Fastest TO-3 Devices...?

[EchoWars]

Got a dead Kenwood L07M II that uses the uber-fast NEC 2SA1007A and 2SC2337A output transistors. These are 150V, 10A, 100W, 50MHz devices (the C2337A is supposedly 70MHz).

Fastest thing I have around here are some old 2SB600 and 2SD555's (14 and 15MHz, respectively).

Any other options? Someone recently posted that TO-3P's can be inserted into the TO-3 socket, but that seems a cheezy solution...

[ilimzn]

I don't think there are any that are not long obsolete. You get the same problem tryig to fix Sansui AU-X1 - the original RETs are no more, very rare, and very expensive. Compared to the hoops you have to jump through to get some, putting a TO3P into a TO3 socket is a relatively mainor cosmetic issue
The thing is, TO3P has changed through the years too. Originally it started with a tab that looks exactly like 3/2 of a TO3 footprint, with a bit chopped off next to B and E, but retaining the rounded part around the (now) single mounting hole. Curently, the tabs are rounded rectangles, or rectangles with camfered corners, so if you go this route, check that they fit.
As for types, Sanken has some smaller members of the 2SC3264/2SA1295 that use the TO3p (or similar Japanese equivalent) case.
Toshiba has smaller versions of the 2SC5200/2SA1943 in something sufficiently similar to TO3P, 2SC5198/2SA1941, but they are slightly slower than the current Sanken offerings.

[EchoWars]

Indeed, modern TO-3 offerings are woefully slow. Was a lot of good, fast Japanese transistors available back in the day.

As far as swapping a TO-3P for a TO-3, I don't know what I was thinking...the L-07M II has the power transistors sitting in a recessed area of the heatsink...there isn't anything that is going to fit in there except another TO-3 transistor.

I'm amazed that the subject hasn't gathered any more interest here in the forum than it has...perhaps the TO-3 is rapidly being abandoned (and for good reasons), but there's still a lot of very good equipment out there that needs attention and uses the old standard...

[Apogee]

Both originals are in stock here:

http://www.mark5.co.uk/search.php

You might also check out the following 25 MHZ pair as a possibility because they're readily available. However, since they're not T03 cases so they may not work.

NTE2328 & NTE2329

http://nte01.nteinc.com/nte/NTEMasterxRef.nsf/$$Search?OpenForm

Hope this helps

[EchoWars]

Yeah...I saw that.

£25 each, $150 US for the NPN's only. I don't think so. Or at least the owner of this amp is likely to say that. I'll run it by him and see, but I have no method of confirming that these are genuine NEC originals, and the price is just so...

RE: The NTE. Can't use anything except TO-3, and NTE blows anyway. But I appreciate the effort.

[lineup]

Originally posted by EchoWars

I'm amazed that the subject hasn't gathered any more interest here in the forum than it has...
perhaps the TO-3 is rapidly being abandoned (and for good reasons),

Nelson Pass has once, long ago, in this forum expressed he likes to use TO3.
They are robust and can take a lot of heat. (200 degrees, compared to 150/175 for others).

Some P, plastic cases, ( TO-3P ... ) require some care not to screw too hard. (momentum).
TO3 metal housing and the location of holes makes it difficult to damage transistor
by using too much force.

Among the general DIY-ers, TO3 have the drawback of special ways to attach to heatsink.
Either use special TO3 heatsinks or use some bar for indirect attachment to sink.
You also may have to use some insulation covering to avoid shortcuts.
I think these practical issues has made TO247 and plastic devices more popular among the average DIY-er.

Still TO3 has got very good temperature qualities as well as mechanical robustness.
So I, personally, would in each higher power amplifier consider using them.

=============================================


About fast TO3.
It is true there is not many really fast TO3.
At least not around that I know of.
But there are few that have fT higher than 2-3 MHz.

OnSemi ( Motorola)
MJ15022-MJ15025 ~4MHz
2N5883-2N5886, 25A, 200W, ~4MHz
... and some others.
The common use of these transistors, with Emitter Followers output
makes 4 MHz an acceptable speed, in relation to the job they do.
These transistors are not mainly intended for >1.0 gains.
They are for delivering High Currents and Powers, at a resonably high audio frequency.

It would be nice if we had a universal transistor.
One that 'had it all':
- with the gain (hFE 600) + bandwidth (fT350MHz) of small TO92
- with the power of TO3 (>250 Watt)
.... but sorry, I guess we have to to wait some 10 years more for this.
=========================================

You can search for yourself, at www.onsemi.com (motorola)
They have a very nice parametric search.
In the filter function they call TO-3 = TO-204


Good luck!
lineup
.................................................. ...........................................
some links:
Solid State >Easy to find, inexpensive audio power transistors
onsemi.com
OnSemi.com > Product Catalog > Bipolar Transistors

[Piercarlo]

Originally posted by EchoWars
Got a dead Kenwood L07M II that uses the uber-fast NEC 2SA1007A and 2SC2337A output transistors. These are 150V, 10A, 100W, 50MHz devices (the C2337A is supposedly 70MHz).

Fastest thing I have around here are some old 2SB600 and 2SD555's (14 and 15MHz, respectively).

Any other options? Someone recently posted that TO-3P's can be inserted into the TO-3 socket, but that seems a cheezy solution...

The pair 2SC3281 and 2SA1302 was offered in TO3 case by Motorola and pheraps someone other. However don't care for speed (useless because "speed" is not related with Ft; the switiching times of these devices are roughly the same of old "slow" bipolars); the real plus of this kind of transistors is good linearity Hfe at high collector current

Hi
Piercarlo

[x-pro]

Originally posted by lineup

It would be nice if we had a universal transistor.
One that 'had it all':
- with the gain (hFE 600) + bandwidth (fT350MHz) of small TO92
- with the power of TO3 (>250 Watt)
.... but sorry, I guess we have to to wait some 10 years more for this.

What about 500-1000 small signal transistors in parallel?

.

[lineup]

Originally posted by x-pro

What about 500-1000 small signal transistors in parallel?
.

Well, don't laugh!
It all has been tried.
At least many Op-Amps in parallel to make a Power Amplifier.
( see pictures in another topic )

And at least many TO126 ( like BD139 ) in parallel
... covering the whole of a big heatsink.

About TO92 .. I do not know.
But would surprise me a lot, if not some FANATIC has already done this


lineup

*** The highest max power for some TO92 is 1 Watt.
At least 0.6-0.7 Watt we could squeeze out of one, maybe.
Then you do the math ... how many