Germanium transistor, connections reversed?

[lesmw0sec]

Originally Posted by JonSnell

When I was a test Engineer at Weyrad Electronics back in the late 60s, here in Weymouth, we started using transistors instead of valves. I recall the main one was an XB113. It was a pnp type Germanium, but if put in a multivibrator circuit upside down, it still worked and didn't seem to mind. We found the gain to be about 15 the correct polarity and around 8 (depending on temperature) when reversed the polarity. We are talking an unusual to us 10volt supply rail. We were used to 250volts on ECC81s acting as flip flops in the counter and my Model 7 was having trouble reading the collector voltages for some reason.
I still prefer valves.

Weyrad eh - that takes me back to school days when I was trying to afford one of their coils, CT2W2 if I recall correctly!

[agardiner]

When I started this thread, I thought someone would come back and say I was mad and had clearly tested the transistors incorrectly.

It has been very interesting reading everyone's experiences.

[Craig Sawyers]

Germanium technlogy is alive and well in active devices. Defined as an alloy of Silicon and Germanium with Carbon the resulting transistors have an fT of 40 - 50GHz, although some of them (eg BFP840FESD) have an fT of an eye-popping 85GHz. They have a tiny Vceo of a few volts however. Astonishingly these phenomenal devices are about 30p each.

SiGe part of the core technology in Croy and Tektronix oscilloscopes, which currently go from DC into the high tens of GHz. I expect that they have to be handled with kid gloves to prevent them from being damaged by excess voltage though!

Craig

[G0HZU_JMR]

Yes, Germanium is still in widespread use today. A few years ago I designed a quick and dirty 50mW LO amplifier for use across 5.8-6.0GHz using a similar SiGe (Silicon Germanium) part. I think it was the BFP650F and it has an Ft of 42GHz.

https://www.infineon.com/dgdl/Infine...690f03d9ba3932

The amplifier only runs at about 3V but the 1dB compression point at 5.9GHz was over +17dBm (50mW) when measured on a lab power meter.

There's a few old pictures of the 6GHz prototype amplifier below. It was designed using Eagleware Genesys and Sonnet EM software and with these tools the whole PCB layout is part of the initial simulation. When the first prototype was milled it showed very similar performance to the simulation.

[Craig Sawyers]

Now that is impressive!

Is that a ceramic board?

Craig

[G0HZU_JMR]

Thanks! Yes, it does contain ceramic material and the manufacturer describes it as below

Rogers RO4003C materials are proprietary woven glass reinforced hydrocarbon/ceramics with the electrical performance of PTFE/woven glass and the manufacturability of epoxy/ glass.

SiGe parts also make good oscillators because they are supposed to produce low 1/f noise.

I always assumed that it is risky to reverse the connections to Si BJTs because the base-emitter junction will usually have a lower voltage and current rating. Are there some Ge parts that don't have this limitation?

[Graham G3ZVT]

No one has mentioned the UJT, which, if I remember correctly, is intrinsically symmetrical.