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Old 22nd May 2007, 02:57 AM   #1
NIC1138 is offline NIC1138  Brazil
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Default Germanium output stage

It seems that the germanium transistors that are the easiest to get around here these days (if not around the world) are the AC188 and AC187.

The info I found on Internet mentions that these devices would be directed for output stages of amplifiers, specifically in an AB push-pull configuration. There is even a suggestion for building 3W amplifiers, what is corroborated by the fact that the transistors has a metal TO packing.

But these transistors have been extensively used for dirstortion units, and pre-amplifiers (input stages...) In the distortion circtuits they are biased at a very low-current coniguration, what is strange considering that they are director for high currents.

So I ask, does anybody has experience on using those germanium transistors as output stages??...
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Old 22nd May 2007, 04:53 AM   #2
Minion is offline Minion  Canada
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as Far as I know Germanium Transistors haven"t been in production for Many Many Many years(at least 20), ever since Silicon Transistor fabrication have been more or less perfected......

Most germaniums you get these Days will be NOS or old surplus stock.....

I recently Parted out an Old Tape deck had a Built in Stereo power amp that used Several TO-3 germaniums in the output stage (and TO-18 for the input) and for only about 10w output power there were several To-3 devices attached to a HUGE heatsink so it seems that Germaniums must be derated a Lot more than Silicon and are extremely sensitive to heat.....

I posted a question here looking for a Project to use the T0-3 Germanium devices with and every body basicly told me not to bother because of there heat sencitivity and the Lack of High output power.......The ones I had were rated at 4A each and there were 4 used in the output stage for a measly 10w output..

I have found some good uses for the T0-18 devices in Distortion pedal and Guitar effects curcuits though, I am actually useing an old germanium in the preamp/Overdrive stage of my Guitar amp and they seem to have a more tubey sound than Silicon Transistors in the same curcuit.....


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Old 22nd May 2007, 05:15 AM   #3
NIC1138 is offline NIC1138  Brazil
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Well, a high-power application would perhaps be as "unnatural" as the low-power processing ones are!... I'm curious about the "natural" 3W circuits.

I've already seen someone mentioning that perhaps germanium transistors could have interesting caracteristics related to the crossover distortion in class-B amps... Does anybody has an analysis, for example, comparing similar class-AB amps, using germanium and silicon BJTs in the output? What sort of enhancement could them bring??...

The reason I'm obscessing is that it makes me mad to use those "can" transistors for puny 10uA!

I was thinking for example, how does a distortion pedal sounds biasing the transistors at high currents, in a real class-A configuration?... Les sinteresting then the traditional Fuzz Face circuit?...

(I'm about to test for myself... they are just there, looking at me right now)
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Old 22nd May 2007, 10:45 AM   #4
lineup is offline lineup  Sweden
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Default Re: Germanium output stage

Quote:
Originally posted by NIC1138

It seems that the germanium transistors that are the easiest to get around here these days (if not around the world) are the AC188 and AC187.

----

So I ask, does anybody has experience on using those germanium transistors as output stages??...
.
AC188 and AC187.
yes, correct

I have a few of those type.
They are still small
but can make power enough to make a good sound level
in normal/high sensitivity small speakers.

Those ones I have are found in:
output stage of old transistor radios.
Sometimes in old car radios, with or without cassette players.


If you can find Transistor radios or Car radios from period 1960-1979 ... maybe
In surplus, garage sales, in old attics and in the junkyard
you may get this old craap very cheap
( maybe pay by the weight, a few Euros per kilogram )


Then is the hard work to do
.. open up cases and use you solder iron
to try to get them off board.
------------

I really do not know what to do with my Germanium Power transistors.
I keep like 5-6 of them in a paper box.
------------

But, as I said, you can scan the eBay and get plenty of those for 'no money'
if you hit nd know the correct age of those oldies radios.

Other persons here,
'vintage radio specialist & collectors'
would know better and could tell you what to look for in 'Sales Ads'.
More specifically.

Germanium based old audio gear --- should be a BARGAIN any time
.. who wants such junk
.... nowadays


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lineup
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Old 22nd May 2007, 11:01 AM   #5
sreten is offline sreten  United Kingdom
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Hi,

Germanium transistors are used when the low Vbe (0.2V) compared
to silicon (0.6V) can be exploited, one area is distortion pedals.
They are used probably because they are easy to get, and as medium
power transistors they are relatively low noise at low impedances.

/sreten.
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Old 22nd May 2007, 03:59 PM   #6
NIC1138 is offline NIC1138  Brazil
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I bought these transistors for research. I want to measure the best way possible the distortion curve and filtering. If I can replicate the distortion with silicon, the fad is buried!

But one of the biggest problems is that it is already difficult to reproduce a germanium circuit using germanium transistors!!!

Some people claim that with germanium they are reproducing the output o an old amplifier, and this is the signal feeded to the new amplifier, that does the power job. But what I started to realize is that the distortion circuits are very different from old (or new) amplifiers... So, this doesn't make sense. They are actually circuits designed for distortion. This "reproduction of old amplifier" is just marketting!! Trying to get people to remember the good ol'days...

I'm also starting to suspect that most people who say that the distortion with germanium "sound better" had built a circuit designed for them , then replaced with silicon transistor without changes in the project... This is not fair!

I'm designing a distortion with a middle section like the Fuzz Face, or whatever, and with an input with a sinal conditioning, allowing us to set a pre-ampliication, and an off-set. this should give us much more control on the timbre then the usual circtuis... I hope I can reproduce the beloved good ol'days sound with this. another problem is that I never heard one of those stomp boxes with transistors picked by their precise values... Something I loathe!

It will be sad to me if I find out that this dependence on difficult-to-reproduce circuits is a necessity...
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Old 25th May 2007, 01:32 AM   #7
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actually the sound of a fuzzface is easier to duplicate using silicon jfets than it is to use germanium transistors. it's also going to be easier to find replacement transistors. the biasing is a bit different, but the actual distortion characteristics can be "modeled" into the jfet circuit much easier than doing it with silicon bjt's. it can also be done with op amps using a "log amp" feedback loop (yes, all of those chapters in the op amp books of "math functions" should not be skipped over.... they DO have their uses in audio)
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Old 25th May 2007, 02:00 AM   #8
NIC1138 is offline NIC1138  Brazil
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I just tried out a circuit with germanium transistors (AC188), and silicon (2N2222). I
moved around the collector resistor values up and down in both cases, and in the end I decided the best result was with the silicon transistors!...

But of course, I never heard a "real" fuzz face, so I can't say I know how it should sound.

I just made some simulations of the fuzz face circuit. I couldn't make it do a "smooth" distortion, as people usually claim it does. It just clips in the second stage, either by saturation, or by cutting. So, it's not smooth!...

How do we make "smooth" distortions?... I'm thinking about high voltage swing in a low gain second stage... Peraps this way we could perhaps see ad ifference between germanium and silicon... but then the differences between each transistor would show up too!
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Old 25th May 2007, 02:16 AM   #9
Minion is offline Minion  Canada
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Another interesting thing would be to also test Germainum and Silicon Diodes in Clipping stages, as Many Bipolar Transistor based Distortion curcuits will use Diodes to clip the signal and create that overdrive sound,

Others will use a fet and drive it into clipping to get Distortion or even some use a fet to overdrive a Mosfet.......There are many ways to use Transistors to create anything from a simple Boost up to a killer over the Top distortion......


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Old 25th May 2007, 04:33 AM   #10
lineup is offline lineup  Sweden
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Here's a schematic of
the original Germanium transistor version of the Dallas-Arbiter Fuzz Face:

Click the image to open in full size.

... from this site: http://www.theguitarfiles.com/guitarfile503.html

I did this simple Google search:
germanium fuzz schematic


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