Stabistor circuit

[tom42107]

New guy here, trying to figure something out. I came across a schematic in a book I bought at the flea market the other day and I would like to play around with it. Very basic circuit, transistors, resistors, diodes and a couple of caps. Takes a + and - 6 volts. Since it's from the 60's, some of the part numbers are not coming up well with a google search. Here they are:

SG22 diode
2N541 transistor
2N478 transistor

I believe these were made by the Transitron company. I did find a .pdf of the data for these parts, but I don't think it's as easy as matching them up with modern day parts and dropping them in, but again, I'm really new to this. Quoting from the book, "Stabistor DC coupling eliminates the need for large bypass capacitors or excessive bleeder current. Stabistor coupling also fixes the collector-to-emitter voltages at a low value, about 1 volt. It goes on to say that the stabistor diodes prevents damage to the base-to-emitter junction by any excessive negative signal.
Here is the .pdf info that I found:


                PWR. BV    BV    Hfe        Ic Vce  Vce  Ib  Ic  Fr  Icbo Vcb    Icbo  Vcb
                Diss.  cbo  ceo  min-max            (sat)  MA MA mc    uA  volts  uA
                mW  volts volts                        volts                  25C          150C
               
2N478  NPN  200  15    15    40  100  1  5    1.5  2.2  5  8    0.5  50    15    15    TO-5
2N541  NPN  200  15    15    80  200  1  6    1.5  2.2  5  10  0.5    50    15    __    TO-5

SG22:

Max Forward Voltage  Forward    Reverse  Reverse    Power
          Volts            Current    Current    Voltage    Dissipation
                                MA        uA 25C      Volts        mW
.47 min./.53 max.        .25              .1          2            250
.52 min./.60 max.          1
.64 min./.72 max        .10 
.67 min./.77 max        .20
      .64+/-10%
          1                    100

Based off of this information, do you think there are modern replacements or is there not enough circuit information to determine.
I just started getting into the DIY stuff. Hope it's not to late to start learning. Thanks.

Tom

 

[PRR]

Stabistor is a low-voltage reference diode. "Zener" is correct above ~~7V; below 5V our "zeners" really use a different mechanism.

It appears your part is a tightly specified simple -forward- diode. Put in a 1N400x rectifier.

It will really help to _understand_ the circuit before you build it. Random pluckings from past books are sometimes hit-or-miss... they work with the part the author had in hand but have no tolerance for variation. OTOH sometimes published circuits are quite un-critical. It might be good to say what book, even post a clip. (If it is a TAB book, 99% of those were garbage.)

A 2-transistor amp can, today, be built fine without diode coupling. However if we believe the specs you cite for those NPNs, you might need a diode to buck the 1.5Vce spec. Modern NPNs have Vce at 5mA or 50mA more like 0.1V-0.2V, not 1.5V. So you may be studying something of little use today.

 

[tom42107]

Your right about needing to understand the circuit. I thought it looked pretty simple to breadboard and play around with, to help start the learning process. The book is a Howard Sams, published in 1963. I went ahead and drew out the schematic. As far as the specs on the diodes and transistors, I took them right off the Transitron company pdf that I found.

 

[tom42107]

Sorry about the big size. This one's smaller.

 

[PRR]

Surely Q1 collector (feeding Q2 base) is not connected directly to +6 Volts?

Without resistor values, it is hard to say anything else. Except with a more-likely connection of Q1 collector, the input impedance is zero. So it fits into something else: a mixer, a servo-amp, a DAC.... something where gain is defined by input current not input voltage.

The intent of those added diodes is to raise collector-emitter voltages. Old transistors got soft below 1V. Modern ones don't. The diodes are not needed.

Cocktail-napkin then breadboard this. It is the same amp for modern transistors.

 

[tom42107]

Thanks PRR, your totally right. I left off a resistor when I redrew the schemo. Here it is again with the added resistor and values,(which were in another part of the book). It says it has a gain of 44db with a 50K source and load, frequency response of 4-100K at the 3-db point. Cinemag has a 37.5,150,600:50k. Could this make a mic pre or is it to low gain?

 

[rafafredd]

That transformer can give you almost 25db (considering some loss). With 44db electronic gain, you could have a mic pre of almost 70dB gain. That's a lot! But headroom will be poor, at +-6v rails.

 

[PRR]

> headroom will be poor, at +-6v rails.

No, just one 6V rail powers the output. The neg 6V rail is only used for a small amount of bias. That's another sign that they are fixing problems that we just do NOT have now, not since the early 1960s. (And even in the early 60s, there were better ways.)

> It says it has a gain of 44db with a 50K source and load

Worded poorly. This does not mean the input is 50K. It means the external source must have 50K impedance. The input impedance looking-into C1 is about 400 ohms. (The left-most C1, 15uFd; you have another C1 0.001u.)

> frequency response of 4-100K at the 3-db point.

Very possible. With somewhat better parts, my sim showed some peaking at 3MHz. The 0.001u appears to load things down at 3KHz. It may rolloff at 100KHz, or it may be their test didn't go above 100KHz.

> Cinemag has a 37.5,150,600:50k

The load on the 150 ohm mike would be about 1 ohm plus winding loss, probably 20 ohms of which 19 ohms is dead loss.

You could connect a dynamic mike (SM57) right to the 15u C1. It would work. Maximum output in modern loads would be barely 1V. Gain might be as high as 80db.... the amp is NOT intended for low-impedance sources.

I'm not sure what it is good for? I have done something like it (without the silly Stabistors and negative bias) but MUCH simpler yet stronger. Something like the plan in my post (#4). If the negative rail is handy, the "470K" should maybe be 390K. Better: change the "1Meg" to 100K and return it to ground. That sets Q3 collector to 6 times Q1 base, around 3V which is fine for 6V supply.

> Cinemag has a 37.5,150,600:50k. Could this make a mic pre

Do you want a tutorial or a mike preamp? Get the CineMag and a TLO72 and wire it up gain of 10 (1 to 50). Fine basic studio preamp.