I acquired my Wavetek 166 signal generator about 20 years ago. I really like knobs and have avoided digital for this reason.
It worked great for the first five then it went belly up. - no signal output. I use this generator frequently. I had transported it and it didn't travel well apparently.
I affectionately call this my "analog nightmare". It's design preceded all but the 741 op amp. There's a ton of discrete circuitry as a result.
The design concept is sound and used in many generators of that period. Essentially all waveforms are generated from a self oscillating triangle waveform generator circuit. A positive and negative current source pair alternately charge and discharge a selected capacitance. This results in a very linear ramp up and down at the frequency dictated by the current level and capacitance.
Anyway, there's a buffer circuit that follows the triangle generator implemented with a matched pair of FETs, a matched pair of BJTs, and misc components numbering in the neighborhood of 25. This circuit has been the bain of me.
I fixed it the first time by replacing the two seperate FETS with a dual matched pair package, 2N5564. I had to fly wire the second half to the land pattern of the second FET next to the first. This worked great for about 8 years of hard use.
It broke again lately. This time it puts out a distorted signal rather than none at all. The triangle wave looks scalloped symmetrically on the rise and fall.
It's black and white. The signal looks perfect before the buffer and distorted after. The triangle signal from the generator needs to be buffered by a very high input Z circuit hence it hits the gate of one of the JFETS. I replaced the matched pair again - no change.
After a ton of head scratching I decide to simulate it in TINA to get an idea what might be going on. It simulates great in TINA with expected result. However, it takes about 30 seconds of iteration to come with a DC operating point. This exercise yielded no fruit ultimately.
Hmmmm.... is the output of the buffer being overloaded?
Well, normally I would unhook the output to prove that. Unfortunately, the buffer is a part of a big loop and triangle circuit stops producing a waveform.
I replaced a few other transistors - no change. Replacing anything is quite difficult. To get to the solder side one must remove another board that covers up the board of interest. This includes removal of many knobs, etc. I suppose I could replace all components (25) comprising the buffer circuit. However buying enough transistors so I can match them seems insurmountable.
I threw my hands up and now have decided to build a buffer using a high speed JFET opamp and will splice it in. That's really quite simple now that High input Z, high speed, high V op-amps are available.
I'll let you know the results in a week or two.
It worked great for the first five then it went belly up. - no signal output. I use this generator frequently. I had transported it and it didn't travel well apparently.
I affectionately call this my "analog nightmare". It's design preceded all but the 741 op amp. There's a ton of discrete circuitry as a result.
The design concept is sound and used in many generators of that period. Essentially all waveforms are generated from a self oscillating triangle waveform generator circuit. A positive and negative current source pair alternately charge and discharge a selected capacitance. This results in a very linear ramp up and down at the frequency dictated by the current level and capacitance.
Anyway, there's a buffer circuit that follows the triangle generator implemented with a matched pair of FETs, a matched pair of BJTs, and misc components numbering in the neighborhood of 25. This circuit has been the bain of me.
I fixed it the first time by replacing the two seperate FETS with a dual matched pair package, 2N5564. I had to fly wire the second half to the land pattern of the second FET next to the first. This worked great for about 8 years of hard use.
It broke again lately. This time it puts out a distorted signal rather than none at all. The triangle wave looks scalloped symmetrically on the rise and fall.
It's black and white. The signal looks perfect before the buffer and distorted after. The triangle signal from the generator needs to be buffered by a very high input Z circuit hence it hits the gate of one of the JFETS. I replaced the matched pair again - no change.
After a ton of head scratching I decide to simulate it in TINA to get an idea what might be going on. It simulates great in TINA with expected result. However, it takes about 30 seconds of iteration to come with a DC operating point. This exercise yielded no fruit ultimately.
Hmmmm.... is the output of the buffer being overloaded?
Well, normally I would unhook the output to prove that. Unfortunately, the buffer is a part of a big loop and triangle circuit stops producing a waveform.
I replaced a few other transistors - no change. Replacing anything is quite difficult. To get to the solder side one must remove another board that covers up the board of interest. This includes removal of many knobs, etc. I suppose I could replace all components (25) comprising the buffer circuit. However buying enough transistors so I can match them seems insurmountable.
I threw my hands up and now have decided to build a buffer using a high speed JFET opamp and will splice it in. That's really quite simple now that High input Z, high speed, high V op-amps are available.
I'll let you know the results in a week or two.
There is one sentence dedicated to the triangle waveform generator buffer. Sure enough my unit flunks the procedure. The procedure tells your to look at the transistors associated with the previous stage. The signal coming out of the previous stage is pristine. Like I say, it's black and white. The buffer takes a beautiful looking triangle wave and turns it into sh..t
20 years ago I got a 20 year old Heath oscilloscope kit in a yard sale. It built fine except I could not trim-out the DC offset of the input stage. Like yours, over-trust in JFET design. (Couldn't be a builder error.....) And yes, I selected a spiffy FET-input chip buffer instead of fooling with 1979 all over again.
You won't get 50 MHz or a sync-able sweep from a phone (unless its broken).
The buffer is what drives the output?
I would suspect an output transistor is bad. The scalloping is because the drive into the base is not enough to pull the output all the way on its own. Those won't be easy either. I fried some on a similar Krohn-Hite generator and discovered finding replacements was an undertaking. 50 MHz at full swing is not simple.
The buffer is what drives the output?
I would suspect an output transistor is bad. The scalloping is because the drive into the base is not enough to pull the output all the way on its own. Those won't be easy either. I fried some on a similar Krohn-Hite generator and discovered finding replacements was an undertaking. 50 MHz at full swing is not simple.
NareshBrd, this is a diy forum, which means some people like to go to an extraordinary level of effort to fix their own gear, and to seek help from others as that can often provide a better insight in to the issue at hand. There is nothing wrong with highlighting other paths to take, although 3 posts with the same redirection seems excessive to me unless the OP agrees with you and wants to pursue a different direction in this thread.
Sorry but you should know that that´s totally wrong and misleading at least for a few who don´t know better.
The distortion figures of the Wavetek 166 is nothing to call home about but a cellphone is less than a crappy toy in comparison (just like a standard PC soundcard).
I´d definitely try and repair the Wavetek 166.
My favorite generator is the 185. The semis never go bad unless you short the thing out and burn the outputs. What does go bad are the electrolytics- simple enough to replace, the solder joints where they get stressed by the switches and pots- simple enough to resolder, and the crappy IC sockets- pita but have to be replaced. Those things have kept mine working great for a lot of years.
Agreed, the 185 and 186 are nice generators. But a pain to work on (as is the 166). My vote goes to the HP 3312A.
To the OP; I understand how you feel, my batting average repairing 166's is pretty bad. I have five of them that I've put way too many hours into. A frequent issue with the 166 is the molex connectors on the power suppply module and pcbs. The solder joints of the pins to the pcb open up.
9-20-21
jbau eluded to the real problem. One of the SIP connectors was making intermittent contact. J16 passes the square wave from one board to the other. I would lose everything intermittently. When it did come back the triangle wave output buffer had a distorted output. I bought 10 FETS and matched a pair for IDss - no change. So I figured it was getting overloaded. Sure enough if I disconnected the Sine wave shaper the triangle waveform cleaned up. There are so many paths that I decided to disconnect reconnect resistors to break the path. Since this part of the circuit is after the generator servo loop you can do that without loosing the waveform. Eventually I narrowed it down to an out of adjustment trim-pot in the preamp after the sine wave shaper. Now I may have tweaked it inadvertently in my desperation. Anyway, that fixed the distorted triangle wave and voila. After running the recalibration procedure all is good!
jbau eluded to the real problem. One of the SIP connectors was making intermittent contact. J16 passes the square wave from one board to the other. I would lose everything intermittently. When it did come back the triangle wave output buffer had a distorted output. I bought 10 FETS and matched a pair for IDss - no change. So I figured it was getting overloaded. Sure enough if I disconnected the Sine wave shaper the triangle waveform cleaned up. There are so many paths that I decided to disconnect reconnect resistors to break the path. Since this part of the circuit is after the generator servo loop you can do that without loosing the waveform. Eventually I narrowed it down to an out of adjustment trim-pot in the preamp after the sine wave shaper. Now I may have tweaked it inadvertently in my desperation. Anyway, that fixed the distorted triangle wave and voila. After running the recalibration procedure all is good!
I've found that a soundcard and spectrum analyser software (I use REW) is a very easy modern method to trim sine-shaper circuits, as individual harmonic levels are visible and a lot easier to appreciate than assessing HD numbers, or worse still just a THD number.
The Wavetek 154 has a spec THD <0.5%, and I could tweak that down to 0.12%. The Wavetek 111 has a complex interplay of settings that includes offset and fundamental amplitude, and it needs an extender board to get to the myriad number of pots, and pretty much all the standard carbon composite resistors had drifted a lot.
The shaper I can't get to within spec sadly has been a HP3325A.
The Wavetek 154 has a spec THD <0.5%, and I could tweak that down to 0.12%. The Wavetek 111 has a complex interplay of settings that includes offset and fundamental amplitude, and it needs an extender board to get to the myriad number of pots, and pretty much all the standard carbon composite resistors had drifted a lot.
The shaper I can't get to within spec sadly has been a HP3325A.
