germanium Preamp?

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#81
@tvicol

I'm interested in your version with GERMANIUM trasistor!! I'm a fan of Ge transistors, I asked many people in my country to make exactly what you do, but without any success... So, PLEASE, can you post me YOUR shematics?

my mail is germanijum@yahoo.com

thx

viccpa
 
#82

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#83
Sometimes I wish I could read Polish/ Chineese/ Japaneese/ Russian etc.....


In the diagram, The second transistor , T2/T4, does not have any bias.
I assume that it is a repeat of the first stage?

I also like the note re. operating temperatures !!!!!

Andy
 
#84
poynton said:
In the diagram, The second transistor , T2/T4, does not have any bias.
I assume that it is a repeat of the first stage?
Click to expand...

I wil try to translate the explanation...

Transistor bias is controlled trough inverted (polarization) capacitor, this way the operating “class” of germanium transistor is controlled by his current “leaking”…

Unlike Silicium transistors, this is posible with Germanium transistors, and works very, very well…
 
#85
bata bane said:


I wil try to translate the explanation...

Transistor bias is controlled trough inverted (polarization) capacitor, this way the operating “class” of germanium transistor is controlled by his current “leaking”…

Unlike Silicium transistors, this is posible with Germanium transistors, and works very, very well…
Click to expand...


😉
 
#89
Slightly OT.....

Is it a simple matter to substitute (replace for repair) an equivalent silicon device, for the old germanium device ?

I'm repairing some older test gear, and the germanium transistors are very hard to find.

(I am looking for some 2n508a, 2n1306, 1307 germaniums.....or modern silicon equivalents.)

thanks,
=RR=
 
#90
I have plenty of 2N1309 germaniums. Tested and guaranteed to be low leakage and with good gain. Top quality.

I also just bought a couple hundred AC128s but they have not arrived yet so I'm not sure how they will test out. The last AC128s that I bought were okay for leakage but low gain and I had to toss a lot of them when sorting, which is typical. :bawling:

http://www.muzique.com/

Best regards, Jack
 
#92
Would any of you say Germaniums are inherently "unreliable" and do you find they suffer from any changes in characteristics due to ageing etc if used correctly.
I have grown up with silicon, and apart from the first amp I ever made (which used AD149 outputs ) I have never used them seriously. There isn't much available now, so I guess it's all a bit academic, although I have a bag of "oldies" somewhere.
 
#93
Not really.

I built and modded several amps in the late '60s using OC35s and OC28s, including paralleled outputs in both transformer push-pull and quasi-comp.

I can only think of one instance where I had a problem. That was a 50watt disco amp which started to overheat and distort after 4 hours. The heatsink was too hot to touch - spit sizzled !!!!!! I backed the volume down a bit and put a fan across the HS.

Of course, any transistor in a glass case had to be watched as they are photocells if the black paint gets scratched. OC44/45 etc


I used all sorts from Mullard, GET even Uncle Clives magic rebrands

Andy
 
#94
Getting back to preamps...

Most old style germanium preamps followed a standard format....

no emitter resistor, collector resistor and a resistor from B to C.


I wondered recently, when this thread re-appeared, would there be any benefit in using a modern symmetrical, balanced, diamond approach ?????

I do not recollect seeing anything like this in germanium.

Anyone..........



Andy
 
#95
I remember the paint problem, in fact wasn't the OCP71 (was it ?) just an unpainted OC71. Funny things come back to you. The paint passes I/R radiation I think I remember reading. Some product/project can't remember now had a problem that was down to flourescent lights interfering with it. The cure was to shield an OC71 from light totally.
I have a GET101 I think it is somewhere ( in a very soft "copper" type metal case ) and assorted 2SA, 2N's etc and some BA ? numbers in a bakelight type material with yellow rubber sleeving over them. Happy days ?
 
#100
JBL SG520 Audio Amplifier

Netlist said:
That's an easy one:
JBL-SG520.pdf
Warning: 8.8 MB !!!
/ Hugo
Click to expand...
janneman said:
Hugo, I'll buy you a beer anytime we meet!
But you are right, maybe I should have more fun.
/ Jan Didden
Click to expand...

http://www.jblproservice.com/pdf/Vintage JBL-UREI Electronics/JBL-SG520.pdf
thanks, Netlist 😎

Lineup Audio LAB verdict:
JBL SG520 pre amplifier circuit
- Just great! Very High Quality, with today's standards,
.. eventhough being 'very old' amplifier.


See my detailed comments in circuit.
My Attachment, here below.
Enjoy 🙂
Lineup Audio Amp Reviews
.....
 

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