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#151 luxo II

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Posted 26 February 2024 - 10:44 PM

I'm mildly surprised that it ever worked at all because if that diagram is correct, there will be spikes coming from the transformer coil (the centre tap is connected to the +12V side) onto the +12V rail and via the 2N3122 into the supply to the CMOS gates. 74xx chips are rated for only 18V and the spikes from that thing could easily exceed 30V or more - even with no load - and more than enough to make the CMOS misbehave or even fail completely.

 

Another aspect is that the timing Is based on a simple 555 R/C oscillator circuit. With a noisy power supply the timing will be pretty erratic so it was never going to run particularly stably.

 

Conclusion: it badly needs a few components to give the CMOS a stable supply isolated from the spiky output.

 

The basic ideas in this circuit are:

 

- the 555 timer is wired as an R/C oscillator, the timing set by R1, R2 and C1, You can look up a data sheet to see how that works.

 

- the 7473 flip-flop is wired to divide the frequency by two, and produce two identical square waves exactly out of phase with each other.

 

- the 7473 doesn't have the capacity to drive low-impedance loads (transistors) directly so a 7406 is used, with the outputs of three gates in parallel to drive a pair of transistors on one side of the transformer, and another three gates drive another pair of transistors on the other side.  The transistors are wired as high current-gain darlington pairs, with 4W 2.7 ohm resistors in series to limit the maximum current otherwise you'd exceed the thermal ratings of the transistors or the transformer, and have some rather hot, smelly smoke if you short-circuit anything.

 

The output circuit is symmetrical, in that the centre tap of the transformer primary is tied to +12V and one side or other of the winding should be energized alternately via the transistors. Since the components are the same and driven by the flip-flop, the timing of the square waves at the output should be quite exact - and symmetrical.

 

- the 0.27nF capacitor across the output is supposed to round off the top of the square waves, as in the yellow race. That you're setting the reverse in the blue trace suggests to me that one side of that capacitor has been connected to the frame, or to the centre tap. 

 

The oscilloscope traces show several things:

 

1. The blue trace and yellow trace are quite different. That implies something is quite faulty with the circuit. 

 

2. The yellow trace has a big spike at the leading (rising) edge of each pulse, which I would expect with a strongly inductive load (the transformer winding is an inductor) and the rounded top of the pulse shape is what I would expect. However, after the trailing (falling) edge of the pulse, there is a big spike a few milliseconds after, and this should not be seen and implies here is a fault somewhere in the CMOS circuitry driving the transistor pair.

 

3. The blue trace likewise has a big spike on the leading (rising) edge which is expected, but the shape of the pulse is wrong and indicates again something is wrong in the circuit as-built. Have you done something with the capacitor 0.27nF capacitor on the output side ?

 

Changes.

 

1. An LM7805 is just a 5V regulator and while you can use that to supply the 555 and 7473 logic gates, it won't fix really the above issues, there are other things wrong.

 

2. It needs decoupling (bypass) capacitors between the +12V and ground, and between the logic supply, at the emitter of the 2N3122 to ground, to stop the spikes reaching the CMOS. These should each include say 10 uF tantalum and 0.01uF ceramic.

 

3. I would replace the 7406 inverters with a simple pair of op-amps - eg LM 358 - wired as unity-gain voltage followers providing a much better buffer between the CMOS and the analog output.

 

4. Lastly beware of the output. Transformers being inductive the output spikes will be a lot more than 100 or 120V and quite enough to give you a painful shock if you make contact with bare wiring or terminals. Hazardous, actually.

 

Which is why ultimately I would put the whole thing in the trash - with the synchronous motor - and build a circuit to drive a 4V stepping motor which can be easily built and diagnosed at home with little more than a multimeter - and safely. Motors, drivers and more available at www.pololu.com. You could copy the 555 timer and the flipflops to drive a stepper driver. No transistors and no transformer required. The hardest part will be to choose a suitable stepping rate for nominal tracking, and tweaking the timer components to produce that frequency.


Edited by luxo II, 27 February 2024 - 03:07 AM.

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#152 deSitter

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Posted 27 February 2024 - 06:05 AM

I'm mildly surprised that it ever worked at all because if that diagram is correct, there will be spikes coming from the transformer coil (the centre tap is connected to the +12V side) onto the +12V rail and via the 2N3122 into the supply to the CMOS gates. 74xx chips are rated for only 18V and the spikes from that thing could easily exceed 30V or more - even with no load - and more than enough to make the CMOS misbehave or even fail completely.

 

Another aspect is that the timing Is based on a simple 555 R/C oscillator circuit. With a noisy power supply the timing will be pretty erratic so it was never going to run particularly stably.

 

Conclusion: it badly needs a few components to give the CMOS a stable supply isolated from the spiky output.

 

The basic ideas in this circuit are:

 

- the 555 timer is wired as an R/C oscillator, the timing set by R1, R2 and C1, You can look up a data sheet to see how that works.

 

- the 7473 flip-flop is wired to divide the frequency by two, and produce two identical square waves exactly out of phase with each other.

 

- the 7473 doesn't have the capacity to drive low-impedance loads (transistors) directly so a 7406 is used, with the outputs of three gates in parallel to drive a pair of transistors on one side of the transformer, and another three gates drive another pair of transistors on the other side.  The transistors are wired as high current-gain darlington pairs, with 4W 2.7 ohm resistors in series to limit the maximum current otherwise you'd exceed the thermal ratings of the transistors or the transformer, and have some rather hot, smelly smoke if you short-circuit anything.

 

The output circuit is symmetrical, in that the centre tap of the transformer primary is tied to +12V and one side or other of the winding should be energized alternately via the transistors. Since the components are the same and driven by the flip-flop, the timing of the square waves at the output should be quite exact - and symmetrical.

 

- the 0.27nF capacitor across the output is supposed to round off the top of the square waves, as in the yellow race. That you're setting the reverse in the blue trace suggests to me that one side of that capacitor has been connected to the frame, or to the centre tap. 

 

The oscilloscope traces show several things:

 

1. The blue trace and yellow trace are quite different. That implies something is quite faulty with the circuit. 

 

2. The yellow trace has a big spike at the leading (rising) edge of each pulse, which I would expect with a strongly inductive load (the transformer winding is an inductor) and the rounded top of the pulse shape is what I would expect. However, after the trailing (falling) edge of the pulse, there is a big spike a few milliseconds after, and this should not be seen and implies here is a fault somewhere in the CMOS circuitry driving the transistor pair.

 

3. The blue trace likewise has a big spike on the leading (rising) edge which is expected, but the shape of the pulse is wrong and indicates again something is wrong in the circuit as-built. Have you done something with the capacitor 0.27nF capacitor on the output side ?

 

Changes.

 

1. An LM7805 is just a 5V regulator and while you can use that to supply the 555 and 7473 logic gates, it won't fix really the above issues, there are other things wrong.

 

2. It needs decoupling (bypass) capacitors between the +12V and ground, and between the logic supply, at the emitter of the 2N3122 to ground, to stop the spikes reaching the CMOS. These should each include say 10 uF tantalum and 0.01uF ceramic.

 

3. I would replace the 7406 inverters with a simple pair of op-amps - eg LM 358 - wired as unity-gain voltage followers providing a much better buffer between the CMOS and the analog output.

 

4. Lastly beware of the output. Transformers being inductive the output spikes will be a lot more than 100 or 120V and quite enough to give you a painful shock if you make contact with bare wiring or terminals. Hazardous, actually.

 

Which is why ultimately I would put the whole thing in the trash - with the synchronous motor - and build a circuit to drive a 4V stepping motor which can be easily built and diagnosed at home with little more than a multimeter - and safely. Motors, drivers and more available at www.pololu.com. You could copy the 555 timer and the flipflops to drive a stepper driver. No transistors and no transformer required. The hardest part will be to choose a suitable stepping rate for nominal tracking, and tweaking the timer components to produce that frequency.

Even with my limited understanding of electronics I understood this. Thanks! The conclusion made me smile.

 

-drl



#153 DAVIDG

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Posted 27 February 2024 - 09:03 AM

 Well the Saxon circuit was published in Jan 1975 Sky and Telescope  and I would say a couple hundred have been made if not more.  I have also seen many other design that are very similar to the Saxon circuit including many commercial drive corrector from that time. Willman Bell sold a kit with a circuit board to make assemble easier so. I build one myself and it has worked perfectly since then. I have over 40 years in electronic design  experience and when it was designed using the parts  available it is well done.

   Vintage telescope uses  AC synchronous motors that work VERY well. So  one would have to reengineer the drive to take a stepper and then built the controller. For some  vintage scopes that would be difficult  and also reduce the value.  For the Criterion Dynamax 8 which the drive corrector is being discussed it uses two  AC synch motor are running at 1 Revolution per Hour. So to use a stepper would require finding   two stepper  of correct footprint to fit the mount and that also have gear box to reduce the step size so even when micro-stepped  the step size would be small enough not to be seen in the eyepiece. Do able yes but it takes and understanding of both electronics and mechanics.  The results would be that you can run it the scope on  a battery and change the speed but that is what  a DC/AC drive corrector allows you to do . So I don't agree with statement " Which is why ultimately I would put the whole thing in the trash - with the synchronous motor"  at all and the simpler solution is to use a DC/AC inverter or built a DC/AC drive corrector. 

 

                      - Dave 


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#154 Goofyboy1

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Posted 28 February 2024 - 12:43 AM

I'm mildly surprised that it ever worked at all because if that diagram is correct, there will be spikes coming from the transformer coil (the centre tap is connected to the +12V side) onto the +12V rail and via the 2N3122 into the supply to the CMOS gates. 74xx chips are rated for only 18V and the spikes from that thing could easily exceed 30V or more - even with no load - and more than enough to make the CMOS misbehave or even fail completely.

 

Another aspect is that the timing Is based on a simple 555 R/C oscillator circuit. With a noisy power supply the timing will be pretty erratic so it was never going to run particularly stably.

 

Conclusion: it badly needs a few components to give the CMOS a stable supply isolated from the spiky output.

 

The basic ideas in this circuit are:

 

- the 555 timer is wired as an R/C oscillator, the timing set by R1, R2 and C1, You can look up a data sheet to see how that works.

 

- the 7473 flip-flop is wired to divide the frequency by two, and produce two identical square waves exactly out of phase with each other.

 

- the 7473 doesn't have the capacity to drive low-impedance loads (transistors) directly so a 7406 is used, with the outputs of three gates in parallel to drive a pair of transistors on one side of the transformer, and another three gates drive another pair of transistors on the other side.  The transistors are wired as high current-gain darlington pairs, with 4W 2.7 ohm resistors in series to limit the maximum current otherwise you'd exceed the thermal ratings of the transistors or the transformer, and have some rather hot, smelly smoke if you short-circuit anything.

 

The output circuit is symmetrical, in that the centre tap of the transformer primary is tied to +12V and one side or other of the winding should be energized alternately via the transistors. Since the components are the same and driven by the flip-flop, the timing of the square waves at the output should be quite exact - and symmetrical.

 

- the 0.27nF capacitor across the output is supposed to round off the top of the square waves, as in the yellow race. That you're setting the reverse in the blue trace suggests to me that one side of that capacitor has been connected to the frame, or to the centre tap. 

 

The oscilloscope traces show several things:

 

1. The blue trace and yellow trace are quite different. That implies something is quite faulty with the circuit. 

 

2. The yellow trace has a big spike at the leading (rising) edge of each pulse, which I would expect with a strongly inductive load (the transformer winding is an inductor) and the rounded top of the pulse shape is what I would expect. However, after the trailing (falling) edge of the pulse, there is a big spike a few milliseconds after, and this should not be seen and implies here is a fault somewhere in the CMOS circuitry driving the transistor pair.

 

3. The blue trace likewise has a big spike on the leading (rising) edge which is expected, but the shape of the pulse is wrong and indicates again something is wrong in the circuit as-built. Have you done something with the capacitor 0.27nF capacitor on the output side ?

 

Changes.

 

1. An LM7805 is just a 5V regulator and while you can use that to supply the 555 and 7473 logic gates, it won't fix really the above issues, there are other things wrong.

 

2. It needs decoupling (bypass) capacitors between the +12V and ground, and between the logic supply, at the emitter of the 2N3122 to ground, to stop the spikes reaching the CMOS. These should each include say 10 uF tantalum and 0.01uF ceramic.

 

3. I would replace the 7406 inverters with a simple pair of op-amps - eg LM 358 - wired as unity-gain voltage followers providing a much better buffer between the CMOS and the analog output.

 

4. Lastly beware of the output. Transformers being inductive the output spikes will be a lot more than 100 or 120V and quite enough to give you a painful shock if you make contact with bare wiring or terminals. Hazardous, actually.

 

Which is why ultimately I would put the whole thing in the trash - with the synchronous motor - and build a circuit to drive a 4V stepping motor which can be easily built and diagnosed at home with little more than a multimeter - and safely. Motors, drivers and more available at www.pololu.com. You could copy the 555 timer and the flipflops to drive a stepper driver. No transistors and no transformer required. The hardest part will be to choose a suitable stepping rate for nominal tracking, and tweaking the timer components to produce that frequency.

I used the original criterion’s hand controller and inverter. 
I cut out the 230Vac 50Hz eu input and want only use the 12Vdc input too keep it simple.

 

in the hand controller got about 10,8V and feed the C2001’s and C1815’s. My leg is I haven’t any electronica experience but won’t too fix my Criterion Dynamax telescopes clock drive.

 

does C2001 and C1815 10,8 Voltage or can I put the LM7805cv at the input side off the hand controller?

from what I understand from the data sheets the C1815 can handle 50V and the C2001 30V and both the base needs a 5V source. So from my point of view I can send a 5V voltage wat into the hand controller by add the LM7805 inside the inverter unit instead in the hand controller because there is little free space.

 

for Diagnostic I hooked up my power supply too the hand controller @ 8V too the lm7805 and removed the zener diode 6.2v rated. But the problem is when I hooked the LM7805 between the input and the hand controller it doesn’t work but it doesn’t work if I connect the LM7805 on the 10,8 trace on the hand controller..

 

so LM7805 on the -12V side hand controller LM7805 on the 10,8v in put side off the moederboard I connected the in put voltages and the 5V I connected too the bottom rail where the zener was connected. 
 

what I trying I did not get 5V on the C2001 emitter the left leg. Also I didn’t measure 60Hz.

 

on my hand controller the +12V in only switching on or off by the potential meter and the -12V is connecting too the 50K ohm potential pot for adjustment.

 

ehy o why doesn’t it work for me?



#155 luxo II

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Posted 28 February 2024 - 03:53 PM

@David, That's fine for you - you clearly have the knowledge to build and diagnose issues with the circuit, and do it without causing electrostatic damage to the CMOS, nor getting hurt.

 

But Goofy lacks that competency, and I personally would never recommend a noob open and tinker with a boxful of birds-nest wiring producing lethal voltages. Sorry Goofy, I don't do remote circuit diagnosis by telepathy, either.

 

Yes Goofy probably could build a simple circuit from scratch, with a fair chance of success, but I'd only suggest that where he has PCB with an intelligible layout and artwork and the voltages are safe (ie under 50V) - hence why I would start with a simple 7805 and 555 oscillator, get that to work, then connect that to a stepper driver and motor. And yes it does involve some maths, but after all electronics and astronomy are both heavily dependent on maths if you want to design stuff well.

 

NB instead of the simple 555 timer circuit, when I was building drives decades ago my preference was to use an opamp voltage-to-frequency circuit. A simple potentiometer could be used to set speed (a wire-wound one worked nicely) and in addition the slew pushbuttons would ramp the voltage up and down, achieving smooth acceleration/deceleration for slewing. A quartz oscillator with a frequency divider was even better, but these days using a microprocessor and some code is simpler hardware-wise.


Edited by luxo II, 28 February 2024 - 04:21 PM.


#156 Goofyboy1

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Posted 29 February 2024 - 03:53 AM

Hi Luxoll,

I understand your point of view but the problem is still that I can use my scope and will beginning start this hobby and enjoying the skies with their planet’s.

if you scroll back you can see and follow the problem and I have post photos from the inverter unit and the criterion hand control. Because it’s over 40 years old technics I have/had the problem that the traces on the motherboard has cracks and needed thin wires to repair it. Maybe I overheated components by repairing the traces. The problem then is that I have a bunch of old electronic trash that I can use for spare parts. But then which replacement can I use for the green capacitors and which can I replace for the SC2001 & SC1815 transistors 🤔.
I have already new NPN transistors D315 placed and new wiring in the inverter that corresponds modern colours. Red for positive and black for negative. This makes it easier for understanding the layout for me and eventually the next owner if needed.

a question, on many online schematics is see that diodes are used for power regulation soo the hardware is protected for overcurrent. Because I’m decided to only use if the 12V input and removed the 220Vac 50Hz 12Vdc transformer I want a  power protection. What is the best option too do this?

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#157 Goofyboy1

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Posted 29 February 2024 - 04:07 AM

Transistor D315, C2001 & C1815 has a base Voltage of 5V. Now the 12v will reduced by 40 ohm resistor inside the inverter so the voltage will drops to 10.x V and it will feed the hand controller. The 10K ohm potential switch is used for switching on or off and for controlling the motors speed. The 50K ohm potential meter for tweaking the frequency. Does the transistors need that higher 10.x V input or can I put the lm7805 between the inverter and hand controller?



#158 fullthrottle_man

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Posted 29 February 2024 - 11:37 AM

Just out of curiosity, why are you concerned about getting the drive corrector system working? I've never used my drive correctors on mine, I just plug the telescope base straight into an extension cord and it tracks just fine as long as I do a good alignment and level...

#159 DAVIDG

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Posted 29 February 2024 - 01:15 PM

 Here is what you need to check.  You should have between 8  to 12 volts coming up to  the hand controller. That gets reduced to about 6 volts at the Zener.  The c2001 transistors are what is controlling the power transistors down in the main box.   Since you only have a volt meter but it does have a frequency setting at the emitters of each of the C2001 transistors you should measure around a 60hz frequency at about 1 to 3 volts. See  post 107  and my picture showing the waveform I'm measuring at the emitters of C2001. That frequency should change as you turn the pot on the hand controller and also change when you push the FAST and SLOW buttons. The FAST button should give you about 70 HZ and the SLOW about 50 HZ.   If hand controller does not work like I descripted detach the connection from the hand control to the bases of D315 power transistor and see if does behave like it should. If it does the problem has something to do with the power transistor. If is doesn't then the problem is in the hand controller.   If the problem is in the hand controller then it is most likely one the transistors is bad , or one of the two pots is bad  There is also the possibility that the controller was assembled wrong. I believe Gil V who actually worked at Criterion made a statement at one time that many of this units never worked from  the start. 

   The unit should run with the 6.2 volt zener. The reason why I replaced it with LM7805 is because that is just a more stable voltage regulator and I happen to have box of them. So you have to get the oscillating circuit in the hand controller to work to get the rest of the controller to work.  

 

                        - Dave 


Edited by DAVIDG, 01 March 2024 - 11:53 AM.


#160 Goofyboy1

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Posted 29 February 2024 - 02:32 PM

Just out of curiosity, why are you concerned about getting the drive corrector system working? I've never used my drive correctors on mine, I just plug the telescope base straight into an extension cord and it tracks just fine as long as I do a good alignment and level...

Because in the EU there is no 110V 60Hz but 220V 50Hz. 
 



#161 fullthrottle_man

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Posted 29 February 2024 - 05:56 PM

Because in the EU there is no 110V 60Hz but 220V 50Hz.


Ah ok. That makes sense then.

#162 Goofyboy1

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Posted 12 March 2024 - 03:12 AM

Very little update. 
 

after desoldering the hole hand controllers motherboard and resoldering I got 60 hz but when i hooked up the mean unit and saw it works I placed a resistor between the emitters and the negative. After this one D315 transistor got warm and the hole units fails. 
 

after removing the resistor between the emitter and negative it stills fails.

 

I placed the LM7805 between the power in and the hand controller. 
 

I’m wondering if it’s wise too split the positive after the resistor that drops down the voltage before the hand controller also connecting too the positive side off the transformer.



#163 Gil V

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Posted 12 March 2024 - 07:55 PM

There has to be a better way.


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#164 deSitter

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Posted 12 March 2024 - 08:39 PM

There has to be a better way.

The immortal words of George Westinghouse, and Bubba McStump the shade-tree mechanic.

 

-drl



#165 Goofyboy1

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Posted 13 March 2024 - 10:37 AM

Can someone explain me why the “Min” voltage is -2.70V?

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#166 DAVIDG

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Posted 13 March 2024 - 11:40 AM

.  Are your measuring with the hand controller connected to the main unit or not ? If so then I would measure the waveforms with it being not connected. That will tell you if the spike is coming from feedback from the power transistor/transformer or some problem with the timing circuit itself.  The other possibility is were you choose to attach the oscilloscope probe to "ground" . If your not at true ground   

 

 

                       - Dave 



#167 Goofyboy1

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Posted 13 March 2024 - 12:26 PM

Hi Dave,

 

its a strange thing. If I disconnect the mean unit I can’t get its stable and not at 60Hz but when I connect it then I can 60Hz



#168 DAVIDG

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Posted 13 March 2024 - 01:47 PM

  The only thing I can think of is that  you don't have a good ground and it getting a ground through the power transistors. So I would totally disconnect the hand controller from the main unit and power it at about 8 volts from an  independent power supply and see what happens.  You  have to  get the  hand  controller circuit working correctly independent of the  main unit.

 

             - Dave 



#169 Goofyboy1

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Posted 13 March 2024 - 03:50 PM

Housten we have solved te problem!



#170 Goofyboy1

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Posted 14 March 2024 - 02:29 AM

Hello everyone,

 

After I got it fixit for now I’m wondering how I can let drop the voltages on the transformer side so it will fixit @ 100V 60Hz. 
Does anyone a good idea?

 

Could I use a LM7810 too drop it down too 10V?



#171 DAVIDG

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Posted 14 March 2024 - 10:25 AM

 You need to drop the voltage going to  the collectors of the power transistors. The transformer in mine unit has secondary winding that is for 10 volts and the primary is 120 volts so amplification of 12:1. Remember that AC voltage is measured in RMS ( root mean square) and your test equipment usually measures Peak to Peak.  So 120 volts AC RMS will measure as 1.414 x 120 volts or about 170 volts peak to peak.  Since  the transform in mine  has 12:1 amplification  and I input 12 volts and not 10. I'll get more then 120 volts RMS. So you need to drop the voltage going into transformer down to 10 volts. Dropping the voltage to hand controller won't work it has to be the voltage going the transformer.   You can use a voltage regulator  like an LM7810 BUT you need to be sure it can supply the needed current. The small T0220 case types are good to about a max of 1.5 Amp and need to be attached to a heat sink and your operating close to the maximum rating so not good .  I would use one that is metal can TO-3 case that is mounted on heat sink and those type can handle 3 amp or more. 

   The reason why these unit are making more voltage then the common 120 volts AC RMS is that they were designed in 1970's and in Japan. Both in the US and in other countries the AC voltage use to be lower then the standard today. In the US is more like 110 volts and sometimes even lower.

 

                           - Dave 



#172 Goofyboy1

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Posted 14 March 2024 - 11:21 AM

Oke it’s clear to me!

I have ordered new transistors and capacitors because after yesterday it works nice today it was warmer inside and the frequency gone all over te scale. 



#173 AlMuz

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Posted 21 April 2024 - 02:05 AM

Joining the club with my find on Facebook Marketplace this week in Burlington, MA

Golden Pyramid Tripod was a thing of beauty which cought my eye

 

Original asking price was $400.

I am not new to rebuilding classic scopes but I was new to Criterion SCTs.
After looking it up I did share details about the reputation of these scopes with seller and we agreed on $250.

 

Serial number (on the clock drive): 4916
The full Golden Pyramid Setup - Pic 2

 
The scope also came with 50 mm finder and its mounting rings (awful quality - made by pouring molten metal into a sand form).
Very dirty and moldy 30 mm ASP eyepiece and 1.25" diagonal.
A manual and probably original shower-cap.
 
There is no serial number on corrector mounting ring. 
Corrector plate itself is a bit moldy on inside, but should be easy clean.
It also slides sideways by 4..5  mm when I tilting the scope onto another side of the fork (needs some shimming on perimeter).
 
Full gallery:
Pandora Box
Album: Criterion Dynamax 8
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Overall for something older than me it is in a great shape. 
Time to clean, re-collimate and see what it can do

Edited by AlMuz, 21 April 2024 - 02:14 AM.

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#174 fullthrottle_man

fullthrottle_man

    Vostok 1

  • -----
  • Posts: 165
  • Joined: 01 Sep 2023

Posted 21 April 2024 - 07:50 AM


Joining the club with my find on Facebook Marketplace this week in Burlington, MA
Golden Pyramid Tripod was a thing of beauty which cought my eye

Original asking price was $400.
I am not new to rebuilding classic scopes but I was new to Criterion SCTs.
After looking it up I did share details about the reputation of these scopes with seller and we agreed on $250.

Serial number (on the clock drive): 4916


The scope also came with 50 mm finder and its mounting rings (awful quality - made by pouring molten metal into a sand form).
Very dirty and moldy 30 mm ASP eyepiece and 1.25" diagonal.
A manual and probably original shower-cap.

There is no serial number on corrector mounting ring.
Corrector plate itself is a bit moldy on inside, but should be easy clean.
It also slides sideways by 4..5 mm when I tilting the scope onto another side of the fork (needs some shimming on perimeter).

Full gallery:


Overall for something older than me it is in a great shape.
Time to clean, re-collimate and see what it can do


That's in beautiful shape! Same color scheme as my good one, so it was built 1978 or later. Judging by the base plate number, it seems to be pretty late in the run, but others know more than I do about that. I'm sure you're aware of marking the corrector plate before removing so you can put it back in the same orientation? Mine does good on low and medium powers. Once I try pushing the magnification past about 200x (10mm eyepiece) it starts to get very soft focus. Admittedly, I don't have the collimation on mine perfect yet. But I haven't had it out in a couple months either. I'm very curious how well yours performs after you're finished.
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#175 davidc135

davidc135

    Gemini

  • *****
  • Posts: 3,283
  • Joined: 28 May 2014
  • Loc: Wales, UK

Posted 21 April 2024 - 08:41 AM

 

Joining the club with my find on Facebook Marketplace this week in Burlington, MA

Golden Pyramid Tripod was a thing of beauty which cought my eye

 

Original asking price was $400.

I am not new to rebuilding classic scopes but I was new to Criterion SCTs.
After looking it up I did share details about the reputation of these scopes with seller and we agreed on $250.

 

Serial number (on the clock drive): 4916

 
The scope also came with 50 mm finder and its mounting rings (awful quality - made by pouring molten metal into a sand form).
Very dirty and moldy 30 mm ASP eyepiece and 1.25" diagonal.
A manual and probably original shower-cap.
 
There is no serial number on corrector mounting ring. 
Corrector plate itself is a bit moldy on inside, but should be easy clean.
It also slides sideways by 4..5  mm when I tilting the scope onto another side of the fork (needs some shimming on perimeter).
 
Full gallery:


Overall for something older than me it is in a great shape. 
Time to clean, re-collimate and see what it can do

 

That's a great deal for $250. If only the views are as good as the looks.  David


  • AlMuz likes this


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