Popular Electronics, Feb. 1969

[WM6]

This is the genuine circuit diagram of "Miniature transistor metal detector" (see the PDF file in posting #7 by Qiaozhi or posting #42 by Technos).
Mike BG

Is K1 in form of Siemens B71701 too? I suppose it is ferrite pot?

Then what number of turns fall to K2 and K3, the same as K1, or K2 and K3 are factory made?

[mikebg]

Is K1 in form of Siemens B71701 too? I suppose it is ferrite pot?

Then what number of turns fall to K2 and K3, the same as K1, or K2 and K3 are factory made?

WM6,
Thе above circuit diagram with discrete transistors is too old to be copied. In modern circuits to avoid the use of inductive elements. For example K1 transformer serves to symmetry (avoids coils shielding) and impedance matching. It is not needed when using integrated circuit with a symmetrical input. Here's how the circuitry would look like in 70-years, when appears appropriate integrated amplifiers for audio frequency:

[WM6]

WM6,
Thе above circuit diagram with discrete transistors is too old to be copied. In modern circuits to avoid the use of inductive elements. For example K1 transformer serves to symmetry (avoids coils shielding) and impedance matching. It is not needed when using integrated circuit with a symmetrical input. Here's how the circuitry would look like in 70-years, when appears appropriate integrated amplifiers for audio frequency:

Agree mikebg, I do not like to see in schematic a lot of trafos.

But what do you mean, is it worth to upgrade this old schematic in some modern way without so much inductive coupling?

[Esteban]

I translate the schematic to Paint program and use the draft tool (4 sizes for different size of drawings). So you notice that lines cross here:

[mikebg]

The sensing head for mine detector MT-62

This is the sensing head for circuit diagram in posting #84:

[Esteban]

But this is not 60 years????

[mikebg]

The number means the year. There are 3 models in 60-ties: MT-60, MT-62 and MT-66. Above circuit diagram is of model MT-66.

[WM6]

The number means the year. There are 3 models in 60-ties: MT-60, MT-62 and MT-66. Above circuit diagram is of model MT-66.

Where do they get transistors in year 1960?

[holyuser]

Where do they get transistors in year 1960?

... from semiconductor factory, near sity of Botevgrad. Made under license of Thomson semiconductor ...

[WM6]

... from semiconductor factory, near sity of Botevgrad. Made under license of Thomson semiconductor ...

Thanks. Very intereseting. I thought that in Sixties were transistors still on the embargo list for Warsaw Pact.

[mikebg]

But this is not 60 years????

Esteban,
In 60 years there has been no digital voltmeters in Bulgaria.
Note that operating point voltages indicated in the circuit diagram (posting #84) are irreal because are measured by a primitive voltmeter, having low resistance. A modern voltmeter would show operating voltage near to Vbe = - 0,2 V, because transistors are made of germanium.

[mikebg]

Where do they get transistors in year 1960?

WM6,
The first model of family MT-60 is made of transistors bought by French company "Compagnie Generale de Telegraphe sans Fils" (shortly SANS FILS).
In the abbreviation of transistor type, letters SF mean "sans fils" (wireless). Note that there is a dot in transistor type; for example SF.T353. The Bulgarian made transistor is denoted as T353 only.

[WM6]

WM6,
The first model of family MT-60 is made of transistors bought by French company "Compagnie Generale de Telegraphe sans Fils" (shortly SANS FILS).
In the abbreviation of transistor type, letters SF mean "sans fils" (wireless). Note that there is a dot in transistor type; for example SF.T353. The Bulgarian made transistor is denoted as T353 only.

Maybe this explain something, even the late French President Charles de Gaulle decided to pull out of NATO's military command but in 1966, not 1960.

[mikebg]

Modification of HOUNDOG?

Is my idea of modernization of MT-66, shown in posting # 92 could be part of HOUNDOG modification?
REMI group was disappointed with me because I have no sense of reinventor.
I was very close to reinvent of HOUNDOG, publishing idea for its modification in posting # 92. I never thought to connect TX coil in above circuit diagram to output of LM386.
For me, sensors of MT-60, 62 and 66 are like the configuration shown in postings # 1 and # 8. Really RX coil of HOUNDOG has center tap and it can be split as TWIN LOOP.
My idea was to build for MT-66 a narrow band amplifier with LM386 working at 2500Hz. For that purpose I use a tank circuit L1-C2 having high Q-factor. However the modified HOUNDOG should work in a broad band at higher central frequency, for example 8KHz.
How should seems a modernized HOUNDOG?

[technos]

Bravo technos! Right decision. Maybe "REMI Group" cad do some help here by network analyzer?

Huh?? A network analyzer costs $1,200+ USD and I'm not in much of a mood to try and build one! But I am working on something in a little while. But I do not have much time the next couple of months!

Even though Esteban did a good job at finding some of the Popular Electronics 1969 article, it was missing some of the original bits. I found it on microfilm. A lot of these older articles are interesting reading!