepared for them. Back when i serviced a lot of QSC, I kept IRFZ44 FETs on hand. Those little TO126 drivers PV uses 5331/53332. Never seen one elsewhere as I recall. Certain parts will be common in one brand repairs and nowhere else, so if you see the brand, there you go, but if you don't, then forget the part. Like those 5w resistors Fender uses in their tube amps for the low voltage rails - the ones that unsolder themselves in the Hot Rod DeVille for example.

Seriously, we had a nice discussion of small signal transistors not all that long ago.

[bnwitt]

Seriously, we had a nice discussion of small signal transistors not all that long ago.

Enzo,
I found that thread. Thanks. I'm not sure all of the puns in it were germanium to the discussion.
Barry

[Enzo]

Well we can rectify that situation.