- This topic has 5 replies, 3 voices, and was last updated 2 weeks, 5 days ago by Guenni75.
February 12, 2020 at 14:35 #8275LectronFanModerator
The more I experiment with Lectron, the more I spot differences between the different transistors and their use.
They each have their advantages
Let’s look at the Legacy Germanium transistors.
Their advantage is the lower Base Emitter voltage (about 0,3V), ideal for quick switching circuits. They also have a build in resistor (680K, 330K and 100K), which saves mounting space.
But this is also a disadvantage ! Due to the resistors, some circuits simply wont work or need adaptation.
Also, Germanium transistors tend to drift. This means that their amplification factor Hfe is dependant of the ambient temperature. The same transistors differ also. You can try this by building circuit 51a and 51b in the legacy manual and watch the differences in meter reading, even if they have the same resistor value build in !
So, as for the Silicon transistors there’s much more stability.
Since they don’t have the resistor build in, its much easier to adapt their Hfe to the circuit. They don’t drift by temperature which makes the circuit perform better. They need more space on the board though.
Since they don’t leak current (Germanium transistors do), they can be better used for DC coupled stages.
In our Lectron environment, the Ubungs System 1102 and OpAmp labor are 2 examples of a fine marriage between Germanium and Silicon transistors.
And this is what I tend to strive for too ! Many future constructions will show off the advantages of both types.
What are your opinions ?
February 13, 2020 at 15:32 #8278Guenni75Moderator
I have been working with Germanium transistor since about 1960 – as one of my several hobbies. The history with their different techniques was very diverse since 1948: point contact / grown junction / alloy junction / diffusion alloy / drift / surface barrier / mesa / etc., even npn symmetric*.
Every production process had a special goal, so every “type class” had advantages – except temperature, as Frank mentioned. I love the “old” outlines, no plastic, no uniform look. So I am collecting even the very first pocket radios since 1954 with the TO-22 outline from Texas Instruments, Hitachi and Sony. Furthermore the glass versions like OC44 … OC75 or OC602 … OC614. And these transistors are still working very good since that time without problems.
Germanium npn transistors in glass case were the OC139…OC141, described as symmetric* and could be replaced in some applications by two diodes (…?). Philips designed some pocket radios with the OC140 and OC74 as complementary push-pull output stage with OC75 as driver and a subminiature hearing aid transistor OC59 as pre-amplifier. Looking into such radios I must always laugh… that’s the diversity I like – heaven knows why. The look into radios since 1970 is most boring to me.
This very special amplifier is since many years the last active Lectron block in my superhets with pnp types:
The 1-transistor-reflex-superhet I introduced a while ago was another good example for the very special usage of (selected) germanium AM BC pnp transistors – only some Japanese types (drift types ?) worked without changing the bias resistor (or other parts of the circuit). European types only very few with some changes, Russian types were very “special”: extreme amplification / sensivity, oscillation etc.
The germanium transistors in the Lectron blocks (AF: AC173, AC151 and RF: AF126) with the built-in bias resistor may be bypassed by using the (universal) transistor blocks with a socket. Then npn or pnp, Ge or Si, RF or AF, low power or medium power types may be used depending of the actual problem / circuit.
In this photo from ~ 1970 Max Guerth used in this experiment a couple of this socket blocks:
Silicon types are always first choice, but in circuits / models / applications before ~ 1970 I like to go “old” – with all pro’s and con’s.
- This reply was modified 3 months, 3 weeks ago by Guenni75.
- This reply was modified 3 months, 2 weeks ago by Guenni75.
May 11, 2020 at 23:34 #8652bodgerParticipant
Speaking of germanium transistors, I found an old OCP-71 germanium phototransistor and took a close-up picture of it, thought you might be interested.
May 14, 2020 at 15:12 #8663Guenni75Moderator
What a wonderful and detailed photo of the OCP71 – thank you! It’s a Philips OC71 without black painting. It shows the internal construction of the years 1955 … 1960 in Europe.
May 14, 2020 at 19:40 #8666bodgerParticipant
Yes, you may have my permission to use that photograph on radiomuseum. I tried to get a membership there a couple of times over the years, but was unable to figure out the process.
May 15, 2020 at 15:02 #8668Guenni75Moderator
Membership of RMorg:
I had to try how to find the right way… and here is it: on the main page go to the left column to line HELP and click Contact Forum. The new page shows under 1. to get the membership – then follow the “clicks” / language choice and Sign In (and a one time payment / donation of a few dollars for all the hard- and software costs of the foundation – and thousands of members and dozens of admins for their worldwide work).
Enjoy – and best regards,
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