Matching tubes/ valves

[gbono]

Out of curiosity I checked my last batch: they have a fat "S" engraved with what looks like an "I" embedded on it so I guess they are Siliconix-Vishay.
Didnīt buy many because they were out of IRFP250 so I bought IRFP240 instead.

Any of them is overkill anyway, which is good.

More like St for STmicroelectronics also obsolete as of 2004.

Also defining (matching) Vgs(ID) - transfer function of MOSFET - with a single point is like trying to define a line with a single point. Agree that modern MOSFET with ion implanted gate is very consistent and needs no matching.

[J M Fahey]

No, not ST which I also use by the truckload.
This very different "S" looks like a transformer hysteresis curve, with an "i" inside and no T visible anywhere.
In fact later I checked and found it:

and yes, it is Siliconix .

As of points defining a curve, these are not random ones but:

a) I have two points: 0V and the one I measure.
So if they were straight lines that would be enough: origin and one point in space.

b) I know, these are not straight lines ..... but both follow the same Law, Iīm not comparing Linear to Logarithmic or any other function

c) anyway I am more concerned about matching at low current because I am worried about crossover distortion, itīs not by chance that I chose 11mA as my test current (could have been anywhere between 10 and 25mA ) and near turn-on is where you find the most dispersion (assuming they are the same type and batch which is a given), and at such nil current ballast resistors drop nothing so do nothing.

At high currents, ballast resistor drop *swamps* any difference, so they end up tracking very well.

I am quite obsessive and check everything, and found that scoping many drains in turn gave me the same size and shape current waveform.

I trust my ballast resistors even more than store bought ones, because I make them myself out of Constantan wire , not standard Nichrome type.

[gbono]

Why not use "logic" level specified part? I believe you would get VGS way below 1V at ID=250uA. BTW between VGS=0: IDSS and VGS=x: ID=11mA I bet this is a linear part of the transfer curve.

Vishay still uses the Siliconix logo probably because more people remember Siliconix brand.

[J M Fahey]

Iīm in Argentina
Can get most any product or device but importers bring the most popular , widely user version of anything, for obvious reasons.

And I sell to faraway provinces and neighbouring Countries, so whenever there is a problem, itīs good for me (an the user) that a local repair guy can source parts locally, which of course will be the plain vanilla ones.

By the way, Ampeg or Fender or Peavey, Crate, Laney, G&K, H&K and all the "big boys" in general design based on easy to find, cheap and abbundant parts; only Gurus , "Boutique" builders and exotic Hi Fi, all small builders, go for the non standard stuff.

Only main manufacturer who consistently tried to get a step ahead was old time Ampeg, who used 7027, 6K11, 7189, etc. while most others were using 12AX7, 6L6, 6V6, etc.

Has worked for me , I always learn about 25 or 30 y.o. amps going strong and steady , when old faithful customers comment that regularly on Facebook or Forums, even in EBay questions, that reinforces the brand and brings new customers in.

Customers who came to buy an amp with Mommy or Daddy when they were 13 y.o. (I am AMAZED at how well some of these kids play) , now are 25 to 40 y.o. , are teaching Music and send me their pupils.
Or nowadays teach Music at some school and talk the School Master into buying the new School PA from me.

Each contributes a few drops, among all they fill the water bucket regularly.

A colleague once chided me: "hey Juan, do you want to build amps with what can be bought at the corner hardware store? " ..... I answered: "I would if that were possible" .

I grew in the middle of the Rural Pampas (my Father was a beloved Country Doctor) and I remember what was massively used because it stood daily use and abuse and could be easily maintained: Ford F100 pickups, the equivalent Chevrolet made one and a local designed one which looked like a Russian pickup would, all 3 powered by Perkins Diesel engines, a couple John Deere tractors but above them a Deutz made one which was preferred because it could be fully maintained with no need to go to town, specially in the middle of harvest, it was famous because it used only 3 screw/bolt sizes, could be disassembled using gas pipe pliers if nothing else was available, users could buy a small metal case with all parts needed to rebuild the engine, and worst case, you could tow the dead tractor under a thick tree branch and use it to pull the old engine (to be rebuilt later) and fit a new one in a couple hours.

My power amp and power supply is a roughly 3" by 6" single board + heat spreader which can be bolted to the aluminum back panel which acts as a heat sink by using just two bolts (spread a little thermal grease first, of course) , and audio in, preamp feed, speaker out and PT secondary are all plug-in so user can easily solve the dreaded "my amp is blowing fuses" or "the amp has a STRONG buzz and the speaker jumps forward/backwards" problems in 15 minutes instead of posting a long thread in MEF

Mounting bolts have always been separated by 2" and you can mount a 2016 module into a 1982 amp with no trouble and in about 15 minutes.

I have customers who have sold their Ampeg SVT Classic or Marshall from JCM900 to Silver Jubilee to Slash model because they left them high and dry on Tour, and had to borrow some of my amps from local opening bands, which were always chugging along.

Lost a lot of sales to brick sized Ampeg PF350 and 500 (although I usually sell them a 4x10" cabinet for it) because they die like flies and nobody can repair them, not even under warranty, so 6 months or 3 years later they come to pick one of my heads.

The AWSC system does not apply here: if Ampeg or anybody sends a replacement board, even if not charging it, under warranty, itīs treated as a "new import", must go through Customs and pay all taxes and duty.

Not surprising, I bet ANZ or South Africa or Eastern Europe (including Russia) work in a similar way.

In fact itīs far easier for me to sell an amp to a working Pro than to a newbie, who is starry eyed about what he sees in MTV his personal Guitar God is using or what he reads on some Guitar Forum.
Ok, so be it .

[Enzo]

Oh you hit a nerve.

As much as I love Peavey, it used to infuriate me when taking apart a CS800 there would be three different type and size screws on the lid. Many companies will use more than one screw size on a lid, for no good reason. Even cosmetically, what difference does it make to have three 4-40 screws across the rear lip and ten 6-32 everywhere else? Or the front face panel comes off a rack unit with six phillips head screws and four allen screws, all 6-32.