Where have all the video transistors gone? (needed for wideband amplifier)

Good surmise! I recently measured some humdrum MPSA42's, which IIRC are rated at 300 volts max. Well with 1K ohms between base and emitter, to bleed off leakage current, they ran just FINE with 800 volts on the plates, er, collectors. Every one I measured out of a batch of 100 worked fine (AT ROOM TEMPERATURE) at 800 volts, most broke down around 830 to 860 volts. I wouldnt recommend doing this as a regular thing, for mil-spec job, or for a nuke-bomb trigger, but you might be just fine pushing the ratings to say 30% below the measured breakdown voltage.

Also fainter in my memory was my measures of some high-speed transistors to replace those whiz-bang ones Tektronix used as vertical output transistors. The specs were around 25 to 30 volts, but with a small drive resistor, none broke down below 75 volts.

Note that this isnt necessarily a poor practice: for example, A LOT of transistors in Tek scopes are "selected" more humdrum types, being pushed waay beyond their rated limits of voltage, leakage and speed.

For example, the CRT grid blanking driver transistors in the 4xx series of scopes are asked to switch about 120 volts in a very few nsec-- if you look up the ratings for the 2Nxxxx part, the rating is I faintly recall, 65 volts and 15nsec. They must have culled a LOT of these transistors to find a few golden ones, or maybe they found a batch that were way better than spec-sheet specs.

Hello Laurent,

With the probability of most CRT being available in the next few years diminishing I guess the same will happen to video transistors. I used to design around a BF type, forgot which one because it's been long ago. It was in almost all European color TVs but now these are migrating to LCD.

You might want to try FETs in common gate configuration. That's what I did a few times for fast amps that needed to generate a few volts out into a load. Mostly because there was less of a chance of them going obsolete on my client since they were popular in switchers.

These are still in production by Sanyo, and MCM will deliver them with 1 to 2 month leadtime. IMHO, it's not so much the high f_T that makes these transistors valuable, it's the low output capacitance. These two go hand-in-hand, of course, but if you concentrate on the capacitance and load impedance issues, you may find other satisfactory parts.

Wow. Pretty impressive.

Yes, all the part numbers starting with 153 IIRC. If Tek got away with this method, why shouldn't I try...

Right, this may have been a very expensive process, apart from the fact that you can only hope to find enough good parts in the future to keep your production running.

Thanks a lot, Laurent.

Not really. Look up BVCER.

...Jim Thompson

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This might have been something like BF869 or 871. These have of course also disappeared.

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Hmm, even small signal FETs like BSS138 (N channel) and BSS84 (P) seem to have a somewhat large Coss (13pF for the BSS138, 10pF for the BSS84) for this application. I will have to try this out.

Thanks a lot, Laurent.

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Thank you very much for the MCM hint, this is very valuable!

Of course I have been looking on

Thanks a lot, Laurent.