5AHP7A Vintage SSTV The Deep image

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Re: 5AHP7A Vintage SSTV The Deep image

Postby Klaas Robers » Mon Feb 20, 2017 3:43 am

Harry, make the capacitors MUCH smaller. Think of 1 nF, 1000 pF. A capacitor of 470 uF will definively give the problems in scanning that you observe. This is for BOTH amplifiers (the part behind the 4k7 resistor). In fact they are the same amplifiers and there is no difference between line and field scanning.

In theory there is no capacitor needed at this point, but because the amplifier has feed back and the transistors have some delay, oscilation is a danger.

On the other hand, now the circuit diagrams are readable.... I see the final transistors should be AD161 and AD162. They are germanium transistors. How did you get these old transistors? They have a very small threshold voltage and as the circuit is, they cannot without any changes be replaced by modern silicium transistors. This is also a ground for the seen imperfections. However I think if you put much smaller capacitors in place, this also will help. Then the feed back loop is fast enough to mask any cross over problems.
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Klaas Robers
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Re: 5AHP7A Vintage SSTV The Deep image

Postby Harry Dalek » Mon Feb 20, 2017 6:09 pm

Klaas Robers wrote:Harry, make the capacitors MUCH smaller. Think of 1 nF, 1000 pF. A capacitor of 470 uF will definively give the problems in scanning that you observe. This is for BOTH amplifiers (the part behind the 4k7 resistor). In fact they are the same amplifiers and there is no difference between line and field scanning.


OH i see thanks so much Klass for looking at the problem .
i was just trying to follow the schematic as close as i could with junk box parts i had handy does not help when the schematic has faults i see theres a big change needed for the caps i will change as soon as i have some spare time again /

In theory there is no capacitor needed at this point, but because the amplifier has feed back and the transistors have some delay, oscilation is a danger.


I didn't understand this problem never really been explained till now i am very happy to know now...

On the other hand, now the circuit diagrams are readable.... I see the final transistors should be AD161 and AD162. They are germanium transistors. How did you get these old transistors?


They are replaced with what i had handy in my junk box ecg184 185 same as the bd184 185 my replacements are on the drawing schematic Yes old transistors are hard to get hold i tried to look for something similar.

They have a very small threshold voltage and as the circuit is, they cannot without any changes be replaced by modern silicium transistors. This is also a ground for the seen imperfections. However I think if you put much smaller capacitors in place, this also will help. Then the feed back loop is fast enough to mask any cross over problems.


Oh i see Klass very rare the Germaniums ,i will see how the caps go ..not sure if i have any Germanium power transistors.
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