Hey there!
Is anyone familiar enough with oscillators and changing old Germanium transistors for Silicon ones to make this child's play?

I've been trying to substitute 2n466 (fried by me) with 2n4399 or NTE180 (I have these in stock)
in a 12v inverter oscillator circuit.This is a popular old CDI unit sold by several entities.
This is the one that starts with an H (model cee pee 1060) that is slightly different than the Delta unit that has the schematic identified and available.
After weeks of searching, I was able to identify the exact schematic posted online with no specific ID.
I have tested all the components, and found them to be sound. At one point, I was able to get the oscillator to function with the 2n4399 by fudging the E to B resistance, now I can't. Was never able to keep it running consistently since I fried the original germaniums.
I know that this circuit is really simple to someone more familiar with oscillators.
I would like to get this CDI unit working soon so I can use it in my 1962 Chev step van.
The circuit should provide 300vdc to the coil. It provides awesome spark when it's working...but I blew it up. The xfrmr is tested good with outboard oscillator and scope. Have been temped to drive it with a 555. Want to take the simplest, most reliable approach.

 

Leave the 15Ω resistors alone. Change R1 to 470Ω 1W and R3 to 240Ω 2W. For R1 you could use the original R3.

 

I suck at oscillators, but this page might help you understand:
https://en.wikipedia.org/wiki/Royer_oscillator

 

Leave the 15Ω resistors alone. Change R1 to 470Ω 1W and R3 to 240Ω 2W. For R1 you could use the original R3.

Thanks!
I'll give that a try and post the results.
I'm pretty sure that's a givntakexchangepumplifier circuit. Yeah, that's it.

 

a givntakexchangepumplifier

LOL! That one's going right next to Armstrong and Colpitts oscillators.

 

I would replace the transistors for Npn MJE3055 types, and use a pushpull driven transformer with the bases on the others collectors, with Bemf diodes..

 

I think I would try to replace the PNP bipolar transistors with N-channel MOSFETs, and then make an oscillator to produce a set frequency to input to MOSFET drivers.

 

I would replace the transistors for Npn MJE3055 types, and use a pushpull driven transformer with the bases on the others collectors, with Bemf diodes..



View attachment 132680

The transformer is an integral (epoxied on) part of the PCB. Looks like a hockey puck stuck to the board. It works fine. It stays.
It was a very reliable circuit before I popped the germaniums. Just want to get the primaries pumping again.
Thanks.

 

The transformer is an integral (epoxied on) part of the PCB. Looks like a hockey puck stuck to the board. It works fine. It stays.
It was a very reliable circuit before I popped the germaniums. Just want to get the primaries pumping again.
Thanks.

Then replace the Nte180 transistors and make the R1,3 resistors 470 ohms 2W each, the 15ohms are just to turn off the transistors, The circuit is a poor design, asboth transistors can be on at the same time, my circuit diagram previously is a far superior performance as only one transistor can be fired at once, this design was used extensively in the 70/80s Sparkrite CDi systems.

 

I think I would try to replace the PNP bipolar transistors with N-channel MOSFETs, and then make an oscillator to produce a set frequency to input to MOSFET drivers.

That was a thought to use MOSFETs with a 555 driver.
I found that when testing the transformer with an oscillator, I was able to get quite a bit of gain difference by sweeping to higher freqs.
Not so sure if the rest of the circuit or the ignition coil would like the higher Hertz.
The thing is a great design. The spark increase that you can get with a standard (points) 12V auto ignition is phenomenal when you increase the coil voltage from 12 to 300VDC.

 

Then replace the Nte180 transistors and make the R1,3 resistors 470 ohms 2W each, the 15ohms are just to turn off the transistors, The circuit is a poor design, asboth transistors can be on at the same time, my circuit diagram previously is a far superior performance as only one transistor can be fired at once, this design was used extensively in the 70/80s Sparkrite CDi systems.

Are you saying to use the NTE 180's instead of the 2N4399's with the listed resistance?
I'll try and get downstairs to make the changes tonight.
I'm exited!
Thanks!

 

The circuit is a poor design

"Poor" is a relative statement for a design that worked so well for so long.
The thing brought me half way across the country and back without a problem.
I blew it up because I was careless when messing with it trying to make it more bullet proof. Doh!

 

Then replace the Nte180 transistors and make the R1,3 resistors 470 ohms 2W each, the 15ohms are just to turn off the transistors, The circuit is a poor design, asboth transistors can be on at the same time, my circuit diagram previously is a far superior performance as only one transistor can be fired at once, this design was used extensively in the 70/80s Sparkrite CDi systems.

I did a memory blunder. The NTE180's were from another project. Doh!
I MEANT NTE88! The 88's and 2n4399's are the only to3 PNP's that I have extras of.
Those resistances didn't work with the 88's or 4399's. Was hoping I could avoid spending money on it.
Is there an easy solution to get the 4399's or the 88's working in this circuit or are they both a bad choice?
Sorry about the boo boo.

 

It's hard to say since self-oscillating power circuits are tricky.

Since a silicon transistor has a 0.7 base emitter voltage drop while the germanium is 0.3, maybe try going to the other side of the bases and try increasing the 15 ohm bias resistors by a factor of 7/3 * 15. So maybe try replacing them with 36 ohm resistors and then keep the original 1k and 470 in the other two spots.

Maybe try temporarily adding some potentiometers in the bias circuits to try to more easily get bias points that get the oscillation going. In that case use care so as not to over-bias and overload the transistors.

 

It is possible the base windings do not have enough turns to run silicon transistors correctly. And it sounds like you cannot add turns as the transformer is potted.

 

It is possible the base windings do not have enough turns to run silicon transistors correctly. And it sounds like you cannot add turns as the transformer is potted.

I could isolate the primary side and take an inductance measurement if that would help. I think I already checked the resistance at around 15 ohms.
I was also wondering how much of the rest of the circuit has an influence on the oscillator. Would it still run if the secondary was open or shorted? I could make extra inductance but not if it needs to react with the other side of the transformer.
I found the 466 germaniums locally but that's $40 a pair. (better than $35 each on ebay) If I'm going to fork out money, I might as well spend $150 on a used MSD.
I appreciate all the help. I thought it might be a little easier.

 

If the secondary is shorted it probably will not run. Have you measured the rectifier diodes and other secondary stuff?

 

I did a memory blunder. The NTE180's were from another project. Doh!
I MEANT NTE88! The 88's and 2n4399's are the only to3 PNP's that I have extras of.
Those resistances didn't work with the 88's or 4399's. Was hoping I could avoid spending money on it.
Is there an easy solution to get the 4399's or the 88's working in this circuit or are they both a bad choice?
Sorry about the boo boo.

I would try the MJ2995 pnp T03 transistors, these are silicon so your resistors on the bases may need lowering..
Best option is to open circuit the secondary winding to the bridge rectifier, and replace the transistors and see if it's giving out AC 150/+ volts, then connect the rectifier back and check again for DC across the output capacitor.

 

I decided to build the basic circuit in the LTspice simulator and observed considerable variation in operation as I adjusted component values.

 

If the secondary is shorted it probably will not run. Have you measured the rectifier diodes and other secondary stuff?

Yes, I had to lift the diode that parallels the choke to test it. I've got one of those nifty semiconductor testers that identifies NPN, PNP, ECB, gain, etc.
I was such a doof. When I had it apart, I forgot to insulate the SCR and shorted it (poof). Replaced it with a beefier one (still worked), then promptly shorted that one and took out the germaniums. Doh!
I found the 2n4399's and tried them while sweeping a pot on the various front end resistors. I got it running by finding a tiny sweet spot, tried duplicating that resistance with a fixed resistor and haven't been able to get it running since.