[SeanB]

Geezer, you have never used bipolar RF power transistors, they are very static sensitive, not to mention load sensitive, heat sensitive and also have that lovely pink ceramic casing that carries the tag Beryllium Oxide - Caution Toxic. Only good thing was that when installed they really work well.

Valves are so hard to damage because they have a lot of surface on the anodes, and they will happily run till bright cherry red on overload, whilst the bipolar dissipates all it's heat in a tiny bit of silicon around 5 by 5mm, that has about the same heat density as the surface of the sun in the worst case.

[Geezer]

Geezer, you have never used bipolar RF power transistors, they are very static sensitive, not to mention load sensitive, heat sensitive and also have that lovely pink ceramic casing that carries the tag Beryllium Oxide - Caution Toxic. Only good thing was that when installed they really work well.

No. I was thinking of something more like a 2N3055 which, I suspect, has about the same RF response as a slug []

Yes, power density has a lot to do with it, but don't forget that "tubes" are intrinsically current limiting and they are dealing with relatively small currents whereas power transistors are dealing with relatively high currents and the only thing (within the transistor itself) that limits the current is the current gain.

[SeanB]

Geezer, I worked on equipment that was poorly designed, and had a switching transistor that was poorly heatsinked, and badly driven. Peak current was 40A and average was 10A, well beyond your common 2N3055. I used to select the transistors based on BE saturation voltage, as a few mV here made a difference ( along with selecting a 2N2219A driver that had a high gain and would saturate with the limited drive) between surviving a while or going short circuit in worst case or merely unsoldering itself at best. Eventually I got a good batch of BUX40 that would survive, the batch was at the top end of spec for Hfe and most did survive.

A 2N3055, depending on who made it, often has a gain roll off at under 10kHz, not what you would like in an amplifier. I did use some as active loads, by soldering leads onto then and dropping them into a ceramic cup ( old tea cup) filled with cold water. Driven with a 555 timer and used to test power supplies for load stability, they generally worked well until all the water had boiled off, then glowed white hot and burnt out.

[Geezer]

Ah yes! The 3055 would not be the ideal choice for an output stage.

[tommya300 (OP)]

Ah yes! The 3055 would not be the ideal choice for an output stage.

Can economics dictate and dominate the use of the 2n3055, when the application is just for a PA system? The vocal speaking bandwidth needed is just to accomadate 1KHz +/- 10KHz. Or for real cheap sounding Ghetto Blasters.

[SeanB]

Sadly you can get cheaper and nastier than the 2N3055, all you need is to look at those that come in a TO220 package, where the cost of the package is greater than the cost of the die inside. Especially if you are buying an "off spec" device as well.


I do remember having some that were sold as off spec, many were so bad they could not be operated at 20% of the ratings, and were all uniformly right at the bottom of the gain range for the type.

I still have a few dozen NOS germanium transistors, some point contact but most are alloyed.

[Bored chemist]

Geezer, I worked on equipment that was poorly designed, and had a switching transistor that was poorly heatsinked, and badly driven. Peak current was 40A and average was 10A, well beyond your common 2N3055. I used to select the transistors based on BE saturation voltage, as a few mV here made a difference ( along with selecting a 2N2219A driver that had a high gain and would saturate with the limited drive) between surviving a while or going short circuit in worst case or merely unsoldering itself at best. Eventually I got a good batch of BUX40 that would survive, the batch was at the top end of spec for Hfe and most did survive.

A 2N3055, depending on who made it, often has a gain roll off at under 10kHz, not what you would like in an amplifier. I did use some as active loads, by soldering leads onto then and dropping them into a ceramic cup ( old tea cup) filled with cold water. Driven with a 555 timer and used to test power supplies for load stability, they generally worked well until all the water had boiled off, then glowed white hot and burnt out.

You had something the size of a 2n3055 glow white hot? What were you powering it with?