Help with transistor replacements

[Randall]

A Randall amp RG1503 amp came in sounding awful. I found the entire chassis was very sensitive to touch, it made it do all kinds of things. I put some torque on one of the big filter caps, and poof!, a little 4.7 ohm resistor went up in smoke. Odd. Upon measuring the output section I found an in circuit short on one side. I started to unsolder the power transistor, and the legs, one after another fell away. I pulled them from the heat sink, and all four have broken legs. They appear to measure fine, but I can't in good conscience try to solder them back like this. I did find an apparent short in one of the driver transistors, a 2SA1837.

Now the problem is, none of them are available any longer as far as I can tell. They are all over ebay of course, but I try to avoid those. What I need is two pairs of 2SA1941/2SC5198 and a pair of 2SA1837/2SC4793. I have read on another audio site that 2SA1942/2SC5200 will work, and Mouser has those. Can someone confirm this? I have never been to great at cross referencing semiconductors.

And what could I use for the driver pair?

[Jon Snell]

https://uk.rs-online.com/web/p/products/5318946/
https://uk.rs-online.com/web/p/products/0184868/

Drivers are available from most suppliers.

[Randall]

RS does not appear to ship to US.

[nosaj]

Or Audiolabs of Georgia https://audiolabga.com/
nosaj

[Jon Snell]

RS was just an example, there are many suppliers world wide and they are not obsolete.

[tedmich]

so Randall is attempting to fix a Randall amp? Ironical! Seriously though you are stuck with the very high priced and questionable Asian aftermarket when trying to find older obsolete transistors! Lots claim to be these on Alibaba...

RS does have an export division which they say serves NAmerica but only a handful of parts come up in this category and none the nice (seemingly exact) matches Jon found on their UK site (?!)

Mouser has the Toshiba 2SA1941 in stock and their 2SC5200 does look like a beefier sub that should work, but YMMV! Good luck!

[tedmich]

https://www.westfloridacomponents.co...iba%C2%AE.html

cheep!

[Enzo]

The transistors are supremely flexible. Unlike a tube amp where a 6L6 sounds different from an EL34, you can run almost anything here. The 5200 set is just a beefier part. I'd stick them in there in a heartbeat.

[g1]

I think if you want to get pairs of the 1942/5200 you might have to go from the toshiba up to the ON semi to find stock. The ON semi are higher spec'd part.

[Randall]

Thanks guys! Got them all originals at the eelectronics place for $18 shipped. Never heard of them before.

[g1]

Thanks guys! Got them all originals at the eelectronics place for $18 shipped. Never heard of them before.

No offence to Nosaj intended, but that place looks kind of sketchy to me. Lots of stuff in 5 or 10 pcs very cheap. There ebay store looks pretty much like any Chinese ebay seller, just that they are shipping from within USA. Sooner or later the chinese knockoff sellers are going to figure out they need to warehouse in the US, maybe that is what is happening here.

I hope I'm wrong and they end up being ok, but if not you are only out 20 bucks. Here is one of their negative feedback ratings about those exact part numbers:
"apparently they do not meet the parameters. I installed them in a new amplifier that worked and only worked for 10 minutes. They were short-circuited.
1pair 2SA1941 & 2SC5198 A1941+C5198 Toshiba Transistor PNP NPN 10A 140V 100w USA (#223947929715)"

[J M Fahey]

Sooner or later the chinese knockoff sellers are going to figure out they need to warehouse in the US, maybe that is what is happening here.

Guess the same and think weīll have that sooner than later.
Or itīs already happening.

Not practical to warehouse in USA *everything* thatīs on AliBaba or similar BUT it might well pay off for *popular* stuff, where you have a guaranteed market.

A choice selection of much wanted power transistors, Sanken/Sanyo power modules, Toshiba stuff, etc. fits the bill nicely.

Or Eelectronics might simply be dropshipping, you order from them but they are just a front, a user interface, but actual products come from a third party, usually direct from China but maybe from a US warehouse too, which supplies 10 or more "Electronics suppliers".
Just curious about what your shipping label shows as return address, or supplier address?

A couple months ago a guy posted about his problem: he bought some electronic gadget from China.

To his surprise, package contained a sampling of erotic underwear in fluo colours, see through slits in strategic places, the works.

He complained, money was fully refunded, and he was asked to return items to a US address (re-shipping TO China costs 10X product price), which he published online.

Just curious (as always) I searched the address and also in Google Maps.

Place was a huge warehouse, typical old decommisioned Factory building split into 10-20 tenants, (showing US de-industrialization) and that particular unit had a generic mean-nothing name, such as "Universal Trading" or similar, which in due course acted as return address for hundreds of small time AliBaba sellers.

Not sure how it works, whether stuff is later re-sold, or simply let to rot and eventually become landfill or, best case, recycled. (wouldnīt hold my breath on that).
Have read the horror stories on Amazon returns, where many (most) are packed in huge warehouses, with no defined future.

That particular returns Company was registered by somebody with a Chinese name, although he easily could be Chinese-American, who knows?

My point gain being that apparently Eelectronics being an American company does not really mean it actually is.

[Mick Bailey]

I've noticed on Ebay that (at least here in the UK) a large number of Chinese companies will be registered within a very tight radius in a particular city over here. Sometimes within a single postcode. You look at the seller's other items and they present a wide range of totally unrelated stuff and the specific item you're looking for may well be the only electronic part that they sell. The item will show as UK stock but the sellers address will be a flat in some Chinese mega-city. It's then a lottery as to whether the item is in the UK or not. Parts are generally a risky bet from such sellers, but I've had pretty good luck with assembled electronic modules - test units, programmers, interfaces etc. Some are indeed UK stock, some are not and there can be a long wait.

[Randall]

For what it's worth, their email confirmation and track 'your order page' look very good. No language issues or other concerns. It looks to be a very pro operation, at least thus far.

[Randall]

Follow up.

I got the replacements, they look good. I replaced the 1/4 watt 4.7 ohm fuse resistor that had roasted when I flexed a filter cap. Crossed my fingers, switched it on, and the clean channel sounded great. Plenty of volume, tone controls worked, reverb worked. Great, this is fixed. Switched the gain channel on, and a spark, a small flame, smoke, buzzz!. I cut my elbow because I recoiled into something. WTF?

Don't really know why the clean channel would work, but the gain channel would instantly smoke part of the power board in such dramatic fashion, but as far as I am concerned, this Chinese POS is toast. Not worth investigating why this happened or trying to fix it further for me. I told the guy, sorry it didn't fix it. Pay me for the parts I have into it, and we both cut our losses. I don't know if the tranisitors I got were the problem or if there was something else still afoul that I missed the first time, but I'm over it.

I'm going to get to the age where I can receive SS check in a couple of years, and I am going to stop even considering this modern solid state Chinese crap. Can't wait.