My CTC-16XL Project.

[Yamamaya42]

I still can't decide which amp to go with, on the one side, the simple 2 transistor amp is cheap and easy, and SAYS it will boost to 3v ptp, but I'm a little worried that it also shows the output being at 4v dc, where the g1 voltage of the 1st video amp is 0v, I don't know if this will matter to the TV or not.
On the other hand, the lm359 , much more costly and complex,will take a bit to work out the programmable gain to get 3.5 v ptp out of it.

T_T
choices... choices...

[Electronic M]

Originally Posted by Yamamaya42

I still can't decide which amp to go with, on the one side, the simple 2 transistor amp is cheap and easy, and SAYS it will boost to 3v ptp, but I'm a little worried that it also shows the output being at 4v dc, where the g1 voltage of the 1st video amp is 0v, I don't know if this will matter to the TV or not.
On the other hand, the lm359 , much more costly and complex,will take a bit to work out the programmable gain to get 3.5 v ptp out of it.

T_T
choices... choices...

Why not just use a .1uF cap to couple the transistor amp output to the grid?..It will block DC from changing grid bias, should couple the video just fine and RCA colors all had some form of DC restoration that negates and need for DC video coupling in the early stages of the video chain.

[Yamamaya42]

simple 2 transistor amp was a failure,
spent a whole evening building it, but I'm getting very little gain out of it, not enough for what I need.

https://imgur.com/xYoNZOY

gonna have to try the op-amp version, and see if i get better gain out of it.

[old_tv_nut]

Can you give us a schematic of where you are connecting it in the set? If the amp is built right it should give the specified gain, but maybe not if you connect it to a point that loads it down.

[Yamamaya42]

Originally Posted by old_tv_nut

Can you give us a schematic of where you are connecting it in the set? If the amp is built right it should give the specified gain, but maybe not if you connect it to a point that loads it down.

I did not even attempt to hook it up, I looked at the wave on the scope and it was hardly 1.2v ptp out, unhooked to anything.
the goal is to have it hooked to Point B ( L9 ) test point one.
And i DID recheck the work, It just dud not put out 3v ptp

[old_tv_nut]

I think you should go back and check all the DC voltages on your amp. I have used this general design before and it worked. Then if you increase R7 to 470 ohms you should get a gain of 4x instead of 3x.

[Electronic M]

Could you have mixed up leads on your transistors?

[old_tv_nut]

Originally Posted by Electronic M

Could you have mixed up leads on your transistors?

Ditto. I did that on a magnetic tape preamp once. The transistor type had a reverse lead arrangement instead of the usual EBC sequence. As a result, all the stages were using the emitter as the collector and vice-versa. Instead of three stages with a total gain of 1000, I had three stages with a total gain of 3.

Another thing: I looked at that diagram and calculated the currents from the resistor voltages, and it looks like R5 must be 330 ohms, not 220, to get those voltages. Actually, I think it wouldn't hurt to increase R5 somewhat more than that, so that a larger proportion of the output current is supplied by T2.

[old_tv_nut]

One more thing - make sure you didn't read the omega symbol as a zero somewhere. The diagram is fuzzy. R7 is 330 ohms, not 3300, for example.

[Yamamaya42]

problem found, checking the DC voltages found that the cheap 12v power supply that i THOUGHT was regulated, is not. it says,"12v 100 ma " but hooked up, I was getting 16.5.
I hooked it up to adjustable pws and am getting much better results.

I'll just have to add a 7812 to the pcb to make it really stable.
thanks for everyone's help so far

[Yamamaya42]

output of V2 of the simple 2 transistor video amp, ( 7812 added )

https://imgur.com/xlQdL9t

output is through .1 uf,
will see how it works this weekend, I may have to up the gain a bit like old TV nut said, We shall see!

[old_tv_nut]

[Yamamaya42]

My only question is, once this is set up for perm, how should it be done? Directly TO g1 ( pin 7) of 1st video amp? ( L9 removed ) or through L9 to g1 with point 20 disconnected ?

[old_tv_nut]

L9 may be an IF choke, or it may be a peaking coil to match the detector to the grid capacitance, I don't know. Either way, it is not needed with the low output impedance of your amplifier. Plus, since your amplifier is a feedback circuit, hanging odd impedances on the output could pose a slight risk of high frequency oscillations. So, remove L9 and go through a coupling cap and then directly to G1, I think.

[old_tv_nut]

Note: my fingers stumbled all over my reply, I think I got it fixed up now, but reread it in case you saw the jumbled version.